Question about gear library
I am trying to model a gear for an Atlas metal lathe. I have some original
(real-life) gears, but want to print one with a different number of teeth.
I have found this gear library by GregFrost:
https://www.thingiverse.com/thing:3575/files
I know that this list is not responsible for the library, but it seems to
be a good one, and I am hoping someone here can help.
My question is about the units of the input parameters. For example, in
the file parametric_involute_gear_v5.0.scad there are some example gears.
I modified one slightly as follows:
gear (number_of_teeth=64,
circular_pitch=285.0,
circles=0);
I chose the value for circular_pitch experimentally. First I put an Echo()
statement in the gear_shape module such that it reports the minor diameter,
pitch diameter, and major diameter (in mm). I then slowly modified the
circular_pitch value until it matched the measurements of my actual
real-life gear, taken with my micrometer.
I am confused about what circular_pitch is supposed to represent. I
reviewed standard gear terms from here:
https://en.wikipedia.org/wiki/List_of_gear_nomenclature#Circular_Pitch
Circular pitch should be the distance (in mm) from tooth to tooth. In my
actual real-life gear, the value is about 5 mm.
On a slightly different tact, I am also confused about gear terminology
used for my lathe. The gears are typically described using inches and
diametral pitch (which is supposed to be 1/circular_pitch). According to
this site:
https://www.practicalmachinist.com/vb/general/need-atlas-lathe-gear-208658/
(which references here: http://www.lathes.co.uk/atlas/), Atlas gears use a
16DP, which I think means 16 diametral pitch or 16 teeth per inch. I'm not
sure I believe this number, because my real-life gear with 20 teeth has a
diameter of 1.475 inches, circumference of ~4.3 inches, and thus 20/4.3 =
~4.6 teeth/inch.
Summary:
- Can anyone help me understand the units for the circular_pitch
parameter in the gear() module as described above? - Can anyone see the source of my confusion about the 16DP
Thanks in advance,
Kevin T
I am not familiar with Greg's library but DP is not about circumference. It
is the number of teeth per inch of its pitch diameter, an odd measure that
doesn't really have a physical meaning because the teeth go around the
circumference, not across the diameter.
Also the pitch diameter is not the outside diameter, it is the diameter
where the teeth mesh, sort of half way down the tooth. So you can mesh two
gears if they have the same DP and you space them apart by half the sum of
the pitch diameters.
I have a vague memory that Greg's library has a bug in the way
circular_pitch is used.
On Sat, 22 Dec 2018 at 13:16, Kevin Toppenberg kdtop3@gmail.com wrote:
I am trying to model a gear for an Atlas metal lathe. I have some
original (real-life) gears, but want to print one with a different number
of teeth.
I have found this gear library by GregFrost:
https://www.thingiverse.com/thing:3575/files
I know that this list is not responsible for the library, but it seems to
be a good one, and I am hoping someone here can help.
My question is about the units of the input parameters. For example, in
the file parametric_involute_gear_v5.0.scad there are some example gears.
I modified one slightly as follows:
gear (number_of_teeth=64,
circular_pitch=285.0,
circles=0);
I chose the value for circular_pitch experimentally. First I put an
Echo() statement in the gear_shape module such that it reports the minor
diameter, pitch diameter, and major diameter (in mm). I then slowly
modified the circular_pitch value until it matched the measurements of my
actual real-life gear, taken with my micrometer.
I am confused about what circular_pitch is supposed to represent. I
reviewed standard gear terms from here:
https://en.wikipedia.org/wiki/List_of_gear_nomenclature#Circular_Pitch
Circular pitch should be the distance (in mm) from tooth to tooth. In my
actual real-life gear, the value is about 5 mm.
On a slightly different tact, I am also confused about gear terminology
used for my lathe. The gears are typically described using inches and
diametral pitch (which is supposed to be 1/circular_pitch). According to
this site:
https://www.practicalmachinist.com/vb/general/need-atlas-lathe-gear-208658/
(which references here: http://www.lathes.co.uk/atlas/), Atlas gears use
a 16DP, which I think means 16 diametral pitch or 16 teeth per inch. I'm
not sure I believe this number, because my real-life gear with 20 teeth has
a diameter of 1.475 inches, circumference of ~4.3 inches, and thus 20/4.3 =
~4.6 teeth/inch.
