HJ
Hugo Jackson
Wed, Oct 30, 2019 4:34 AM
Begin forwarded message:
From: "Alex Gibson" alex@alexgibson.net
Subject: Re: [OpenSCAD] Engineering Fits and Tolerance
Date: October 29, 2019 at 6:45:19 PM PDT
To: "'OpenSCAD general discussion'" discuss@lists.openscad.org
Reply-To: OpenSCAD general discussion discuss@lists.openscad.org
Tolerances are to me a completely different concept than adjustments for specific CAM applications. They are used to communicate to somebody else what is acceptable when making the item you have described perfectly in CAD. So they must be a range.
Agreed. And that’s what the ISO and ANSII specifications are… they specify a range of clearance for a part.
Whereas if I know my kerf or spread factor from precise measurement, and apply this as an offset to my perfect model, I’m expecting the resulting rendered model to explicitly be a distorted rendering of my part, and that if I slice and print this using one very specific configuration, it will print/cut something closer to the perfect shape than if we’d used the ‘nominal’ part.
Especially in 3D printing, you get different tolerances in different axes- if I took a part I’d optimised for spread in x and Y, and rotated it about X, I could end up with an awfully distorted part.
Printer tuning is a subject unto itself, but I’ve found that if I spend enough time and effort I can tune my printers to provide consistent and repeatable dimensionality for the objects it prints regardless of orientation. This is not an easy task, and typically requires a unique setup for just about any parameter that can be applied to 3d printing, filament type, temperature, z layer height, hell…. Even relative humidity. For that reason I tend to buy a lot of rolls of the same brand filament and color and stick with it until a project is complete. If the final print is going to be in another color or filament brand or type, then I’ll spend the time tuning it so that combination of elements yields a print within the base tolerance of the machine.
I have some designs which have complex arrangements of laser cut parts, and the variations in thickness of the Perspex could make or break the fit. So I have a test piece that is designed to be cut and measured, to feed into OpenSCAD the top level measurements of kerf, material thickness etc. This is then picked up as a factor by all relevant parts of the design, which shuffles itself to fit.
I would call this (from ignorance of the proper term) ‘tuning’ – and it’s set apart from tolerance – perhaps the flip side.
Finally there’s also things like spacings – allowance for material expansion, air gap between moving parts etc. To me that’s handled separately from tolerance and tuning, but often all 3 might be present in a single radius…!
I think there’s always some tension between where to adjust for a model to print as close to hypothetical perfection as possible, “do I do this in the cad” or “do I tune the printer so that it prints what the cad gives it”. A PLA filament is far easier to work with as it’s relatively dimensionally stable, whereas ABS is not, but as a general rule I see it as the machine’s responsibility to print to the dimensions its been given, rather than tweaking the design to accommodate the manufacturing process… which we both see as separate from tolerance and tuning.
Regardless, a perfectly printed shaft with a 30 mm diameter will not fit in a perfectly printed 30mm hole without a lot of effort, and that’s what engineering fit is all about… sometimes we want a tight fit, sometimes we want a loose fit, it depends on the application. My point is that if we know that at the time we are in the design phase, it would be worthwhile if that were integrated into the files we produce. I may not care WHAT type of filament a part is printed in, but I do care that there’s a .5 mm clearance +/- .05 between the printed parts.
> Begin forwarded message:
>
> From: "Alex Gibson" <alex@alexgibson.net>
> Subject: Re: [OpenSCAD] Engineering Fits and Tolerance
> Date: October 29, 2019 at 6:45:19 PM PDT
> To: "'OpenSCAD general discussion'" <discuss@lists.openscad.org>
> Reply-To: OpenSCAD general discussion <discuss@lists.openscad.org>
>
>
> Tolerances are to me a completely different concept than adjustments for specific CAM applications. They are used to communicate to somebody else what is acceptable when making the item you have described perfectly in CAD. So they must be a range.
Agreed. And that’s what the ISO and ANSII specifications are… they specify a range of clearance for a part.
>
> Whereas if I know my kerf or spread factor from precise measurement, and apply this as an offset to my perfect model, I’m expecting the resulting rendered model to explicitly be a distorted rendering of my part, and that if I slice and print this using one very specific configuration, it will print/cut something closer to the perfect shape than if we’d used the ‘nominal’ part.
> Especially in 3D printing, you get different tolerances in different axes- if I took a part I’d optimised for spread in x and Y, and rotated it about X, I could end up with an awfully distorted part.
>
Printer tuning is a subject unto itself, but I’ve found that if I spend enough time and effort I can tune my printers to provide consistent and repeatable dimensionality for the objects it prints regardless of orientation. This is not an easy task, and typically requires a unique setup for just about any parameter that can be applied to 3d printing, filament type, temperature, z layer height, hell…. Even relative humidity. For that reason I tend to buy a lot of rolls of the same brand filament and color and stick with it until a project is complete. If the final print is going to be in another color or filament brand or type, then I’ll spend the time tuning it so that combination of elements yields a print within the base tolerance of the machine.
> I have some designs which have complex arrangements of laser cut parts, and the variations in thickness of the Perspex could make or break the fit. So I have a test piece that is designed to be cut and measured, to feed into OpenSCAD the top level measurements of kerf, material thickness etc. This is then picked up as a factor by all relevant parts of the design, which shuffles itself to fit.
>
> I would call this (from ignorance of the proper term) ‘tuning’ – and it’s set apart from tolerance – perhaps the flip side.
>
> Finally there’s also things like spacings – allowance for material expansion, air gap between moving parts etc. To me that’s handled separately from tolerance and tuning, but often all 3 might be present in a single radius…!
I think there’s always some tension between where to adjust for a model to print as close to hypothetical perfection as possible, “do I do this in the cad” or “do I tune the printer so that it prints what the cad gives it”. A PLA filament is far easier to work with as it’s relatively dimensionally stable, whereas ABS is not, but as a general rule I see it as the machine’s responsibility to print to the dimensions its been given, rather than tweaking the design to accommodate the manufacturing process… which we both see as separate from tolerance and tuning.
Regardless, a perfectly printed shaft with a 30 mm diameter will not fit in a perfectly printed 30mm hole without a lot of effort, and that’s what engineering fit is all about… sometimes we want a tight fit, sometimes we want a loose fit, it depends on the application. My point is that if we know that at the time we are in the design phase, it would be worthwhile if that were integrated into the files we produce. I may not care WHAT type of filament a part is printed in, but I do care that there’s a .5 mm clearance +/- .05 between the printed parts.
HJ
Hugo Jackson
Wed, Oct 30, 2019 4:57 AM
On Oct 29, 2019, at 8:40 PM, shadowwynd shadowwynd@gmail.com wrote:
If you are printing a bulbasaur, slop in the printer doesn't make much
difference.
I know what you mean, and let’s face it, the world can always use another bulbassaur if it’s cute! :)
If you are building parts that have to work with other parts - there is a
dizzying array of variables. Filament type / brand / color, humidity, flow
rate, print/bed temperature, layer height, Z-Offset, edge curl/elephant
foot, slicing algorithm, and even the infill percentage and support
structure can subtly alter the print. There are days when I marvel that any
of this FDM stuff works at all.
Indeed… but the machines ARE getting better… more reliable, more repeatability and as I mentioned
With the advent of affordable DLP machines, we’re starting to move to some impressive precision.
But as mentioned in this thread I think there’s a clear division of responsibility of the machine to print
objects to the specifications it is given. All the factors you mention are relevant to getting a machine to
print a part, but the goal is ultimately to get as close to the design specifications as possible, is it not?
If I specify I want a part that’s 30 mm wide +/- .05mm then that IS what I want… if my machine isn’t capable of
accomplishing that then I need to either find a machine that can produce those kind of tolerances or rethink my
design.
I can easily get 1mm+ difference between prints if I start changing
…
easily tweak a hole diameter by 0.2mm and it can apply to every hole in my
model at the same time.
diam = 10; // Ideal Diameter
thickness = 1; //Height
// Fudge Factors - Printing on MakerGear M2, 0.2mm layer height, brown
UltiMachine PLA
diam_e = 0.1;
thickness_e = 0.04;
/* // Fudge Factors - Printing on Makerbot, 0.3mm layer height, Hatchbox
white PLA
diam_e = 0.0;
thickness_e = 0.2;
*/
//Create Model
cylinder (d=diam+diam_e, h=thickness+thickness_e);
Personal experience shows me that I can get dimensioning of +/- .03 on a MakerGear M2, Prusa i3 Mk3 and a Monoprice mini-select and an XYZ DaVinci 1.0 Pro, for my
larger formbot I can get around +/- .07 tolerance. But that involves a lot of time intensive measurement and tuning, but as I’ve identified, I’m not
talking about Engineering Fits to address untuned printers, I’m just talking about incorporating tolerance dimensioning at a low level in OpenSCAD objects.
I confess that when I’m doing development I actually use a second dimensioning assist that is all about compensating for an untuned printer, I call it $slop. But when a project is finished $slop gets set to 0 (or [0,0,0] actually… one for each vertex) and I work with the printer to get it to printer objects of the dimensions I’ve specified rather than
having created a model that will only print accurately on the untuned printer I have sitting in front of me.
As I say, engineering fit is NOT about adjusting an untuned printer, it’s just about the clearances we want our interconnecting parts to have.
> On Oct 29, 2019, at 8:40 PM, shadowwynd <shadowwynd@gmail.com> wrote:
>
> If you are printing a bulbasaur, slop in the printer doesn't make much
> difference.
I know what you mean, and let’s face it, the world can always use another bulbassaur if it’s cute! :)
>
> If you are building parts that have to work with other parts - there is a
> dizzying array of variables. Filament type / brand / color, humidity, flow
> rate, print/bed temperature, layer height, Z-Offset, edge curl/elephant
> foot, slicing algorithm, and even the infill percentage and support
> structure can subtly alter the print. There are days when I marvel that any
> of this FDM stuff works *at all*.
