On Monday 30 August 2021 11:21:51 nop head wrote:

The nozzle radius has no effect on the object dimensions. What matters
is the volume of plastic flowing through it.

Do you not get a nozzle dia oversize when you are driving the nozzles
center x distance? It is not and never can be a point src when it
is .4mm in diameter. So if I drive it exactly a mm, I will have -.2 at
the start of that mm. and a +.2mm at the end, for a 1.4mm total length.

The slicer is supposed to know that based on the nozzle dia and
compensate but the success of that is highly dependent on the flow,
which if way off, can exceed 2mm in width for the laid down line even if
its only .19mm thick.  With this printer, the initial prime on the edge
of the build plate as it starts is nearly 3mm wide using the default
preamble in cura. I have cut that by 50%, but still get that initial
line nearly 2mm wide. And that I am positive, contributes a lot to the
plastic buildup on the nozzle that will pull a pat loose and waste it.
Several times I have lost a print, and had to clean a 50 cent coin
diameter

Using a .19 layer, its now around 6mm up on that 100x100y50z test file.
It did one of the splines at 90% flow this morning, showing 5.99mm up as
it parked, but the part measures 6.72mm tall.

I'll know more when this is done, a bit over an hour from now.

Once thats fixed, then I'll do a temp tower to see if I can stop the
bridging. By then it will be close to time for another spool, and start
all over. Need 10 kg spools and driers to fit them... :-)

Thank you nop head.

On Mon, 30 Aug 2021 at 15:28, Gene Heskett gheskett@shentel.net
wrote:

On Sunday 29 August 2021 03:47:09 Gene Heskett wrote:

On Saturday 28 August 2021 23:21:21 MichaelAtOz wrote:

Calibration is something you need to do, not the printer.

You need to slice & print calibration objects and get your
callipers out.

Then adjust slicer settings, rinse, repeat, until you get
physical objects matching the specification of the calibration
object.

You will need to have profiles for different materials with
settings from a calibration run for that material (usually just
extruder settings being different).

I haven't calibrated for a long time as I use Shapeways, but
Google coughed up these which look reasonable.

Yes, I dl'd several of them, should be helpfull, thank you.

https://all3dp.com/2/how-to-calibrate-a-3d-printer-simply-explai
ned/

Then do some torture tests

https://all3dp.com/2/best-3d-printer-test-print-3d-models/

I am preparing to print 1 or two of what I have dl'd from the links
above and below, but first I thought I'd see what happens to a
priint by fiddling with temps and flows. Flow in particular seems to
be excessive. so as a test, using the printers builtin first layer
calibration. adjusted it for an initial single line thickness of
.19mm, but the solid pad at the end of that pattern was .25 to .27
thick, so I repeated that but at 90% flow from the printers tune
menu, and got a final pad .21mm thick that when microscoped, was
still nicely welded to the adjacent line, but the top surface felt a
lot smoother, so I have it doing one of the spline parts, and its
looking cleaner about half done than previous copies have.  Then
I'll do that 100mmX,100mmY,50mmZ thingy. Big enough to separate
scaling errors from nozzle radius errors.

There is little point printing functional objects until you can
print a calibration object accurately.

https://www.thingiverse.com/search?q=calibration
https://www.thingiverse.com/search?q=calibration&type=things
&type=things

---

From: Father Horton [mailto:fatherhorton@gmail.com]
Sent: Sun, 29 Aug 2021 12:36
To: OpenSCAD general discussion
Subject: [OpenSCAD] Re: Provide a simple measurement tool

It almost sounds as if your printer profile is messed up. Are
you using defaults in PrusaSlicer, or did you change something,
or are you using Cura?

On Sat, Aug 28, 2021 at 9:24 PM Gene Heskett
gheskett@shentel.net wrote:

On Saturday 28 August 2021 20:51:21 Gareth Chen wrote:

If your printer is printing 5.98mm parts to be 6.51mm tall
it's seriously out of calibration...