Summary:
1. Can anyone help me understand the units for the circular_pitch
parameter in the gear() module as described above?
2. Can anyone see the source of my confusion about the 16DP
Thanks in advance,
Kevin T
OpenSCAD mailing list
Discuss@lists.openscad.org
http://lists.openscad.org/mailman/listinfo/discuss_lists.openscad.org
Hi, I’ve used Greg’s excellent library a lot without ever getting into the fine detail of this – I’m wondering why you actually need to?
My assumption is that you might be trying to change only one gear of a pair?
If you can change both gears, then you don’t need to worry much about the pitches – simply specify the distance between shafts and the gear ratio, and Greg’s library will take care of it all very nicely.
If you’re hoping to keep using one of the gears, you will need to much more deeply understand the pitches, or if your main motivation is to understand how Greg’s library is doing its job, please ignore this useless intervention!
Cheers,
Alex Gibson
admg consulting
edumaker limited
· Project management
· Operations & Process improvement
· 3D Printing
From: Discuss [mailto:discuss-bounces@lists.openscad.org] On Behalf Of nop head
Sent: 22 December 2018 13:52
To: OpenSCAD general discussion
Subject: Re: [OpenSCAD] Question about gear library
I am not familiar with Greg's library but DP is not about circumference. It is the number of teeth per inch of its pitch diameter, an odd measure that doesn't really have a physical meaning because the teeth go around the circumference, not across the diameter.
Also the pitch diameter is not the outside diameter, it is the diameter where the teeth mesh, sort of half way down the tooth. So you can mesh two gears if they have the same DP and you space them apart by half the sum of the pitch diameters.
I have a vague memory that Greg's library has a bug in the way circular_pitch is used.
On Sat, 22 Dec 2018 at 13:16, Kevin Toppenberg kdtop3@gmail.com wrote:
I am trying to model a gear for an Atlas metal lathe. I have some original (real-life) gears, but want to print one with a different number of teeth.
I have found this gear library by GregFrost: https://www.thingiverse.com/thing:3575/files
I know that this list is not responsible for the library, but it seems to be a good one, and I am hoping someone here can help.
My question is about the units of the input parameters. For example, in the file parametric_involute_gear_v5.0.scad there are some example gears. I modified one slightly as follows:
gear (number_of_teeth=64,
circular_pitch=285.0,
circles=0);
I chose the value for circular_pitch experimentally. First I put an Echo() statement in the gear_shape module such that it reports the minor diameter, pitch diameter, and major diameter (in mm). I then slowly modified the circular_pitch value until it matched the measurements of my actual real-life gear, taken with my micrometer.
I am confused about what circular_pitch is supposed to represent. I reviewed standard gear terms from here: https://en.wikipedia.org/wiki/List_of_gear_nomenclature#Circular_Pitch
Circular pitch should be the distance (in mm) from tooth to tooth. In my actual real-life gear, the value is about 5 mm.
On a slightly different tact, I am also confused about gear terminology used for my lathe. The gears are typically described using inches and diametral pitch (which is supposed to be 1/circular_pitch). According to this site: https://www.practicalmachinist.com/vb/general/need-atlas-lathe-gear-208658/ (which references here: http://www.lathes.co.uk/atlas/), Atlas gears use a 16DP, which I think means 16 diametral pitch or 16 teeth per inch. I'm not sure I believe this number, because my real-life gear with 20 teeth has a diameter of 1.475 inches, circumference of ~4.3 inches, and thus 20/4.3 = ~4.6 teeth/inch.
Summary:
- Can anyone help me understand the units for the circular_pitch parameter in the gear() module as described above?
- Can anyone see the source of my confusion about the 16DP
Thanks in advance,
Kevin T
OpenSCAD mailing list
Discuss@lists.openscad.org
http://lists.openscad.org/mailman/listinfo/discuss_lists.openscad.org
If you know the diametral pitch of a gear train you should be in pretty good shape as you can work backwards to determining the pitch diameter and other necessary dimensions.