Indeed… but the machines ARE getting better… more reliable, more repeatability and as I mentioned
With the advent of affordable DLP machines, we’re starting to move to some impressive precision.
But as mentioned in this thread I think there’s a clear division of responsibility of the machine to print
objects to the specifications it is given. All the factors you mention are relevant to getting a machine to
print a part, but the goal is ultimately to get as close to the design specifications as possible, is it not?
If I specify I want a part that’s 30 mm wide +/- .05mm then that IS what I want… if my machine isn’t capable of
accomplishing that then I need to either find a machine that can produce those kind of tolerances or rethink my
design.
>
> I can easily get 1mm+ difference between prints if I start changing
> …
> easily tweak a hole diameter by 0.2mm and it can apply to every hole in my
> model at the same time.
> diam = 10; // Ideal Diameter
> thickness = 1; //Height
>
> // Fudge Factors - Printing on MakerGear M2, 0.2mm layer height, brown
> UltiMachine PLA
> diam_e = 0.1;
> thickness_e = 0.04;
>
> /* // Fudge Factors - Printing on Makerbot, 0.3mm layer height, Hatchbox
> white PLA
> diam_e = 0.0;
> thickness_e = 0.2;
> */
>
> //Create Model
> cylinder (d=diam+diam_e, h=thickness+thickness_e);
>
Personal experience shows me that I can get dimensioning of +/- .03 on a MakerGear M2, Prusa i3 Mk3 and a Monoprice mini-select and an XYZ DaVinci 1.0 Pro, for my
larger formbot I can get around +/- .07 tolerance. But that involves a lot of time intensive measurement and tuning, but as I’ve identified, I’m not
talking about Engineering Fits to address untuned printers, I’m just talking about incorporating tolerance dimensioning at a low level in OpenSCAD objects.
I confess that when I’m doing development I actually use a second dimensioning assist that is all about compensating for an untuned printer, I call it $slop. But when a project is finished $slop gets set to 0 (or [0,0,0] actually… one for each vertex) and I work with the printer to get it to printer objects of the dimensions I’ve specified rather than
having created a model that will only print accurately on the untuned printer I have sitting in front of me.
As I say, engineering fit is NOT about adjusting an untuned printer, it’s just about the clearances we want our interconnecting parts to have.
NH
nop head
Wed, Oct 30, 2019 9:22 AM
My experience is totally different. The only setting I change is I measure
the filament diameter when I start a new spool. I always model in
actually dimensions. I use polyholes for round holes. If I want an
interference fit I make the dimensions the same and they always press in,
with varying degrees of force.. If I want a loose fit I leave 0.2mm gap.
Since most of my holes are clearance holes using the standards for screws
they always work because the standard is quite generous. For example 3.4mm
for an M3 clearance hole.
If I want a super accurate hole, for example a pulley bore that is supposed
to be H7 I print it slightly undersized and ream it with an H7 reamer. That
actually makes the finished hole too small because of spring back in the
plastic. But because the plastic has some spring it make a very nice snug
fit on a motor shaft. It is is very had to even measure holes in plastic
because of this.
On Wed, 30 Oct 2019 at 04:57, Hugo Jackson hugo@apres.net wrote:
On Oct 29, 2019, at 8:40 PM, shadowwynd shadowwynd@gmail.com wrote:
If you are printing a bulbasaur, slop in the printer doesn't make much
difference.
I know what you mean, and let’s face it, the world can always use another
bulbassaur if it’s cute! :)
If you are building parts that have to work with other parts - there is a
dizzying array of variables. Filament type / brand / color, humidity,
rate, print/bed temperature, layer height, Z-Offset, edge curl/elephant
foot, slicing algorithm, and even the infill percentage and support
structure can subtly alter the print. There are days when I marvel that
of this FDM stuff works at all.
Indeed… but the machines ARE getting better… more reliable, more
repeatability and as I mentioned
With the advent of affordable DLP machines, we’re starting to move to some
impressive precision.
But as mentioned in this thread I think there’s a clear division of
responsibility of the machine to print
objects to the specifications it is given. All the factors you mention are
relevant to getting a machine to
print a part, but the goal is ultimately to get as close to the design
specifications as possible, is it not?
If I specify I want a part that’s 30 mm wide +/- .05mm then that IS what I
want… if my machine isn’t capable of
accomplishing that then I need to either find a machine that can produce
those kind of tolerances or rethink my
design.
I can easily get 1mm+ difference between prints if I start changing
…
easily tweak a hole diameter by 0.2mm and it can apply to every hole in
diam = 10; // Ideal Diameter
thickness = 1; //Height
// Fudge Factors - Printing on MakerGear M2, 0.2mm layer height, brown
UltiMachine PLA
diam_e = 0.1;
thickness_e = 0.04;
/* // Fudge Factors - Printing on Makerbot, 0.3mm layer height, Hatchbox
white PLA
diam_e = 0.0;
thickness_e = 0.2;
*/
//Create Model
cylinder (d=diam+diam_e, h=thickness+thickness_e);
Personal experience shows me that I can get dimensioning of +/- .03 on a
MakerGear M2, Prusa i3 Mk3 and a Monoprice mini-select and an XYZ DaVinci
1.0 Pro, for my
larger formbot I can get around +/- .07 tolerance. But that involves a lot
of time intensive measurement and tuning, but as I’ve identified, I’m not
talking about Engineering Fits to address untuned printers, I’m just
talking about incorporating tolerance dimensioning at a low level in
OpenSCAD objects.
I confess that when I’m doing development I actually use a second
dimensioning assist that is all about compensating for an untuned printer,
I call it $slop. But when a project is finished $slop gets set to 0 (or
[0,0,0] actually… one for each vertex) and I work with the printer to get
it to printer objects of the dimensions I’ve specified rather than
having created a model that will only print accurately on the untuned
printer I have sitting in front of me.
As I say, engineering fit is NOT about adjusting an untuned printer, it’s
just about the clearances we want our interconnecting parts to have.
OpenSCAD mailing list
Discuss@lists.openscad.org
http://lists.openscad.org/mailman/listinfo/discuss_lists.openscad.org
My experience is totally different. The only setting I change is I measure
the filament diameter when I start a new spool. I always model in
actually dimensions. I use polyholes for round holes. If I want an
interference fit I make the dimensions the same and they always press in,
with varying degrees of force.. If I want a loose fit I leave 0.2mm gap.
Since most of my holes are clearance holes using the standards for screws
they always work because the standard is quite generous. For example 3.4mm
for an M3 clearance hole.
If I want a super accurate hole, for example a pulley bore that is supposed
to be H7 I print it slightly undersized and ream it with an H7 reamer. That
actually makes the finished hole too small because of spring back in the
plastic. But because the plastic has some spring it make a very nice snug
fit on a motor shaft. It is is very had to even measure holes in plastic
because of this.
On Wed, 30 Oct 2019 at 04:57, Hugo Jackson <hugo@apres.net> wrote:
>
>
> > On Oct 29, 2019, at 8:40 PM, shadowwynd <shadowwynd@gmail.com> wrote:
> >
> > If you are printing a bulbasaur, slop in the printer doesn't make much
> > difference.
>
> I know what you mean, and let’s face it, the world can always use another
> bulbassaur if it’s cute! :)
>
> >
> > If you are building parts that have to work with other parts - there is a
> > dizzying array of variables. Filament type / brand / color, humidity,
> flow
> > rate, print/bed temperature, layer height, Z-Offset, edge curl/elephant
> > foot, slicing algorithm, and even the infill percentage and support
> > structure can subtly alter the print. There are days when I marvel that
> any
> > of this FDM stuff works *at all*.
>
> Indeed… but the machines ARE getting better… more reliable, more
> repeatability and as I mentioned
> With the advent of affordable DLP machines, we’re starting to move to some
> impressive precision.
> But as mentioned in this thread I think there’s a clear division of
> responsibility of the machine to print
> objects to the specifications it is given. All the factors you mention are
> relevant to getting a machine to
> print a part, but the goal is ultimately to get as close to the design
> specifications as possible, is it not?
>
> If I specify I want a part that’s 30 mm wide +/- .05mm then that IS what I
> want… if my machine isn’t capable of
> accomplishing that then I need to either find a machine that can produce
> those kind of tolerances or rethink my
> design.
>
> >
> > I can easily get 1mm+ difference between prints if I start changing
> > …
> > easily tweak a hole diameter by 0.2mm and it can apply to every hole in
> my
> > model at the same time.
>
> > diam = 10; // Ideal Diameter
> > thickness = 1; //Height
> >
> > // Fudge Factors - Printing on MakerGear M2, 0.2mm layer height, brown
> > UltiMachine PLA
> > diam_e = 0.1;
> > thickness_e = 0.04;
> >
> > /* // Fudge Factors - Printing on Makerbot, 0.3mm layer height, Hatchbox
> > white PLA
> > diam_e = 0.0;
> > thickness_e = 0.2;
> > */
> >
> > //Create Model
> > cylinder (d=diam+diam_e, h=thickness+thickness_e);
> >
>
> Personal experience shows me that I can get dimensioning of +/- .03 on a
> MakerGear M2, Prusa i3 Mk3 and a Monoprice mini-select and an XYZ DaVinci
> 1.0 Pro, for my
> larger formbot I can get around +/- .07 tolerance. But that involves a lot
> of time intensive measurement and tuning, but as I’ve identified, I’m not
> talking about Engineering Fits to address untuned printers, I’m just
> talking about incorporating tolerance dimensioning at a low level in
> OpenSCAD objects.
>
> I confess that when I’m doing development I actually use a second
> dimensioning assist that is all about compensating for an untuned printer,
> I call it $slop. But when a project is finished $slop gets set to 0 (or
> [0,0,0] actually… one for each vertex) and I work with the printer to get
> it to printer objects of the dimensions I’ve specified rather than
> having created a model that will only print accurately on the untuned
> printer I have sitting in front of me.
>
> As I say, engineering fit is NOT about adjusting an untuned printer, it’s
> just about the clearances we want our interconnecting parts to have.