Its a Prusa mk3S, has about a 25 minute calibration using
markers on the bed for xy references. But other that running z
against to top stops and hammering on the top for a while, I
don't see where it calibrates the z range. XY home apparently
senses motor current to detect just touching the left and rear
stops. Not even hard enough to obviously hear it hit. If the
same circuit is used for detecting the top of travel, then its
failing as its dual z motors and useing a default because it
hammers the top of travel for about a full second. I'll ask
prusa monday. And get the m command to change it too.

Thank you..
[...]
Cheers, Gene Heskett

"There are four boxes to be used in defense of liberty:
soap, ballot, jury, and ammo. Please use in that order."
-Ed Howdershelt (Author)
If we desire respect for the law, we must first make the law
respectable. - Louis D. Brandeis
Genes Web page http://geneslinuxbox.net:6309/gene

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Cheers, Gene Heskett

Cheers, Gene Heskett

"There are four boxes to be used in defense of liberty:
soap, ballot, jury, and ammo. Please use in that order."
-Ed Howdershelt (Author)
If we desire respect for the law, we must first make the law
respectable. - Louis D. Brandeis
Genes Web page http://geneslinuxbox.net:6309/gene

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Cheers, Gene Heskett

"There are four boxes to be used in defense of liberty:
soap, ballot, jury, and ammo. Please use in that order."
-Ed Howdershelt (Author)
If we desire respect for the law, we must first make the law respectable.

• Louis D. Brandeis
  Genes Web page http://geneslinuxbox.net:6309/gene

OpenSCAD mailing list
To unsubscribe send an email to discuss-leave@lists.openscad.org

On 8/29/2021 5:57 PM, Adrian Mariano wrote:

The question I have is: why do you need to know where a point is?  What
are you trying to do that requires this knowledge in a real model?  I
wonder if there might be alternative approaches that don't require that
information, or where the model can be structured so that it's easy to know
where the point is.  I suspect that at least some of the time, such
alternative approaches may exist.

I think the problem with straight "calculation" schemes is that they can
get very hard, very fast.

Quick, what's the distance between the closest points in these squares?

rotate(a) square(10);
translate([20,20]) rotate(b) square(10);

You're a much stronger math guy than I am, so maybe you can do that off
the top of your head, but it would take me some pretty serious thinking.
And that's a simple case.

In a real project... as I've mentioned, a lot of my work is in scale
models.  I was designing an armchair:
[image:
https://cdn.thingiverse.com/assets/ed/00/42/d1/65/featured_preview_WIN_20200407_22_06_02_Pro.jpg]

Here's what generates the sides and arms:

     // Sides
     for (s=[-1, 1]) {
         translate([s*w/2, d, leg_h+seat_h]) {
             rotate([90, 0, -90])
                 clip(v=[0,0,s]) {
                     pipe_polygon(r=wing_t, fill=true, open=true, [
                         [3*inch, 0],
                         [18*inch, 0],
                         [18*inch, 8.5*inch],
                         [4*inch, 8.5*inch],
                         [3.5*inch, 17*inch],
                         [4*inch, 26*inch],
                         [-3.8*inch, 28*inch]
                     ]);
                 }
             // Arms
             translate([s*0*inch, -20.75*inch, 8.75*inch])
                 rotate([-86.5,0,4*s])
                 cylinder(d2=wing_t*1.3, d1=wing_t*2, h=16*inch);
         }
     }

All of those dimensions are measured by hand off the real object, and the
angles are eyeballed.

Now, what's the width, measured between the outsides of the two arms?  I
want to tweak the angles and sizes so that's it's pretty close to correct.

But your examples also gets at the question of what allowed
definitions of points are, the "random" points.  Your definitions both
have to do with optimization, which means you've gone up a leap in
complexity from simple geometry.  Points derived from optimization
aren't going to be clickable on a model.  You can't "see" them.  The
only way you can find these points is by doing the math. 