As others have noted, diametral pitch is the distance between gear teeth, but this is not measured at the outer diameter of the gear but at a calculated point between the outer diameter of the gear teeth and the diameter of the base of the teeth, and this is know as the pitch circle or reference diameter.
pitchDiameter = numberOfTeeth / diametralPitch;
So if you want to calculate the pitch diameter for Greg’s routines you can just count the teeth on the gear you are trying to copy and plug that into the formula above. If Atlas gears do have a diametral pitch of 16 and you count the number of teeth accurately :) then you’re gonna end up with a gear the correct size.
If you want to check that against what you’ve measured as the outside diameter of your gear you can do the following, noting that the dimension between the pitchDiameter and the outside diameter is called the addendum
addendum = 1 / diametralPitch;
outsideDiameter = pitchDiameter + (2 * addendum);
Looking at the link you posted (https://www.practicalmachinist.com/vb/general/need-atlas-lathe-gear-208658/ https://www.practicalmachinist.com/vb/general/need-atlas-lathe-gear-208658/ ) it mentions that atlas gears use a 14.5 degree pressure angle so in addition to the routine in Greg’s library you’re already calling you’ll want to include the pressure_angle parameter as well, as the default of 20 is not what you want., e.g.
gear (number_of_teeth=64,
// circular_pitch=285.0, // call greg’s routine with the diametral pitch parameter.. not circular pitch
diametral_pitch = 16,
pressure_angle = 14.5,
circles=0);
Hope this is helpful.
On Dec 22, 2018, at 1:52 PM, nop head nop.head@gmail.com wrote:
I am not familiar with Greg's library but DP is not about circumference. It is the number of teeth per inch of its pitch diameter, an odd measure that doesn't really have a physical meaning because the teeth go around the circumference, not across the diameter.
Also the pitch diameter is not the outside diameter, it is the diameter where the teeth mesh, sort of half way down the tooth. So you can mesh two gears if they have the same DP and you space them apart by half the sum of the pitch diameters.
I have a vague memory that Greg's library has a bug in the way circular_pitch is used.
On Sat, 22 Dec 2018 at 13:16, Kevin Toppenberg <kdtop3@gmail.com mailto:kdtop3@gmail.com> wrote:
I am trying to model a gear for an Atlas metal lathe. I have some original (real-life) gears, but want to print one with a different number of teeth.
I have found this gear library by GregFrost: https://www.thingiverse.com/thing:3575/files https://www.thingiverse.com/thing:3575/files
I know that this list is not responsible for the library, but it seems to be a good one, and I am hoping someone here can help.
My question is about the units of the input parameters. For example, in the file parametric_involute_gear_v5.0.scad there are some example gears. I modified one slightly as follows:
gear (number_of_teeth=64,
circular_pitch=285.0,
circles=0);
I chose the value for circular_pitch experimentally. First I put an Echo() statement in the gear_shape module such that it reports the minor diameter, pitch diameter, and major diameter (in mm). I then slowly modified the circular_pitch value until it matched the measurements of my actual real-life gear, taken with my micrometer.
I am confused about what circular_pitch is supposed to represent. I reviewed standard gear terms from here: https://en.wikipedia.org/wiki/List_of_gear_nomenclature#Circular_Pitch https://en.wikipedia.org/wiki/List_of_gear_nomenclature#Circular_Pitch
Circular pitch should be the distance (in mm) from tooth to tooth. In my actual real-life gear, the value is about 5 mm.
On a slightly different tact, I am also confused about gear terminology used for my lathe. The gears are typically described using inches and diametral pitch (which is supposed to be 1/circular_pitch). According to this site: https://www.practicalmachinist.com/vb/general/need-atlas-lathe-gear-208658/ https://www.practicalmachinist.com/vb/general/need-atlas-lathe-gear-208658/ (which references here: http://www.lathes.co.uk/atlas/ http://www.lathes.co.uk/atlas/), Atlas gears use a 16DP, which I think means 16 diametral pitch or 16 teeth per inch. I'm not sure I believe this number, because my real-life gear with 20 teeth has a diameter of 1.475 inches, circumference of ~4.3 inches, and thus 20/4.3 = ~4.6 teeth/inch.