> _______________________________________________
> OpenSCAD mailing list
> Discuss@lists.openscad.org
> http://lists.openscad.org/mailman/listinfo/discuss_lists.openscad.org
>
JB
Jordan Brown
Wed, Oct 30, 2019 3:32 PM
On 10/29/2019 3:00 PM, Hugo Jackson wrote:
cylinder(d = 5, h = 2, $fit = “g6”);
So what exactly does this do to the cylinder?
On 10/29/2019 3:00 PM, Hugo Jackson wrote:
> cylinder(d = 5, h = 2, $fit = “g6”);
So what exactly does this do to the cylinder?
NH
nop head
Wed, Oct 30, 2019 9:37 PM
Yes this is what I don't get. Does it aim for the middle of the tolerance
band?
For plastic I don't think these tolerances make sense because of the
springiness.
Even with metal I don't think anybody makes these fits directly with CNC
machinery, even professionally. I think they would use a reamer, perhaps on
a turret tool changer, but not directly with a boring bar under control of
an axis. And I doubt any 3D printers are this accurate.
And what size does an H7 reamer make? I suspect it would aim for the high
side of the tolerance so it could wear down and still have some life.
I don't see the point of adding it to OpenSCAD because it is more of a
specification passed on to the machinist and checked by a QA department
than it is something that goes into the model. Please correct me if I am
wrong.
On Wed, 30 Oct 2019 at 15:33, Jordan Brown openscad@jordan.maileater.net
wrote:
Yes this is what I don't get. Does it aim for the middle of the tolerance
band?
For plastic I don't think these tolerances make sense because of the
springiness.
Even with metal I don't think anybody makes these fits directly with CNC
machinery, even professionally. I think they would use a reamer, perhaps on
a turret tool changer, but not directly with a boring bar under control of
an axis. And I doubt any 3D printers are this accurate.
And what size does an H7 reamer make? I suspect it would aim for the high
side of the tolerance so it could wear down and still have some life.
I don't see the point of adding it to OpenSCAD because it is more of a
specification passed on to the machinist and checked by a QA department
than it is something that goes into the model. Please correct me if I am
wrong.
On Wed, 30 Oct 2019 at 15:33, Jordan Brown <openscad@jordan.maileater.net>
wrote:
> On 10/29/2019 3:00 PM, Hugo Jackson wrote:
>
> cylinder(d = 5, h = 2, $fit = “g6”);
>
>
> So what exactly does this do to the cylinder?
>
> _______________________________________________
> OpenSCAD mailing list
> Discuss@lists.openscad.org
> http://lists.openscad.org/mailman/listinfo/discuss_lists.openscad.org
>
AG
Alex Gibson
Thu, Oct 31, 2019 11:28 AM
Going back to your original question Hugh, and your example:
cylinder(d = 5, h = 2, $fit = “g6”);
The way I've seen a lot of machine parts (usually 3D printer) programmed in OpenSCAD is this:
cylinder(d = g6, h = 2);
...and above this at the top of the file...
fit_tolerance = 0.5;
machine_tolerance = 0.2;
g6 = 5+fit_tolerance+machine_tolerance;
Rather than being 'piecemeal' I think building up layers of tolerance like this can be very helpful and reduce confusion and repetitive typing within the body of your design code. Every time you want that size hole in your project, you just use d= g6 by name. You can tune the tolerances after the initial design without re-coding.
The idea of a global $fit variable seems nice, but you would have to have it associated with a big table which defines what g6 and many other tolerances are, which you'd need to remember as you are designing the part. Also it could not take into account multiple fudge factors, and to me that's the real beauty of OpenSCAD for this sort of thing.
Have you tried a similar method, defining named dimensions?
One think I've started to do in my recent bigger projects is to break out dimensions and specific geometry modules into their own separate files:
0_dimensions.scad <named dimensions - for example m3_bolt_hole = 3.2; < this is where I do all tolerances etc.
1_geometry.scad <for example Nema 17 mount pattern holes, as a 2D pattern
2_component <say a 3D printed mount for the motor
3_subassembly <say the mount with motor, screws, pulley etc
4_majorassembly <say the whole axis
5_render <the whole project for rendering.
This has really helped me to improve version control and ease of navigation around complex projects - and made it easier to recycle code and incorporate scanned or downloaded parts.
Cheers
Alex Gibson
admg consulting
edumaker limited
• Project management
• Operations & Process improvement
• 3D Printing
-----Original Message-----
From: Discuss [mailto:discuss-bounces@lists.openscad.org] On Behalf Of Hugo Jackson
Sent: 29 October 2019 22:00
To: OpenSCAD general discussion
Subject: [OpenSCAD] Engineering Fits and Tolerance
Has any thought been given to incorporating engineering fits and tolerances into OpenSCAD? As I understand it, OpenSCAD was originally conceived for the creation of STL files for a 3D printer and I’ve been thinking that the base functionality might be improved by a little more CAM in the CAD.
For some time I’ve been using wrappers around most of the OpenSCAD modules in order to introduce engineering fits into the parts I create as 3d printers on the whole offer increasing precision and repeatability.
Using a special variable $fit I can arbitrarily call up a module and it will adjust the the final size of the geometry according to the engineering fit I specify. e.g.
cylinder(d = 5, h = 2, $fit = “g6”);
I think anyone who has created interconnecting parts is familiar with the requirement to adjust for tolerance, but the core language as it stands requires this to be accomplished on a piecemeal basis, but to my way of thinking fit and tolerance are integral to the original purpose of OpenSCAD.
I think this is particularly relevant as more and more users are acquiring machines that use different processes and that I might well wish to print a part on an FDM printer one day and a DLP the next, which I think would naturally call for a different fit specification.
I also created some constants: kLeft, kRight, kFront, kBack, kTop & kBottom and use 6 element arrays to selectively apply tolerance, and use a special variable $faces to pass on that information as required:
cube([7,3,8], $fit = “H11”, $faces = kLeft + kRight);
And of course if I’m creating a project with lots of references to fit then I simply create an identifier for the fit, e.g.
shaftFit = “h7”;
So that if I move to a different type of machine where more or less tolerance is indicated, I only need to change the definition of shaftFit.
I did some poking around in the mailing list archives and couldn’t see any reference to a discussion on this, but I’m sure it’s occurred to others before me, I just thought I’d ask where the community stands on incorporating this kind of functionality into the core language.
OpenSCAD mailing list
Discuss@lists.openscad.org
http://lists.openscad.org/mailman/listinfo/discuss_lists.openscad.org
Going back to your original question Hugh, and your example:
cylinder(d = 5, h = 2, $fit = “g6”);
The way I've seen a lot of machine parts (usually 3D printer) programmed in OpenSCAD is this:
cylinder(d = g6, h = 2);
...and above this at the top of the file...
fit_tolerance = 0.5;
machine_tolerance = 0.2;
g6 = 5+fit_tolerance+machine_tolerance;
Rather than being 'piecemeal' I think building up layers of tolerance like this can be very helpful and reduce confusion and repetitive typing within the body of your design code. Every time you want that size hole in your project, you just use d= g6 by name. You can tune the tolerances after the initial design without re-coding.
The idea of a global $fit variable seems nice, but you would have to have it associated with a big table which defines what g6 and many other tolerances are, which you'd need to remember as you are designing the part. Also it could not take into account multiple fudge factors, and to me that's the real beauty of OpenSCAD for this sort of thing.
Have you tried a similar method, defining named dimensions?
One think I've started to do in my recent bigger projects is to break out dimensions and specific geometry modules into their own separate files:
0_dimensions.scad <named dimensions - for example m3_bolt_hole = 3.2; < this is where I do all tolerances etc.
1_geometry.scad <for example Nema 17 mount pattern holes, as a 2D pattern
2_component <say a 3D printed mount for the motor
3_subassembly <say the mount with motor, screws, pulley etc
4_majorassembly <say the whole axis
5_render <the whole project for rendering.
This has really helped me to improve version control and ease of navigation around complex projects - and made it easier to recycle code and incorporate scanned or downloaded parts.
Cheers
Alex Gibson
admg consulting
edumaker limited
• Project management
• Operations & Process improvement
• 3D Printing
-----Original Message-----
From: Discuss [mailto:discuss-bounces@lists.openscad.org] On Behalf Of Hugo Jackson
Sent: 29 October 2019 22:00
To: OpenSCAD general discussion
Subject: [OpenSCAD] Engineering Fits and Tolerance
Has any thought been given to incorporating engineering fits and tolerances into OpenSCAD? As I understand it, OpenSCAD was originally conceived for the creation of STL files for a 3D printer and I’ve been thinking that the base functionality might be improved by a little more CAM in the CAD.
For some time I’ve been using wrappers around most of the OpenSCAD modules in order to introduce engineering fits into the parts I create as 3d printers on the whole offer increasing precision and repeatability.
Using a special variable $fit I can arbitrarily call up a module and it will adjust the the final size of the geometry according to the engineering fit I specify. e.g.
cylinder(d = 5, h = 2, $fit = “g6”);
I think anyone who has created interconnecting parts is familiar with the requirement to adjust for tolerance, but the core language as it stands requires this to be accomplished on a piecemeal basis, but to my way of thinking fit and tolerance are integral to the original purpose of OpenSCAD.
I think this is particularly relevant as more and more users are acquiring machines that use different processes and that I might well wish to print a part on an FDM printer one day and a DLP the next, which I think would naturally call for a different fit specification.
I also created some constants: kLeft, kRight, kFront, kBack, kTop & kBottom and use 6 element arrays to selectively apply tolerance, and use a special variable $faces to pass on that information as required:
cube([7,3,8], $fit = “H11”, $faces = kLeft + kRight);
And of course if I’m creating a project with lots of references to fit then I simply create an identifier for the fit, e.g.
shaftFit = “h7”;
So that if I move to a different type of machine where more or less tolerance is indicated, I only need to change the definition of shaftFit.