I can't run your model because it's full of parameters.  But I would
think that in that case, at least, it would be possible to define your
model in terms of the width.   If you start from the width and build
everything from there then you'll have the right width. 

That's the kind of thing I meant when I wondered about the need for
access to distance values.  The notion that you need to know the width
of your model after the fact so you can fix your botched model by
trial and error to make it the right width....doesn't appeal to me as
a design strategy.  But if you really want to pursue trial-and-error
design then having a way to measure does seem very important.  (It's
unclear to me if starting from the width just shifts the measurement
problem somewhere else, but it seems like if you have measurable
parameters you should be able to measure them and then design to the
measurements directly.) 

Prusaslicer defaults compensate pretty well for dimensions. My small
holes are a bit tight, but I’m usually drilling and tapping those so I
haven’t tried to optimize them. Generally all I tweak per spool is
extruder flow, which I often run at about 95%. I mostly print PETG.
Plastic repelling paint on the extruder helps with stringing. I’m
using a hardened 0.4 nozzle at 270 deg C.

Prusaslicer defaults compensate pretty well for dimensions. My small
holes are a bit tight, but I’m usually drilling and tapping those so I
haven’t tried to optimize them. Generally all I tweak per spool is
extruder flow, which I often run at about 95%. I mostly print PETG.
Plastic repelling paint on the extruder helps with stringing. I’m
using a hardened 0.4 nozzle at 270 deg C.

On Monday 30 August 2021 14:41:31 David Gustavson wrote:

Prusaslicer defaults compensate pretty well for dimensions. My small
holes are a bit tight, but I’m usually drilling and tapping those so I
haven’t tried to optimize them. Generally all I tweak per spool is
extruder flow, which I often run at about 95%. I mostly print PETG.
Plastic repelling paint on the extruder helps with stringing. I’m
using a hardened 0.4 nozzle at 270 deg C.

I haven't tried it that hot YET, but the temp tower I just did would seem
to indicate more heat than 240C might be beneficial. At 95% flow, no
bridges were usable, yet it slobbers all over the internal facing
splines. I'm going to try one of them at 250C/85C, wide open fan after
the first layer.

The 100X100Y50Z test was within .2mm everyplace. 50mm tall leg was
50.07mm.

So why is my 5.98mm tall gear, 6.72mm tall when miked. 3/4mm taller than
designed?

Cheers, Gene Heskett

"There are four boxes to be used in defense of liberty:
soap, ballot, jury, and ammo. Please use in that order."
-Ed Howdershelt (Author)
If we desire respect for the law, we must first make the law respectable.

• Louis D. Brandeis
  Genes Web page http://geneslinuxbox.net:6309/gene

OpenSCAD mailing list
To unsubscribe send an email to discuss-leave@lists.openscad.org

Do you not get a nozzle dia oversize when you are driving the nozzles

That technique has advantages, but it also has serious weaknesses:

• It can't measure the distance between points on two sibling
  objects, because of the "black hole" effect.  (You can echo
  coordinates out to the log and then externally do math on them,
  but bleah.)
• It has no direct way to measure from anything but the origin. 
  Measuring against simple objects like cubes is easy math. 
  Measuring the height of a cylinder is easy.  Measuring from a
  particular point on the perimeter of a circle is not too bad. 
  Measuring between the two closest points of two circles starts to
  get ugly.  Measuring anything non-trivial involving boolean
  operations gets hard.

@GeneHeskett The mechanical Z tolerances can't be that far off.
Somehow a wrong value has gotten put in the code relating steps to Z,
I suspect. Look at the G code's Z values!

I had to raise my temperature from about 240 to 270 after switching
from a brass nozzle to the hardened one, which conducts heat less
well. I also changed to a solid copper heat block, just on
superstition.

Do I recall you use Cura on your Prusa? Cura has some plugins I'd like
to try, but I've been afraid to use it.