Summary:
Can anyone help me understand the units for the circular_pitch parameter in the gear() module as described above?
Can anyone see the source of my confusion about the 16DP
Thanks in advance,
Kevin T
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
Hi Kevin,
As others have pointed out Circular pitch means something slightly different and direct measurement is difficult (also pressure angle)..
I suggest looking at the links in this reference:
- https://github.com/jnweiger/inkscape-gears-dev
This plugin will draw gears in Inkscape ( a free OS vector drawing program).
This might help you to match the gear you have by direct comparison with a 2D drawing.
You can also export to openSCAD directly but this will only make simple gears with no 3D profiling but you can use it to learn about these parameters and make direct 2D comparisons. Then create gears that match in Greg's library.
Cheers, Mark...
On 12/23/2018 2:14 AM, Kevin Toppenberg wrote:
I am trying to model a gear for an Atlas metal lathe. I have some original (real-life) gears, but want to print one with a different number of teeth.
I have found this gear library by GregFrost: https://www.thingiverse.com/thing:3575/files
I know that this list is not responsible for the library, but it seems to be a good one, and I am hoping someone here can help.
My question is about the units of the input parameters. For example, in the file parametric_involute_gear_v5.0.scad there are some example gears. I modified one slightly as follows:
gear (number_of_teeth=64,
circular_pitch=285.0,
circles=0);
I chose the value for circular_pitch experimentally. First I put an Echo() statement in the gear_shape module such that it reports the minor diameter, pitch diameter, and major diameter (in mm). I then slowly modified the circular_pitch value until it matched the measurements of my actual real-life gear, taken with my micrometer.
I am confused about what circular_pitch is supposed to represent. I reviewed standard gear terms from here: https://en.wikipedia.org/wiki/List_of_gear_nomenclature#Circular_Pitch
Circular pitch should be the distance (in mm) from tooth to tooth. In my actual real-life gear, the value is about 5 mm.
On a slightly different tact, I am also confused about gear terminology used for my lathe. The gears are typically described using inches and diametral pitch (which is supposed to be 1/circular_pitch). According to this site: https://www.practicalmachinist.com/vb/general/need-atlas-lathe-gear-208658/ (which references here: http://www.lathes.co.uk/atlas/), Atlas gears use a 16DP, which I think means 16 diametral pitch or 16 teeth per inch. I'm not sure I believe this number, because my real-life gear with 20 teeth has a diameter of 1.475 inches, circumference of ~4.3 inches, and thus 20/4.3 = ~4.6 teeth/inch.
Summary:
- Can anyone help me understand the units for the circular_pitch parameter in the gear() module as described above?
- Can anyone see the source of my confusion about the 16DP
Thanks in advance,
Kevin T
<pre class="moz-quote-pre" wrap="">_______________________________________________ OpenSCAD mailing list <a class="moz-txt-link-abbreviated" href="mailto:Discuss@lists.openscad.org">Discuss@lists.openscad.org</a> <a class="moz-txt-link-freetext" href="http://lists.openscad.org/mailman/listinfo/discuss_lists.openscad.org">http://lists.openscad.org/mailman/listinfo/discuss_lists.openscad.org</a>
Kevin,
having programmed, designed and printed a lot of gears and gear types, the
last I would recommend you is to use a 3D-printed gear in a metal lathe.
Even if you have a SLM printer at hand, the result won't be usable on the
long run in a production machine. You risk a lot when putting a minor
quality gear into such a device.
Gears used in lathes are usually of standard pitch und can be bought from
the manufacturer even for old machines. Did you do an Ebay search?
But to answer your question and to complete your information about gears. DP
is a kind of a crook to be able to measure gears somehow in inch. Using it
is somehow magic and not very intuitive.
The metric system is more clear. You have a modulus m and a number z of
theeth. With this your pitch diameter d=mz. The outer diameter of a gear is
usually od=d+addendum, with addendum < 2m.
So, starting with addendum = 2*m, od=1.475 inches = 37.47 mm and z=20 will
give you a modulus of 1.70xx, which is uncommon. A common module is m=1.75.