I did some poking around in the mailing list archives and couldn’t see any reference to a discussion on this, but I’m sure it’s occurred to others before me, I just thought I’d ask where the community stands on incorporating this kind of functionality into the core language.
_______________________________________________
OpenSCAD mailing list
Discuss@lists.openscad.org
http://lists.openscad.org/mailman/listinfo/discuss_lists.openscad.org
NH
nop head
Thu, Oct 31, 2019 2:44 PM
There is no final size for h7, etc. It is a tolerance range and depends on
the diameter, so it would need to be a function. But as I said before I
can't see how you can apply it to the model to be made. STL files do not
convey tolerances. The best you could do is aim for the mid value but I
don't know any machines that can make parts that accurate from an STL file.
On Thu, 31 Oct 2019 at 11:32, Alex Gibson alex@alexgibson.net wrote:
Going back to your original question Hugh, and your example:
cylinder(d = 5, h = 2, $fit = “g6”);
The way I've seen a lot of machine parts (usually 3D printer) programmed
in OpenSCAD is this:
cylinder(d = g6, h = 2);
...and above this at the top of the file...
fit_tolerance = 0.5;
machine_tolerance = 0.2;
g6 = 5+fit_tolerance+machine_tolerance;
Rather than being 'piecemeal' I think building up layers of tolerance like
this can be very helpful and reduce confusion and repetitive typing within
the body of your design code. Every time you want that size hole in your
project, you just use d= g6 by name. You can tune the tolerances after the
initial design without re-coding.
The idea of a global $fit variable seems nice, but you would have to have
it associated with a big table which defines what g6 and many other
tolerances are, which you'd need to remember as you are designing the
part. Also it could not take into account multiple fudge factors, and to
me that's the real beauty of OpenSCAD for this sort of thing.
Have you tried a similar method, defining named dimensions?
One think I've started to do in my recent bigger projects is to break out
dimensions and specific geometry modules into their own separate files:
0_dimensions.scad <named dimensions - for example
m3_bolt_hole = 3.2; < this is where I do all tolerances
etc.
1_geometry.scad <for example Nema 17 mount pattern holes, as a 2D
pattern
2_component <say a 3D printed mount for the motor
3_subassembly <say the mount with motor, screws, pulley
etc
4_majorassembly <say the whole axis
5_render <the whole project for rendering.
This has really helped me to improve version control and ease of
navigation around complex projects - and made it easier to recycle code and
incorporate scanned or downloaded parts.
Cheers
Alex Gibson
admg consulting
edumaker limited
• Project management
• Operations & Process improvement
• 3D Printing
-----Original Message-----
From: Discuss [mailto:discuss-bounces@lists.openscad.org] On Behalf Of
Hugo Jackson
Sent: 29 October 2019 22:00
To: OpenSCAD general discussion
Subject: [OpenSCAD] Engineering Fits and Tolerance
Has any thought been given to incorporating engineering fits and
tolerances into OpenSCAD? As I understand it, OpenSCAD was originally
conceived for the creation of STL files for a 3D printer and I’ve been
thinking that the base functionality might be improved by a little more CAM
in the CAD.
For some time I’ve been using wrappers around most of the OpenSCAD modules
in order to introduce engineering fits into the parts I create as 3d
printers on the whole offer increasing precision and repeatability.
Using a special variable $fit I can arbitrarily call up a module and it
will adjust the the final size of the geometry according to the engineering
fit I specify. e.g.
cylinder(d = 5, h = 2, $fit = “g6”);
I think anyone who has created interconnecting parts is familiar with the
requirement to adjust for tolerance, but the core language as it stands
requires this to be accomplished on a piecemeal basis, but to my way of
thinking fit and tolerance are integral to the original purpose of OpenSCAD.
I think this is particularly relevant as more and more users are acquiring
machines that use different processes and that I might well wish to print a
part on an FDM printer one day and a DLP the next, which I think would
naturally call for a different fit specification.
I also created some constants: kLeft, kRight, kFront, kBack, kTop &
kBottom and use 6 element arrays to selectively apply tolerance, and use a
special variable $faces to pass on that information as required:
cube([7,3,8], $fit = “H11”, $faces = kLeft + kRight);
And of course if I’m creating a project with lots of references to fit
then I simply create an identifier for the fit, e.g.
shaftFit = “h7”;
So that if I move to a different type of machine where more or less
tolerance is indicated, I only need to change the definition of shaftFit.
I did some poking around in the mailing list archives and couldn’t see any
reference to a discussion on this, but I’m sure it’s occurred to others
before me, I just thought I’d ask where the community stands on
incorporating this kind of functionality into the core language.
OpenSCAD mailing list
Discuss@lists.openscad.org
http://lists.openscad.org/mailman/listinfo/discuss_lists.openscad.org
OpenSCAD mailing list
Discuss@lists.openscad.org
http://lists.openscad.org/mailman/listinfo/discuss_lists.openscad.org
There is no final size for h7, etc. It is a tolerance range and depends on
the diameter, so it would need to be a function. But as I said before I
can't see how you can apply it to the model to be made. STL files do not
convey tolerances. The best you could do is aim for the mid value but I
don't know any machines that can make parts that accurate from an STL file.
On Thu, 31 Oct 2019 at 11:32, Alex Gibson <alex@alexgibson.net> wrote:
> Going back to your original question Hugh, and your example:
> cylinder(d = 5, h = 2, $fit = “g6”);
>
> The way I've seen a lot of machine parts (usually 3D printer) programmed
> in OpenSCAD is this:
>
> cylinder(d = g6, h = 2);
>
> ...and above this at the top of the file...
> fit_tolerance = 0.5;
> machine_tolerance = 0.2;
> g6 = 5+fit_tolerance+machine_tolerance;
>
> Rather than being 'piecemeal' I think building up layers of tolerance like
> this can be very helpful and reduce confusion and repetitive typing within
> the body of your design code. Every time you want that size hole in your
> project, you just use d= g6 by name. You can tune the tolerances after the
> initial design without re-coding.
>
> The idea of a global $fit variable seems nice, but you would have to have
> it associated with a big table which defines what g6 and many other
> tolerances are, which you'd need to remember as you are designing the
> part. Also it could not take into account multiple fudge factors, and to
> me that's the real beauty of OpenSCAD for this sort of thing.
>
> Have you tried a similar method, defining named dimensions?
>
> One think I've started to do in my recent bigger projects is to break out
> dimensions and specific geometry modules into their own separate files:
>
> 0_dimensions.scad <named dimensions - for example
> m3_bolt_hole = 3.2; < this is where I do all tolerances
> etc.
> 1_geometry.scad <for example Nema 17 mount pattern holes, as a 2D
> pattern
> 2_component <say a 3D printed mount for the motor
> 3_subassembly <say the mount with motor, screws, pulley
> etc
> 4_majorassembly <say the whole axis
> 5_render <the whole project for rendering.
>
>
> This has really helped me to improve version control and ease of
> navigation around complex projects - and made it easier to recycle code and
> incorporate scanned or downloaded parts.
>
> Cheers
>
> Alex Gibson
>
> admg consulting
>
> edumaker limited
>
> • Project management
> • Operations & Process improvement
> • 3D Printing
>
> -----Original Message-----
> From: Discuss [mailto:discuss-bounces@lists.openscad.org] On Behalf Of
> Hugo Jackson
> Sent: 29 October 2019 22:00
> To: OpenSCAD general discussion
> Subject: [OpenSCAD] Engineering Fits and Tolerance
>
> Has any thought been given to incorporating engineering fits and
> tolerances into OpenSCAD? As I understand it, OpenSCAD was originally
> conceived for the creation of STL files for a 3D printer and I’ve been
> thinking that the base functionality might be improved by a little more CAM
> in the CAD.
>
> For some time I’ve been using wrappers around most of the OpenSCAD modules
> in order to introduce engineering fits into the parts I create as 3d
> printers on the whole offer increasing precision and repeatability.
>
> Using a special variable $fit I can arbitrarily call up a module and it
> will adjust the the final size of the geometry according to the engineering
> fit I specify. e.g.
>
> cylinder(d = 5, h = 2, $fit = “g6”);
>
> I think anyone who has created interconnecting parts is familiar with the
> requirement to adjust for tolerance, but the core language as it stands
> requires this to be accomplished on a piecemeal basis, but to my way of
> thinking fit and tolerance are integral to the original purpose of OpenSCAD.
>
> I think this is particularly relevant as more and more users are acquiring
> machines that use different processes and that I might well wish to print a
> part on an FDM printer one day and a DLP the next, which I think would
> naturally call for a different fit specification.
>
> I also created some constants: kLeft, kRight, kFront, kBack, kTop &
> kBottom and use 6 element arrays to selectively apply tolerance, and use a
> special variable $faces to pass on that information as required:
>
> cube([7,3,8], $fit = “H11”, $faces = kLeft + kRight);
>
> And of course if I’m creating a project with lots of references to fit
> then I simply create an identifier for the fit, e.g.
>
> shaftFit = “h7”;
>
> So that if I move to a different type of machine where more or less
> tolerance is indicated, I only need to change the definition of shaftFit.
>
> I did some poking around in the mailing list archives and couldn’t see any
> reference to a discussion on this, but I’m sure it’s occurred to others
> before me, I just thought I’d ask where the community stands on
> incorporating this kind of functionality into the core language.
>
>
> _______________________________________________
> OpenSCAD mailing list
> Discuss@lists.openscad.org
> http://lists.openscad.org/mailman/listinfo/discuss_lists.openscad.org
>
>
> _______________________________________________
> OpenSCAD mailing list
> Discuss@lists.openscad.org
> http://lists.openscad.org/mailman/listinfo/discuss_lists.openscad.org
>
HJ
Hugo Jackson
Thu, Oct 31, 2019 6:04 PM
On Oct 31, 2019, at 4:28 AM, Alex Gibson alex@alexgibson.net wrote:
Going back to your original question Hugh, and your example:
cylinder(d = 5, h = 2, $fit = “g6”);
The way I've seen a lot of machine parts (usually 3D printer) programmed in OpenSCAD is this:
cylinder(d = g6, h = 2);
...and above this at the top of the file...
fit_tolerance = 0.5;
machine_tolerance = 0.2;
g6 = 5+fit_tolerance+machine_tolerance;
Rather than being 'piecemeal' I think building up layers of tolerance like this can be very helpful and reduce confusion and repetitive typing within the body of your design code. Every time you want that size hole in your project, you just use d= g6 by name. You can tune the tolerances after the initial design without re-coding.