Why? because you can buy cutting tools for this module, and many lathes use
it. This will result in a pitch diameter of 35mm or 1.378 inch. Further you
must know the pressure angle w, which you can't measure. 20° is normal, but
there are other systems. Maybe it its 14.5°, as was mentioned before. And
last but not least many gears have a profile shift to further adapt the
pitch diameter.
If you want to check all this with your given gear set, you can see my post:
https://www.thingiverse.com/thing:636119 and download my library gears.scad.
It will prompt you the pitch and the outer diameter and some other useful
information to the console. However it uses millimeters. It also provides a
help function. This is your gear:
use<gears.scad>
help(); // see what the lib contains and the prototypes of the modules
gear(m=1.75, z=20, w=14.5);
and your new gear will simply be:
gear(m=1.75, z=64, w=14.5);
--
Sent from: http://forum.openscad.org/
Nop head,
Thank you for your reply. The reason I was talking about circumference is
because I was calculating the actual number of teeth per inch on my actual
gear. To calculate that, I had to know the distance along the surface to
divide the 20 teeth between. That involves the circumference.
I'll keep my eyes out for a bug in the library.
Thanks.
On Sat, Dec 22, 2018 at 8:53 AM nop head nop.head@gmail.com wrote:
I am not familiar with Greg's library but DP is not about circumference.
It is the number of teeth per inch of its pitch diameter, an odd measure
that doesn't really have a physical meaning because the teeth go around the
circumference, not across the diameter.
Also the pitch diameter is not the outside diameter, it is the diameter
where the teeth mesh, sort of half way down the tooth. So you can mesh two
gears if they have the same DP and you space them apart by half the sum of
the pitch diameters.
I have a vague memory that Greg's library has a bug in the way
circular_pitch is used.
On Sat, 22 Dec 2018 at 13:16, Kevin Toppenberg kdtop3@gmail.com wrote:
I am trying to model a gear for an Atlas metal lathe. I have some
original (real-life) gears, but want to print one with a different number
of teeth.
I have found this gear library by GregFrost:
https://www.thingiverse.com/thing:3575/files
I know that this list is not responsible for the library, but it seems to
be a good one, and I am hoping someone here can help.
My question is about the units of the input parameters. For example, in
the file parametric_involute_gear_v5.0.scad there are some example gears.
I modified one slightly as follows:
gear (number_of_teeth=64,
circular_pitch=285.0,
circles=0);
I chose the value for circular_pitch experimentally. First I put an
Echo() statement in the gear_shape module such that it reports the minor
diameter, pitch diameter, and major diameter (in mm). I then slowly
modified the circular_pitch value until it matched the measurements of my
actual real-life gear, taken with my micrometer.
I am confused about what circular_pitch is supposed to represent. I
reviewed standard gear terms from here:
https://en.wikipedia.org/wiki/List_of_gear_nomenclature#Circular_Pitch
Circular pitch should be the distance (in mm) from tooth to tooth. In my
actual real-life gear, the value is about 5 mm.
On a slightly different tact, I am also confused about gear terminology
used for my lathe. The gears are typically described using inches and
diametral pitch (which is supposed to be 1/circular_pitch). According to
this site:
https://www.practicalmachinist.com/vb/general/need-atlas-lathe-gear-208658/
(which references here: http://www.lathes.co.uk/atlas/), Atlas gears use
a 16DP, which I think means 16 diametral pitch or 16 teeth per inch. I'm
not sure I believe this number, because my real-life gear with 20 teeth has
a diameter of 1.475 inches, circumference of ~4.3 inches, and thus 20/4.3 =
~4.6 teeth/inch.
Summary:
1. Can anyone help me understand the units for the circular_pitch
parameter in the gear() module as described above?
2. Can anyone see the source of my confusion about the 16DP
Thanks in advance,
Kevin T
OpenSCAD mailing list
Discuss@lists.openscad.org
http://lists.openscad.org/mailman/listinfo/discuss_lists.openscad.org
Alex,
Yes, I am trying to add a gear into an existing gear train. So I have to
exactly match the pitch of the others.
Thanks!