The idea of a global $fit variable seems nice, but you would have to have it associated with a big table which defines what g6 and many other tolerances are, which you'd need to remember as you are designing the part. Also it could not take into account multiple fudge factors, and to me that's the real beauty of OpenSCAD for this sort of thing.
A very big table is exactly what I have,,, and it’s the table lookup and syntax parsing that would be nice to have handled faster and more efficiently by the core.
I guess it just comes down to personal style and one’s personal understanding of the OpenSCAD zeit. I think much is made of OpenSCAD’s parametric ability for resizing and substitution of dimensions and as different printing methodologies start being added, I think that the OpenSCAD core would benefit with a nod to ‘parametric’ tolerance.
In the example you sight, you identify g6 as a calculation involving the nominal dimensions, the fit tolerance and the machine tolerance… and to my way of thinking what’s going on would be clearer and more easily amended with the scheme I use… rather than:
fit_tolerance = 0.5;
machine_tolerance = 0.2;
g6 = 5+fit_tolerance+machine_tolerance;
I think:
cylinder(d = 5, h = 2, $fit = “g6”);
Is more straightforward, particularly if one declares the fit itself as a value, such as:
runFit = “g6”;
And so:
cylinder(d = 5, h = 2, $fit = runFit);
Provides the same opportunity to quickly amend all geometric constructions that use the runFit tolerance. This is particularly relevant to resizing as the ISO and ANSI standards reflect the reality that a 5mm hole requires a different tolerance than a 10mm hole to effect the same fit.
Have you tried a similar method, defining named dimensions?
One think I've started to do in my recent bigger projects is to break out dimensions and specific geometry modules into their own separate files:
0_dimensions.scad <named dimensions - for example m3_bolt_hole = 3.2; < this is where I do all tolerances etc.
1_geometry.scad <for example Nema 17 mount pattern holes, as a 2D pattern
2_component <say a 3D printed mount for the motor
3_subassembly <say the mount with motor, screws, pulley etc
4_majorassembly <say the whole axis
5_render <the whole project for rendering.
Yes, good idea. I think as our projects get more complex we all start creating a fistful of files… and I’m also hoping some day that OpenSCAD will allow for use, include and import to use non literal string values… but that’s another topic. :)
This has really helped me to improve version control and ease of navigation around complex projects - and made it easier to recycle code and incorporate scanned or downloaded parts.
Cheers
Alex Gibson
admg consulting
edumaker limited
• Project management
• Operations & Process improvement
• 3D Printing
-----Original Message-----
From: Discuss [mailto:discuss-bounces@lists.openscad.org] On Behalf Of Hugo Jackson
Sent: 29 October 2019 22:00
To: OpenSCAD general discussion
Subject: [OpenSCAD] Engineering Fits and Tolerance
Has any thought been given to incorporating engineering fits and tolerances into OpenSCAD? As I understand it, OpenSCAD was originally conceived for the creation of STL files for a 3D printer and I’ve been thinking that the base functionality might be improved by a little more CAM in the CAD.
For some time I’ve been using wrappers around most of the OpenSCAD modules in order to introduce engineering fits into the parts I create as 3d printers on the whole offer increasing precision and repeatability.
Using a special variable $fit I can arbitrarily call up a module and it will adjust the the final size of the geometry according to the engineering fit I specify. e.g.
cylinder(d = 5, h = 2, $fit = “g6”);
I think anyone who has created interconnecting parts is familiar with the requirement to adjust for tolerance, but the core language as it stands requires this to be accomplished on a piecemeal basis, but to my way of thinking fit and tolerance are integral to the original purpose of OpenSCAD.
I think this is particularly relevant as more and more users are acquiring machines that use different processes and that I might well wish to print a part on an FDM printer one day and a DLP the next, which I think would naturally call for a different fit specification.
I also created some constants: kLeft, kRight, kFront, kBack, kTop & kBottom and use 6 element arrays to selectively apply tolerance, and use a special variable $faces to pass on that information as required:
cube([7,3,8], $fit = “H11”, $faces = kLeft + kRight);
And of course if I’m creating a project with lots of references to fit then I simply create an identifier for the fit, e.g.
shaftFit = “h7”;
So that if I move to a different type of machine where more or less tolerance is indicated, I only need to change the definition of shaftFit.
I did some poking around in the mailing list archives and couldn’t see any reference to a discussion on this, but I’m sure it’s occurred to others before me, I just thought I’d ask where the community stands on incorporating this kind of functionality into the core language.
OpenSCAD mailing list
Discuss@lists.openscad.org
http://lists.openscad.org/mailman/listinfo/discuss_lists.openscad.org
OpenSCAD mailing list
Discuss@lists.openscad.org
http://lists.openscad.org/mailman/listinfo/discuss_lists.openscad.org
> On Oct 31, 2019, at 4:28 AM, Alex Gibson <alex@alexgibson.net> wrote:
>
> Going back to your original question Hugh, and your example:
> cylinder(d = 5, h = 2, $fit = “g6”);
>
> The way I've seen a lot of machine parts (usually 3D printer) programmed in OpenSCAD is this:
>
> cylinder(d = g6, h = 2);
>
> ...and above this at the top of the file...
> fit_tolerance = 0.5;
> machine_tolerance = 0.2;
> g6 = 5+fit_tolerance+machine_tolerance;
>
> Rather than being 'piecemeal' I think building up layers of tolerance like this can be very helpful and reduce confusion and repetitive typing within the body of your design code. Every time you want that size hole in your project, you just use d= g6 by name. You can tune the tolerances after the initial design without re-coding.
>
> The idea of a global $fit variable seems nice, but you would have to have it associated with a big table which defines what g6 and many other tolerances are, which you'd need to remember as you are designing the part. Also it could not take into account multiple fudge factors, and to me that's the real beauty of OpenSCAD for this sort of thing.
A very big table is exactly what I have,,, and it’s the table lookup and syntax parsing that would be nice to have handled faster and more efficiently by the core.
I guess it just comes down to personal style and one’s personal understanding of the OpenSCAD zeit. I think much is made of OpenSCAD’s parametric ability for resizing and substitution of dimensions and as different printing methodologies start being added, I think that the OpenSCAD core would benefit with a nod to ‘parametric’ tolerance.
In the example you sight, you identify g6 as a calculation involving the nominal dimensions, the fit tolerance and the machine tolerance… and to my way of thinking what’s going on would be clearer and more easily amended with the scheme I use… rather than:
>> fit_tolerance = 0.5;
>> machine_tolerance = 0.2;
>> g6 = 5+fit_tolerance+machine_tolerance;
> cylinder(d = g6, h = 2);
I think:
cylinder(d = 5, h = 2, $fit = “g6”);
Is more straightforward, particularly if one declares the fit itself as a value, such as:
runFit = “g6”;
And so:
cylinder(d = 5, h = 2, $fit = runFit);
Provides the same opportunity to quickly amend all geometric constructions that use the runFit tolerance. This is particularly relevant to resizing as the ISO and ANSI standards reflect the reality that a 5mm hole requires a different tolerance than a 10mm hole to effect the same fit.
>
> Have you tried a similar method, defining named dimensions?
>
> One think I've started to do in my recent bigger projects is to break out dimensions and specific geometry modules into their own separate files:
>
> 0_dimensions.scad <named dimensions - for example m3_bolt_hole = 3.2; < this is where I do all tolerances etc.
> 1_geometry.scad <for example Nema 17 mount pattern holes, as a 2D pattern
> 2_component <say a 3D printed mount for the motor
> 3_subassembly <say the mount with motor, screws, pulley etc
> 4_majorassembly <say the whole axis
> 5_render <the whole project for rendering.
Yes, good idea. I think as our projects get more complex we all start creating a fistful of files… and I’m also hoping some day that OpenSCAD will allow for use, include and import to use non literal string values… but that’s another topic. :)
>
>
> This has really helped me to improve version control and ease of navigation around complex projects - and made it easier to recycle code and incorporate scanned or downloaded parts.
>
> Cheers
>
> Alex Gibson
>
> admg consulting
>
> edumaker limited
>
> • Project management
> • Operations & Process improvement
> • 3D Printing
>
> -----Original Message-----
> From: Discuss [mailto:discuss-bounces@lists.openscad.org] On Behalf Of Hugo Jackson
> Sent: 29 October 2019 22:00
> To: OpenSCAD general discussion
> Subject: [OpenSCAD] Engineering Fits and Tolerance
>
> Has any thought been given to incorporating engineering fits and tolerances into OpenSCAD? As I understand it, OpenSCAD was originally conceived for the creation of STL files for a 3D printer and I’ve been thinking that the base functionality might be improved by a little more CAM in the CAD.
>
> For some time I’ve been using wrappers around most of the OpenSCAD modules in order to introduce engineering fits into the parts I create as 3d printers on the whole offer increasing precision and repeatability.
>
> Using a special variable $fit I can arbitrarily call up a module and it will adjust the the final size of the geometry according to the engineering fit I specify. e.g.
>
> cylinder(d = 5, h = 2, $fit = “g6”);
>
> I think anyone who has created interconnecting parts is familiar with the requirement to adjust for tolerance, but the core language as it stands requires this to be accomplished on a piecemeal basis, but to my way of thinking fit and tolerance are integral to the original purpose of OpenSCAD.
>
> I think this is particularly relevant as more and more users are acquiring machines that use different processes and that I might well wish to print a part on an FDM printer one day and a DLP the next, which I think would naturally call for a different fit specification.