Kevin
On Sat, Dec 22, 2018 at 9:36 AM Alex Gibson alex@alexgibson.net wrote:
Hi, I’ve used Greg’s excellent library a lot without ever getting into the
fine detail of this – I’m wondering why you actually need to?
My assumption is that you might be trying to change only one gear of a
pair?
If you can change both gears, then you don’t need to worry much about the
pitches – simply specify the distance between shafts and the gear ratio,
and Greg’s library will take care of it all very nicely.
If you’re hoping to keep using one of the gears, you will need to much
more deeply understand the pitches, or if your main motivation is to
understand how Greg’s library is doing its job, please ignore this useless
intervention!
Cheers,
Alex Gibson
admg consulting
edumaker limited
· Project management
· Operations & Process improvement
· 3D Printing
From: Discuss [mailto:discuss-bounces@lists.openscad.org] *On Behalf Of
*nop head
Sent: 22 December 2018 13:52
To: OpenSCAD general discussion
Subject: Re: [OpenSCAD] Question about gear library
I am not familiar with Greg's library but DP is not about circumference.
It is the number of teeth per inch of its pitch diameter, an odd measure
that doesn't really have a physical meaning because the teeth go around the
circumference, not across the diameter.
Also the pitch diameter is not the outside diameter, it is the diameter
where the teeth mesh, sort of half way down the tooth. So you can mesh two
gears if they have the same DP and you space them apart by half the sum of
the pitch diameters.
I have a vague memory that Greg's library has a bug in the way
circular_pitch is used.
On Sat, 22 Dec 2018 at 13:16, Kevin Toppenberg kdtop3@gmail.com wrote:
I am trying to model a gear for an Atlas metal lathe. I have some
original (real-life) gears, but want to print one with a different number
of teeth.
I have found this gear library by GregFrost:
https://www.thingiverse.com/thing:3575/files
I know that this list is not responsible for the library, but it seems to
be a good one, and I am hoping someone here can help.
My question is about the units of the input parameters. For example, in
the file parametric_involute_gear_v5.0.scad there are some example gears.
I modified one slightly as follows:
gear (number_of_teeth=64,
circular_pitch=285.0,
circles=0);
I chose the value for circular_pitch experimentally. First I put an
Echo() statement in the gear_shape module such that it reports the minor
diameter, pitch diameter, and major diameter (in mm). I then slowly
modified the circular_pitch value until it matched the measurements of my
actual real-life gear, taken with my micrometer.
I am confused about what circular_pitch is supposed to represent. I
reviewed standard gear terms from here:
https://en.wikipedia.org/wiki/List_of_gear_nomenclature#Circular_Pitch
Circular pitch should be the distance (in mm) from tooth to tooth. In my
actual real-life gear, the value is about 5 mm.
On a slightly different tact, I am also confused about gear terminology
used for my lathe. The gears are typically described using inches and
diametral pitch (which is supposed to be 1/circular_pitch). According to
this site:
https://www.practicalmachinist.com/vb/general/need-atlas-lathe-gear-208658/
(which references here: http://www.lathes.co.uk/atlas/), Atlas gears use
a 16DP, which I think means 16 diametral pitch or 16 teeth per inch. I'm
not sure I believe this number, because my real-life gear with 20 teeth has
a diameter of 1.475 inches, circumference of ~4.3 inches, and thus 20/4.3 =
~4.6 teeth/inch.
Summary:
1. Can anyone help me understand the units for the circular_pitch
parameter in the gear() module as described above?
2. Can anyone see the source of my confusion about the 16DP
Thanks in advance,
Kevin T
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
Hugo,
Thank you for this helpful reply. See comments below
On Sat, Dec 22, 2018 at 10:52 AM Hugo Jackson hugo@apres.net wrote:
If you know the diametral pitch of a gear train you should be in pretty
good shape as you can work backwards to determining the pitch diameter and
other necessary dimensions.
As others have noted, diametral pitch is the distance between gear teeth,
I think your definition is not quite right. The units for diametral pitch
are teeth/distance, not distance/tooth. But I get what you mean.
but this is not measured at the outer diameter of the gear but at a
calculated point between the outer diameter of the gear teeth and the
diameter of the base of the teeth, and this is know as the pitch circle or
reference diameter.
pitchDiameter = numberOfTeeth / diametralPitch;
This formula helped me quite a bit. I think I might have been conflating
the two different terms: diametral pitch and pitch diameter. But I see now
that they are clearly different.