>
> I also created some constants: kLeft, kRight, kFront, kBack, kTop & kBottom and use 6 element arrays to selectively apply tolerance, and use a special variable $faces to pass on that information as required:
>
> cube([7,3,8], $fit = “H11”, $faces = kLeft + kRight);
>
> And of course if I’m creating a project with lots of references to fit then I simply create an identifier for the fit, e.g.
>
> shaftFit = “h7”;
>
> So that if I move to a different type of machine where more or less tolerance is indicated, I only need to change the definition of shaftFit.
>
> I did some poking around in the mailing list archives and couldn’t see any reference to a discussion on this, but I’m sure it’s occurred to others before me, I just thought I’d ask where the community stands on incorporating this kind of functionality into the core language.
>
>
> _______________________________________________
> OpenSCAD mailing list
> Discuss@lists.openscad.org
> http://lists.openscad.org/mailman/listinfo/discuss_lists.openscad.org
>
>
> _______________________________________________
> OpenSCAD mailing list
> Discuss@lists.openscad.org
> http://lists.openscad.org/mailman/listinfo/discuss_lists.openscad.org
NH
nop head
Thu, Oct 31, 2019 6:19 PM
I think you completely misunderstand what g6 tolerance means. It is isn't a
clearance that you add to the nominal size and it certainly isn't 0.5mm.
A g6 5mm shaft has to be between 4.9960 and 4.9880mm. Good luck with that
on a 3D printer with 0.2mm accuracy.
On Thu, 31 Oct 2019 at 18:05, Hugo Jackson hugo@apres.net wrote:
On Oct 31, 2019, at 4:28 AM, Alex Gibson alex@alexgibson.net wrote:
Going back to your original question Hugh, and your example:
cylinder(d = 5, h = 2, $fit = “g6”);
The way I've seen a lot of machine parts (usually 3D printer) programmed
cylinder(d = g6, h = 2);
...and above this at the top of the file...
fit_tolerance = 0.5;
machine_tolerance = 0.2;
g6 = 5+fit_tolerance+machine_tolerance;
Rather than being 'piecemeal' I think building up layers of tolerance
like this can be very helpful and reduce confusion and repetitive typing
within the body of your design code. Every time you want that size hole in
your project, you just use d= g6 by name. You can tune the tolerances
after the initial design without re-coding.
The idea of a global $fit variable seems nice, but you would have to
have it associated with a big table which defines what g6 and many other
tolerances are, which you'd need to remember as you are designing the
part. Also it could not take into account multiple fudge factors, and to
me that's the real beauty of OpenSCAD for this sort of thing.
A very big table is exactly what I have,,, and it’s the table lookup and
syntax parsing that would be nice to have handled faster and more
efficiently by the core.
I guess it just comes down to personal style and one’s personal
understanding of the OpenSCAD zeit. I think much is made of OpenSCAD’s
parametric ability for resizing and substitution of dimensions and as
different printing methodologies start being added, I think that the
OpenSCAD core would benefit with a nod to ‘parametric’ tolerance.
In the example you sight, you identify g6 as a calculation involving the
nominal dimensions, the fit tolerance and the machine tolerance… and to my
way of thinking what’s going on would be clearer and more easily amended
with the scheme I use… rather than:
fit_tolerance = 0.5;
machine_tolerance = 0.2;
g6 = 5+fit_tolerance+machine_tolerance;
I think:
cylinder(d = 5, h = 2, $fit = “g6”);
Is more straightforward, particularly if one declares the fit itself as a
value, such as:
runFit = “g6”;
And so:
cylinder(d = 5, h = 2, $fit = runFit);
Provides the same opportunity to quickly amend all geometric constructions
that use the runFit tolerance. This is particularly relevant to resizing as
the ISO and ANSI standards reflect the reality that a 5mm hole requires a
different tolerance than a 10mm hole to effect the same fit.
Have you tried a similar method, defining named dimensions?
One think I've started to do in my recent bigger projects is to break
out dimensions and specific geometry modules into their own separate files:
0_dimensions.scad <named dimensions - for example
m3_bolt_hole = 3.2; < this is where I do all tolerances
etc.
1_geometry.scad <for example Nema 17 mount pattern holes,
2_component <say a 3D printed mount for the motor
3_subassembly <say the mount with motor, screws, pulley
4_majorassembly <say the whole axis
5_render <the whole project for rendering.
Yes, good idea. I think as our projects get more complex we all start
creating a fistful of files… and I’m also hoping some day that OpenSCAD
will allow for use, include and import to use non literal string values…
but that’s another topic. :)
This has really helped me to improve version control and ease of
navigation around complex projects - and made it easier to recycle code and
incorporate scanned or downloaded parts.
Cheers
Alex Gibson
admg consulting
edumaker limited
• Project management
• Operations & Process improvement
• 3D Printing
-----Original Message-----
From: Discuss [mailto:discuss-bounces@lists.openscad.org] On Behalf Of
Sent: 29 October 2019 22:00
To: OpenSCAD general discussion
Subject: [OpenSCAD] Engineering Fits and Tolerance
Has any thought been given to incorporating engineering fits and
tolerances into OpenSCAD? As I understand it, OpenSCAD was originally
conceived for the creation of STL files for a 3D printer and I’ve been
thinking that the base functionality might be improved by a little more CAM
in the CAD.
For some time I’ve been using wrappers around most of the OpenSCAD
modules in order to introduce engineering fits into the parts I create as
3d printers on the whole offer increasing precision and repeatability.
Using a special variable $fit I can arbitrarily call up a module and it
will adjust the the final size of the geometry according to the engineering
fit I specify. e.g.
cylinder(d = 5, h = 2, $fit = “g6”);
I think anyone who has created interconnecting parts is familiar with
the requirement to adjust for tolerance, but the core language as it stands
requires this to be accomplished on a piecemeal basis, but to my way of
thinking fit and tolerance are integral to the original purpose of OpenSCAD.
I think this is particularly relevant as more and more users are
acquiring machines that use different processes and that I might well wish
to print a part on an FDM printer one day and a DLP the next, which I think
would naturally call for a different fit specification.
I also created some constants: kLeft, kRight, kFront, kBack, kTop &
kBottom and use 6 element arrays to selectively apply tolerance, and use a
special variable $faces to pass on that information as required:
cube([7,3,8], $fit = “H11”, $faces = kLeft + kRight);
And of course if I’m creating a project with lots of references to fit
then I simply create an identifier for the fit, e.g.
shaftFit = “h7”;
So that if I move to a different type of machine where more or less
tolerance is indicated, I only need to change the definition of shaftFit.
I did some poking around in the mailing list archives and couldn’t see
any reference to a discussion on this, but I’m sure it’s occurred to others
before me, I just thought I’d ask where the community stands on
incorporating this kind of functionality into the core language.
I think you completely misunderstand what g6 tolerance means. It is isn't a
clearance that you add to the nominal size and it certainly isn't 0.5mm.
A g6 5mm shaft has to be between 4.9960 and 4.9880mm. Good luck with that
on a 3D printer with 0.2mm accuracy.
On Thu, 31 Oct 2019 at 18:05, Hugo Jackson <hugo@apres.net> wrote:
>
> > On Oct 31, 2019, at 4:28 AM, Alex Gibson <alex@alexgibson.net> wrote:
> >
> > Going back to your original question Hugh, and your example:
> > cylinder(d = 5, h = 2, $fit = “g6”);
> >
> > The way I've seen a lot of machine parts (usually 3D printer) programmed
> in OpenSCAD is this:
> >
> > cylinder(d = g6, h = 2);
> >
> > ...and above this at the top of the file...
> > fit_tolerance = 0.5;
> > machine_tolerance = 0.2;
> > g6 = 5+fit_tolerance+machine_tolerance;
> >
> > Rather than being 'piecemeal' I think building up layers of tolerance
> like this can be very helpful and reduce confusion and repetitive typing
> within the body of your design code. Every time you want that size hole in
> your project, you just use d= g6 by name. You can tune the tolerances
> after the initial design without re-coding.
> >
> > The idea of a global $fit variable seems nice, but you would have to
> have it associated with a big table which defines what g6 and many other
> tolerances are, which you'd need to remember as you are designing the
> part. Also it could not take into account multiple fudge factors, and to
> me that's the real beauty of OpenSCAD for this sort of thing.
>
> A very big table is exactly what I have,,, and it’s the table lookup and
> syntax parsing that would be nice to have handled faster and more
> efficiently by the core.
>
> I guess it just comes down to personal style and one’s personal
> understanding of the OpenSCAD zeit. I think much is made of OpenSCAD’s
> parametric ability for resizing and substitution of dimensions and as
> different printing methodologies start being added, I think that the
> OpenSCAD core would benefit with a nod to ‘parametric’ tolerance.
>
> In the example you sight, you identify g6 as a calculation involving the
> nominal dimensions, the fit tolerance and the machine tolerance… and to my
> way of thinking what’s going on would be clearer and more easily amended
> with the scheme I use… rather than:
>
> >> fit_tolerance = 0.5;
> >> machine_tolerance = 0.2;
> >> g6 = 5+fit_tolerance+machine_tolerance;
>
> > cylinder(d = g6, h = 2);
>
> I think:
>
> cylinder(d = 5, h = 2, $fit = “g6”);
>
> Is more straightforward, particularly if one declares the fit itself as a
> value, such as:
>
> runFit = “g6”;
>
> And so:
>
> cylinder(d = 5, h = 2, $fit = runFit);
>
> Provides the same opportunity to quickly amend all geometric constructions
> that use the runFit tolerance. This is particularly relevant to resizing as
> the ISO and ANSI standards reflect the reality that a 5mm hole requires a
> different tolerance than a 10mm hole to effect the same fit.
>
>
>
>
> >
> > Have you tried a similar method, defining named dimensions?
> >
> > One think I've started to do in my recent bigger projects is to break
> out dimensions and specific geometry modules into their own separate files:
> >
> > 0_dimensions.scad <named dimensions - for example
> m3_bolt_hole = 3.2; < this is where I do all tolerances
> etc.