So if you want to calculate the pitch diameter for Greg’s routines you can
just count the teeth on the gear you are trying to copy and plug that into
the formula above. If Atlas gears do have a diametral pitch of 16 and you
count the number of teeth accurately :) then you’re gonna end up with a
gear the correct size.
So this worked:
pitch_diameter (inches) = 20 teeth / 16 teeth/inch = 1.25 inches <---
matches my actual gear.
So the gear() module accepts either circular_pitch OR diametral_pitch as
inputs. In a bit of a gotcha, however, the units for the diametral_pitch
module have to be in mm, not inches -- even though diametral pitch is
typically only makes sense in inches. E.g. 16 teeth/inch makes sense to
talk about. The equivalent value, 0.63 teeth/mm seems crazy.
So I mentioned before that I carefully adjusted the circular_pitch until I
got values that matched my real gear. Well, I then made another gear
using the diametral_pitch, and they exactly matched. Hurrah!
I STILL would like to know the units for the circular_pitch Greg is using.
Wikipedia (
https://en.wikipedia.org/wiki/List_of_gear_nomenclature#Circular_Pitch)
says circular pitch is the inverse of diametral_pitch, e.g.
circular_pitch = 1/ diametral_pitch.
But in the gear() module, this conversion is made
circular_pitch = 180/diametral_pitch. <--- what's that 180??
If you want to check that against what you’ve measured as the outside
diameter of your gear you can do the following, noting that the dimension
between the pitchDiameter and the outside diameter is called the addendum
addendum = 1 / diametralPitch;
outsideDiameter = pitchDiameter + (2 * addendum);
Looking at the link you posted (
https://www.practicalmachinist.com/vb/general/need-atlas-lathe-gear-208658/ )
it mentions that atlas gears use a 14.5 degree pressure angle so in
addition to the routine in Greg’s library you’re already calling you’ll
want to include the pressure_angle parameter as well, as the default of 20
is not what you want., e.g.
gear (number_of_teeth=64,
// circular_pitch=285.0, // call greg’s routine with the diametral
pitch parameter.. not circular pitch
diametral_pitch = 16,
pressure_angle = 14.5,
circles=0);
Hope this is helpful.
This was very helpful. I put in the correct pressure_angle and it now looks
just like my actual gear.
Thanks so much!!
Kevin
On Dec 22, 2018, at 1:52 PM, nop head nop.head@gmail.com wrote:
I am not familiar with Greg's library but DP is not about circumference.
It is the number of teeth per inch of its pitch diameter, an odd measure
that doesn't really have a physical meaning because the teeth go around the
circumference, not across the diameter.
Also the pitch diameter is not the outside diameter, it is the diameter
where the teeth mesh, sort of half way down the tooth. So you can mesh two
gears if they have the same DP and you space them apart by half the sum of
the pitch diameters.
I have a vague memory that Greg's library has a bug in the way
circular_pitch is used.
On Sat, 22 Dec 2018 at 13:16, Kevin Toppenberg kdtop3@gmail.com wrote:
I am trying to model a gear for an Atlas metal lathe. I have some
original (real-life) gears, but want to print one with a different number
of teeth.
I have found this gear library by GregFrost:
https://www.thingiverse.com/thing:3575/files
I know that this list is not responsible for the library, but it seems to
be a good one, and I am hoping someone here can help.
My question is about the units of the input parameters. For example, in
the file parametric_involute_gear_v5.0.scad there are some example gears.
I modified one slightly as follows:
gear (number_of_teeth=64,
circular_pitch=285.0,
circles=0);
I chose the value for circular_pitch experimentally. First I put an
Echo() statement in the gear_shape module such that it reports the minor
diameter, pitch diameter, and major diameter (in mm). I then slowly
modified the circular_pitch value until it matched the measurements of my
actual real-life gear, taken with my micrometer.
I am confused about what circular_pitch is supposed to represent. I
reviewed standard gear terms from here:
https://en.wikipedia.org/wiki/List_of_gear_nomenclature#Circular_Pitch
Circular pitch should be the distance (in mm) from tooth to tooth. In my
actual real-life gear, the value is about 5 mm.
On a slightly different tact, I am also confused about gear terminology
used for my lathe. The gears are typically described using inches and
diametral pitch (which is supposed to be 1/circular_pitch). According to
this site:
https://www.practicalmachinist.com/vb/general/need-atlas-lathe-gear-208658/
(which references here: http://www.lathes.co.uk/atlas/), Atlas gears use
a 16DP, which I think means 16 diametral pitch or 16 teeth per inch. I'm
not sure I believe this number, because my real-life gear with 20 teeth has
a diameter of 1.475 inches, circumference of ~4.3 inches, and thus 20/4.3 =
~4.6 teeth/inch.
Summary:
1. Can anyone help me understand the units for the circular_pitch
parameter in the gear() module as described above?
2. Can anyone see the source of my confusion about the 16DP
Thanks in advance,
Kevin T
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Parkinbot,
Thanks for the replay. See comments below.
On Sat, Dec 22, 2018 at 5:44 PM Parkinbot rudolf@digitaldocument.de wrote:
Kevin,
having programmed, designed and printed a lot of gears and gear types, the
last I would recommend you is to use a 3D-printed gear in a metal lathe.
Even if you have a SLM printer at hand, the result won't be usable on the
long run in a production machine. You risk a lot when putting a minor
quality gear into such a device.
Gears used in lathes are usually of standard pitch und can be bought from
the manufacturer even for old machines. Did you do an Ebay search?
There are different types of gears used on metal lathes. You are probably
thinking about gears that are directly connected to the motor and turn the
spindle. That is not what I am doing. Instead, lathes have a secondary
drive rod that moves the carriage along slowly, and these can be plastic.
In fact many of the smaller bench-top lathes use plastic gears for this.
The gears are combined in various combinations to get the drive gear to
move at different speeds compared to the spindle, and this allows creating
threads when making screws etc. These are called "change gears." There
is a great Youtube creator named TubalCain (https://youtu.be/V6Aq0d1070I)
that did a great video on this topic showing that the plastic change gears
work fine. Furthermore, I have printed out a set already (
https://www.thingiverse.com/thing:143893) and they seem to be working OK.
But I just need a size not provided there.
I have looked on Ebay for the gear sets, but they are typically expensive,
i.e. about $150 for a set. Also, I want to make a larger gear than is
usually provided, so that I can slow down my carriage travel even slower.
That gives a better surface finish.
But to answer your question and to complete your information about gears.
DP
is a kind of a crook to be able to measure gears somehow in inch. Using it
is somehow magic and not very intuitive.
The metric system is more clear.
Yes, I agree that the metric system is better. Ten thousand times better.
But I have to work with the information I have. And the gear
specifications for this lathe use the imperial system. :-(
You have a modulus m and a number z of
theeth. With this your pitch diameter d=mz. The outer diameter of a gear
is
usually od=d+addendum, with addendum < 2m.
So, starting with addendum = 2*m, od=1.475 inches = 37.47 mm and z=20 will
give you a modulus of 1.70xx, which is uncommon. A common module is m=1.75.
Why? because you can buy cutting tools for this module, and many lathes use
it. This will result in a pitch diameter of 35mm or 1.378 inch. Further you
must know the pressure angle w, which you can't measure. 20° is normal, but
there are other systems. Maybe it its 14.5°, as was mentioned before. And
last but not least many gears have a profile shift to further adapt the
pitch diameter.
If you want to check all this with your given gear set, you can see my
post:
https://www.thingiverse.com/thing:636119 and download my library
gears.scad.
It will prompt you the pitch and the outer diameter and some other useful
information to the console. However it uses millimeters. It also provides a
help function. This is your gear:
use<gears.scad>
help(); // see what the lib contains and the prototypes of the modules
gear(m=1.75, z=20, w=14.5);
and your new gear will simply be:
gear(m=1.75, z=64, w=14.5);
This library looks great. I'll check it out.
Thanks so much for your help.
Kevin T
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