> > 1_geometry.scad <for example Nema 17 mount pattern holes,
> as a 2D pattern
> > 2_component <say a 3D printed mount for the motor
> > 3_subassembly <say the mount with motor, screws, pulley
> etc
> > 4_majorassembly <say the whole axis
> > 5_render <the whole project for rendering.
>
> Yes, good idea. I think as our projects get more complex we all start
> creating a fistful of files… and I’m also hoping some day that OpenSCAD
> will allow for use, include and import to use non literal string values…
> but that’s another topic. :)
>
> >
> >
> > This has really helped me to improve version control and ease of
> navigation around complex projects - and made it easier to recycle code and
> incorporate scanned or downloaded parts.
> >
> > Cheers
> >
> > Alex Gibson
> >
> > admg consulting
> >
> > edumaker limited
> >
> > • Project management
> > • Operations & Process improvement
> > • 3D Printing
> >
> > -----Original Message-----
> > From: Discuss [mailto:discuss-bounces@lists.openscad.org] On Behalf Of
> Hugo Jackson
> > Sent: 29 October 2019 22:00
> > To: OpenSCAD general discussion
> > Subject: [OpenSCAD] Engineering Fits and Tolerance
> >
> > Has any thought been given to incorporating engineering fits and
> tolerances into OpenSCAD? As I understand it, OpenSCAD was originally
> conceived for the creation of STL files for a 3D printer and I’ve been
> thinking that the base functionality might be improved by a little more CAM
> in the CAD.
> >
> > For some time I’ve been using wrappers around most of the OpenSCAD
> modules in order to introduce engineering fits into the parts I create as
> 3d printers on the whole offer increasing precision and repeatability.
> >
> > Using a special variable $fit I can arbitrarily call up a module and it
> will adjust the the final size of the geometry according to the engineering
> fit I specify. e.g.
> >
> > cylinder(d = 5, h = 2, $fit = “g6”);
> >
> > I think anyone who has created interconnecting parts is familiar with
> the requirement to adjust for tolerance, but the core language as it stands
> requires this to be accomplished on a piecemeal basis, but to my way of
> thinking fit and tolerance are integral to the original purpose of OpenSCAD.
> >
> > I think this is particularly relevant as more and more users are
> acquiring machines that use different processes and that I might well wish
> to print a part on an FDM printer one day and a DLP the next, which I think
> would naturally call for a different fit specification.
> >
> > I also created some constants: kLeft, kRight, kFront, kBack, kTop &
> kBottom and use 6 element arrays to selectively apply tolerance, and use a
> special variable $faces to pass on that information as required:
> >
> > cube([7,3,8], $fit = “H11”, $faces = kLeft + kRight);
> >
> > And of course if I’m creating a project with lots of references to fit
> then I simply create an identifier for the fit, e.g.
> >
> > shaftFit = “h7”;
> >
> > So that if I move to a different type of machine where more or less
> tolerance is indicated, I only need to change the definition of shaftFit.
> >
> > I did some poking around in the mailing list archives and couldn’t see
> any reference to a discussion on this, but I’m sure it’s occurred to others
> before me, I just thought I’d ask where the community stands on
> incorporating this kind of functionality into the core language.
> >
> >
> > _______________________________________________
> > OpenSCAD mailing list
> > Discuss@lists.openscad.org
> > http://lists.openscad.org/mailman/listinfo/discuss_lists.openscad.org
> >
> >
> > _______________________________________________
> > OpenSCAD mailing list
> > Discuss@lists.openscad.org
> > http://lists.openscad.org/mailman/listinfo/discuss_lists.openscad.org
>
>
> _______________________________________________
> OpenSCAD mailing list
> Discuss@lists.openscad.org
> http://lists.openscad.org/mailman/listinfo/discuss_lists.openscad.org
>
HJ
Hugo Jackson
Thu, Oct 31, 2019 6:41 PM
On Oct 31, 2019, at 11:19 AM, nop head nop.head@gmail.com wrote:
I think you completely misunderstand what g6 tolerance means. It is isn't a clearance that you add to the nominal size and it certainly isn't 0.5mm.
A g6 5mm shaft has to be between 4.9960 and 4.9880mm. Good luck with that on a 3D printer with 0.2mm accuracy.
I beg to differ. :)
As I apologized in an earlier post, g6 was a poor choice to provide as an example for the 3D printing environment, and then I provided a more practical choice of g12 which for a 5mm shaft has a 4.876mm min and 4.996mm max providing a .12mm spread… which is a tolerance range I can achieve with most of my 3d printers.
And of course, g6, g12… they’re not the only fits available… ISO standards cover the precision of a wide range of manufacturing environments.
No engineer specifies greater precision than is required for the application at hand, simply for the reason that the rule of thumb is that the more precise a part needs to be, the more expensive it’s going to be, but by the same token, you can’t reasonably expect interlocking pieces to fit properly if no attention is paid to what the actual printed dimension of a part is going to be. I’m not saying it has to be accurate, I’m just suggesting that the precision should be predictable.
I’m not saying that specifying tolerances a 3D printer is totally incapable of producing is going to somehow make a 3D printer a more precise machine, what I am saying is that by adopting a system of standardized tolerances would be a positive and useful endeavour. So okay, a printer owner can’t hold a g6 or a g12 tolerance… but the question is, what kind of tolerance CAN they achieve and as a consequence, what classification of fits are appropriate for 3D modellers who are designing parts for production on an FDM machine.
On Oct 31, 2019, at 4:28 AM, Alex Gibson <alex@alexgibson.net mailto:alex@alexgibson.net> wrote:
Going back to your original question Hugh, and your example:
cylinder(d = 5, h = 2, $fit = “g6”);
The way I've seen a lot of machine parts (usually 3D printer) programmed in OpenSCAD is this:
cylinder(d = g6, h = 2);
...and above this at the top of the file...
fit_tolerance = 0.5;
machine_tolerance = 0.2;
g6 = 5+fit_tolerance+machine_tolerance;
Rather than being 'piecemeal' I think building up layers of tolerance like this can be very helpful and reduce confusion and repetitive typing within the body of your design code. Every time you want that size hole in your project, you just use d= g6 by name. You can tune the tolerances after the initial design without re-coding.
The idea of a global $fit variable seems nice, but you would have to have it associated with a big table which defines what g6 and many other tolerances are, which you'd need to remember as you are designing the part. Also it could not take into account multiple fudge factors, and to me that's the real beauty of OpenSCAD for this sort of thing.
A very big table is exactly what I have,,, and it’s the table lookup and syntax parsing that would be nice to have handled faster and more efficiently by the core.
I guess it just comes down to personal style and one’s personal understanding of the OpenSCAD zeit. I think much is made of OpenSCAD’s parametric ability for resizing and substitution of dimensions and as different printing methodologies start being added, I think that the OpenSCAD core would benefit with a nod to ‘parametric’ tolerance.
In the example you sight, you identify g6 as a calculation involving the nominal dimensions, the fit tolerance and the machine tolerance… and to my way of thinking what’s going on would be clearer and more easily amended with the scheme I use… rather than:
fit_tolerance = 0.5;
machine_tolerance = 0.2;
g6 = 5+fit_tolerance+machine_tolerance;
I think:
cylinder(d = 5, h = 2, $fit = “g6”);
Is more straightforward, particularly if one declares the fit itself as a value, such as:
runFit = “g6”;
And so:
cylinder(d = 5, h = 2, $fit = runFit);
Provides the same opportunity to quickly amend all geometric constructions that use the runFit tolerance. This is particularly relevant to resizing as the ISO and ANSI standards reflect the reality that a 5mm hole requires a different tolerance than a 10mm hole to effect the same fit.
Have you tried a similar method, defining named dimensions?
One think I've started to do in my recent bigger projects is to break out dimensions and specific geometry modules into their own separate files:
0_dimensions.scad <named dimensions - for example m3_bolt_hole = 3.2; < this is where I do all tolerances etc.
1_geometry.scad <for example Nema 17 mount pattern holes, as a 2D pattern
2_component <say a 3D printed mount for the motor
3_subassembly <say the mount with motor, screws, pulley etc
4_majorassembly <say the whole axis
5_render <the whole project for rendering.
Yes, good idea. I think as our projects get more complex we all start creating a fistful of files… and I’m also hoping some day that OpenSCAD will allow for use, include and import to use non literal string values… but that’s another topic. :)
This has really helped me to improve version control and ease of navigation around complex projects - and made it easier to recycle code and incorporate scanned or downloaded parts.
Cheers
Alex Gibson
admg consulting
edumaker limited
• Project management
• Operations & Process improvement
• 3D Printing
-----Original Message-----
From: Discuss [mailto:discuss-bounces@lists.openscad.org mailto:discuss-bounces@lists.openscad.org] On Behalf Of Hugo Jackson
Sent: 29 October 2019 22:00
To: OpenSCAD general discussion
Subject: [OpenSCAD] Engineering Fits and Tolerance
Has any thought been given to incorporating engineering fits and tolerances into OpenSCAD? As I understand it, OpenSCAD was originally conceived for the creation of STL files for a 3D printer and I’ve been thinking that the base functionality might be improved by a little more CAM in the CAD.
For some time I’ve been using wrappers around most of the OpenSCAD modules in order to introduce engineering fits into the parts I create as 3d printers on the whole offer increasing precision and repeatability.
Using a special variable $fit I can arbitrarily call up a module and it will adjust the the final size of the geometry according to the engineering fit I specify. e.g.
cylinder(d = 5, h = 2, $fit = “g6”);
I think anyone who has created interconnecting parts is familiar with the requirement to adjust for tolerance, but the core language as it stands requires this to be accomplished on a piecemeal basis, but to my way of thinking fit and tolerance are integral to the original purpose of OpenSCAD.
I think this is particularly relevant as more and more users are acquiring machines that use different processes and that I might well wish to print a part on an FDM printer one day and a DLP the next, which I think would naturally call for a different fit specification.
I also created some constants: kLeft, kRight, kFront, kBack, kTop & kBottom and use 6 element arrays to selectively apply tolerance, and use a special variable $faces to pass on that information as required:
cube([7,3,8], $fit = “H11”, $faces = kLeft + kRight);
And of course if I’m creating a project with lots of references to fit then I simply create an identifier for the fit, e.g.
shaftFit = “h7”;
So that if I move to a different type of machine where more or less tolerance is indicated, I only need to change the definition of shaftFit.
I did some poking around in the mailing list archives and couldn’t see any reference to a discussion on this, but I’m sure it’s occurred to others before me, I just thought I’d ask where the community stands on incorporating this kind of functionality into the core language.
OpenSCAD mailing list
Discuss@lists.openscad.org mailto:Discuss@lists.openscad.org
http://lists.openscad.org/mailman/listinfo/discuss_lists.openscad.org http://lists.openscad.org/mailman/listinfo/discuss_lists.openscad.org
OpenSCAD mailing list
Discuss@lists.openscad.org mailto:Discuss@lists.openscad.org
http://lists.openscad.org/mailman/listinfo/discuss_lists.openscad.org http://lists.openscad.org/mailman/listinfo/discuss_lists.openscad.org
> On Oct 31, 2019, at 11:19 AM, nop head <nop.head@gmail.com> wrote:
>
> I think you completely misunderstand what g6 tolerance means. It is isn't a clearance that you add to the nominal size and it certainly isn't 0.5mm.
>
> A g6 5mm shaft has to be between 4.9960 and 4.9880mm. Good luck with that on a 3D printer with 0.2mm accuracy.
>
I beg to differ. :)
As I apologized in an earlier post, g6 was a poor choice to provide as an example for the 3D printing environment, and then I provided a more practical choice of g12 which for a 5mm shaft has a 4.876mm min and 4.996mm max providing a .12mm spread… which is a tolerance range I can achieve with most of my 3d printers.
And of course, g6, g12… they’re not the only fits available… ISO standards cover the precision of a wide range of manufacturing environments.
No engineer specifies greater precision than is required for the application at hand, simply for the reason that the rule of thumb is that the more precise a part needs to be, the more expensive it’s going to be, but by the same token, you can’t reasonably expect interlocking pieces to fit properly if no attention is paid to what the actual printed dimension of a part is going to be. I’m not saying it has to be accurate, I’m just suggesting that the precision should be predictable.
I’m not saying that specifying tolerances a 3D printer is totally incapable of producing is going to somehow make a 3D printer a more precise machine, what I am saying is that by adopting a system of standardized tolerances would be a positive and useful endeavour. So okay, a printer owner can’t hold a g6 or a g12 tolerance… but the question is, what kind of tolerance CAN they achieve and as a consequence, what classification of fits are appropriate for 3D modellers who are designing parts for production on an FDM machine.
> On Thu, 31 Oct 2019 at 18:05, Hugo Jackson <hugo@apres.net <mailto:hugo@apres.net>> wrote:
>
> > On Oct 31, 2019, at 4:28 AM, Alex Gibson <alex@alexgibson.net <mailto:alex@alexgibson.net>> wrote:
> >
> > Going back to your original question Hugh, and your example:
> > cylinder(d = 5, h = 2, $fit = “g6”);
> >
> > The way I've seen a lot of machine parts (usually 3D printer) programmed in OpenSCAD is this:
> >
> > cylinder(d = g6, h = 2);
> >
> > ...and above this at the top of the file...
> > fit_tolerance = 0.5;
> > machine_tolerance = 0.2;
> > g6 = 5+fit_tolerance+machine_tolerance;
> >
> > Rather than being 'piecemeal' I think building up layers of tolerance like this can be very helpful and reduce confusion and repetitive typing within the body of your design code. Every time you want that size hole in your project, you just use d= g6 by name. You can tune the tolerances after the initial design without re-coding.
> >
> > The idea of a global $fit variable seems nice, but you would have to have it associated with a big table which defines what g6 and many other tolerances are, which you'd need to remember as you are designing the part. Also it could not take into account multiple fudge factors, and to me that's the real beauty of OpenSCAD for this sort of thing.
>
> A very big table is exactly what I have,,, and it’s the table lookup and syntax parsing that would be nice to have handled faster and more efficiently by the core.
>
> I guess it just comes down to personal style and one’s personal understanding of the OpenSCAD zeit. I think much is made of OpenSCAD’s parametric ability for resizing and substitution of dimensions and as different printing methodologies start being added, I think that the OpenSCAD core would benefit with a nod to ‘parametric’ tolerance.
>
> In the example you sight, you identify g6 as a calculation involving the nominal dimensions, the fit tolerance and the machine tolerance… and to my way of thinking what’s going on would be clearer and more easily amended with the scheme I use… rather than:
>
> >> fit_tolerance = 0.5;
> >> machine_tolerance = 0.2;
> >> g6 = 5+fit_tolerance+machine_tolerance;
>
> > cylinder(d = g6, h = 2);
>
> I think:
>
> cylinder(d = 5, h = 2, $fit = “g6”);
>
> Is more straightforward, particularly if one declares the fit itself as a value, such as:
>
> runFit = “g6”;
>
> And so:
>
> cylinder(d = 5, h = 2, $fit = runFit);
>
> Provides the same opportunity to quickly amend all geometric constructions that use the runFit tolerance. This is particularly relevant to resizing as the ISO and ANSI standards reflect the reality that a 5mm hole requires a different tolerance than a 10mm hole to effect the same fit.
>
>
>
>
> >
> > Have you tried a similar method, defining named dimensions?
> >
> > One think I've started to do in my recent bigger projects is to break out dimensions and specific geometry modules into their own separate files:
> >
> > 0_dimensions.scad <named dimensions - for example m3_bolt_hole = 3.2; < this is where I do all tolerances etc.
> > 1_geometry.scad <for example Nema 17 mount pattern holes, as a 2D pattern
> > 2_component <say a 3D printed mount for the motor
> > 3_subassembly <say the mount with motor, screws, pulley etc
> > 4_majorassembly <say the whole axis
> > 5_render <the whole project for rendering.
>
> Yes, good idea. I think as our projects get more complex we all start creating a fistful of files… and I’m also hoping some day that OpenSCAD will allow for use, include and import to use non literal string values… but that’s another topic. :)
>
> >
> >
> > This has really helped me to improve version control and ease of navigation around complex projects - and made it easier to recycle code and incorporate scanned or downloaded parts.
> >
> > Cheers
> >
> > Alex Gibson
> >
> > admg consulting
> >
> > edumaker limited
> >
> > • Project management
> > • Operations & Process improvement
> > • 3D Printing
> >
> > -----Original Message-----
> > From: Discuss [mailto:discuss-bounces@lists.openscad.org <mailto:discuss-bounces@lists.openscad.org>] On Behalf Of Hugo Jackson
> > Sent: 29 October 2019 22:00
> > To: OpenSCAD general discussion
> > Subject: [OpenSCAD] Engineering Fits and Tolerance
> >
> > Has any thought been given to incorporating engineering fits and tolerances into OpenSCAD? As I understand it, OpenSCAD was originally conceived for the creation of STL files for a 3D printer and I’ve been thinking that the base functionality might be improved by a little more CAM in the CAD.
> >
> > For some time I’ve been using wrappers around most of the OpenSCAD modules in order to introduce engineering fits into the parts I create as 3d printers on the whole offer increasing precision and repeatability.
> >
> > Using a special variable $fit I can arbitrarily call up a module and it will adjust the the final size of the geometry according to the engineering fit I specify. e.g.
> >
> > cylinder(d = 5, h = 2, $fit = “g6”);
> >
> > I think anyone who has created interconnecting parts is familiar with the requirement to adjust for tolerance, but the core language as it stands requires this to be accomplished on a piecemeal basis, but to my way of thinking fit and tolerance are integral to the original purpose of OpenSCAD.
> >
> > I think this is particularly relevant as more and more users are acquiring machines that use different processes and that I might well wish to print a part on an FDM printer one day and a DLP the next, which I think would naturally call for a different fit specification.
> >
> > I also created some constants: kLeft, kRight, kFront, kBack, kTop & kBottom and use 6 element arrays to selectively apply tolerance, and use a special variable $faces to pass on that information as required:
> >
> > cube([7,3,8], $fit = “H11”, $faces = kLeft + kRight);
> >
> > And of course if I’m creating a project with lots of references to fit then I simply create an identifier for the fit, e.g.
> >
> > shaftFit = “h7”;
> >
> > So that if I move to a different type of machine where more or less tolerance is indicated, I only need to change the definition of shaftFit.
> >
> > I did some poking around in the mailing list archives and couldn’t see any reference to a discussion on this, but I’m sure it’s occurred to others before me, I just thought I’d ask where the community stands on incorporating this kind of functionality into the core language.
> >
> >
> > _______________________________________________
> > OpenSCAD mailing list
> > Discuss@lists.openscad.org <mailto:Discuss@lists.openscad.org>
> > http://lists.openscad.org/mailman/listinfo/discuss_lists.openscad.org <http://lists.openscad.org/mailman/listinfo/discuss_lists.openscad.org>
> >
> >
> > _______________________________________________
> > OpenSCAD mailing list
> > Discuss@lists.openscad.org <mailto:Discuss@lists.openscad.org>
> > http://lists.openscad.org/mailman/listinfo/discuss_lists.openscad.org <http://lists.openscad.org/mailman/listinfo/discuss_lists.openscad.org>
>
>
> _______________________________________________
> OpenSCAD mailing list
> Discuss@lists.openscad.org <mailto:Discuss@lists.openscad.org>
> http://lists.openscad.org/mailman/listinfo/discuss_lists.openscad.org <http://lists.openscad.org/mailman/listinfo/discuss_lists.openscad.org>
> _______________________________________________
> OpenSCAD mailing list
> Discuss@lists.openscad.org
> http://lists.openscad.org/mailman/listinfo/discuss_lists.openscad.org
