Re: [Emc-users] Harmonic Drive

[John Dammeyer]

> From: John Dammeyer [mailto:jo...@autoartisans.com]
> 
> I'm headed in the other direction since I'd like LCNC to make it.  First I 
> have to reprint the ring gear though.  Would be much smarter
> to actually make it with 142 teeth instead of 140.  I'll try a different 
> filament.  That will likely also make a difference and maybe
> prevent the stringing.
> 
 
So two more tries, one with the correct 142 teeth and still badly mangled.  
Tried some other slicer parameters and still bad teeth and strings.
 
So on a "why not try" moment I switched from Slic3r to CURA.  Not sure I have 
all the parameters the same but wow!  Nice gear with 0.5module teeth.  
 
And now I have a new problem.  The math for the various harmonic drives (3D 
printed)  as shown in the attached Calculations.jpg.
(140-142)/140=-0.014 or essentially 1/70th the speed of the input in the 
opposite direction.  That makes sense since I just doubled the tooth counts 
from this web page.
https://howtomechatronics.com/how-it-works/what-is-strain-wave-gear-harmonic-drive-a-perfect-gear-set-for-robotics-applications/
 
However the cup with 140T doesn't fit into the ring with 142T and the author 
doesn't really talk about that issue since he used 1.25 module teeth.  
 
The cup has to flex enough to so the narrow part of the formed ellipse is 
narrower than the fixed diameter of the outside ring gear so the teeth clear.  
With 0.5module and 140T the diameter even at rest is almost identical to the 
diameter of the 142T gear.  Elongating it to be elliptical so that the two long 
ends can mesh with the slightly larger count gear isn't physically possible.
 
I made up a spreadsheet to make it easier to play with values.  Given my cup 
gear of 140T module 0.5 I would need a ring gear of 147 teeth to get an even 
20:1 and the cup would flex just enough to clear the teeth.
 
I'll post the results.  Not sure what the tooth count or module is on my Brand 
Harmonic Drive.  Quite possible they've chosen both a specific module and tooth 
count to get exactly 50:1 or 100:1. 
 
Playing with my spreadsheet I get the following (although I'm still using 
0.5module tooth size here):
Module 0.3
Tooth count on cup 400
Diameter of cup 120.6mm  (not small)
Ring Gear 408
Ratio 50:1
 
John
 
 
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Re: [Emc-users] Harmonic Drive

[John Dammeyer]

I installed Gene's CAD program and exported as STL because FreeCAD didn't 
recognize the format.  Or I did something wrong.  The generated STL file 
wouldn't export as a STEP file in either FreeCAD nor Fusion360.

John

> -Original Message-
> From: Chris Albertson [mailto:albertson.ch...@gmail.com]
> Sent: December-20-21 10:29 PM
> To: Enhanced Machine Controller (EMC)
> Subject: Re: [Emc-users] Harmonic Drive
> 
> On Mon, Dec 20, 2021 at 5:35 PM gene heskett  wrote:
> 
> > On Monday, December 20, 2021 7:03:21 PM EST John Dammeyer wrote:
> > > Perhaps save it as a step file or iges.  I can't read that scad file.
> >
> 
> > I don't think it can output those non-free formats.
> >
> 
> STEP is an ISO standard and
> IGES is a U.S. National Bureau of Standards format.
> 
> Of the two, STEP is more widely universal as "everyone" can read STEP files.
> 
> Also, as said, FreeCAD can import and run SCAD and then can do things like
> add fillets and report or even, generate code for milling.
> 
> I think SCAD is great for making parts that can be algorithmically
> defined.   But I'd
> hate to have to make an organic shape like a automotive body or a power
> tool.
> o it's good to be able to move designs between tools.   STEP is the best
> for that.
> 
> Chris Albertson
> Redondo Beach, California
> 
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Re: [Emc-users] Harmonic Drive

[Chris Albertson]

On Mon, Dec 20, 2021 at 5:35 PM gene heskett  wrote:

> On Monday, December 20, 2021 7:03:21 PM EST John Dammeyer wrote:
> > Perhaps save it as a step file or iges.  I can't read that scad file.
>

> I don't think it can output those non-free formats.
>

STEP is an ISO standard and
IGES is a U.S. National Bureau of Standards format.

Of the two, STEP is more widely universal as "everyone" can read STEP files.

Also, as said, FreeCAD can import and run SCAD and then can do things like
add fillets and report or even, generate code for milling.

I think SCAD is great for making parts that can be algorithmically
defined.   But I'd
hate to have to make an organic shape like a automotive body or a power
tool.
o it's good to be able to move designs between tools.   STEP is the best
for that.

Chris Albertson
Redondo Beach, California

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Re: [Emc-users] Harmonic Drive

[Ralph Stirling]

FreeCAD can input OpenSCAD files and then export
step or iges files.  Before I got more comfortable with
FreeCAD, I would design my part in OpenSCAD, read
the scad file into FreeCAD and then apply fillets before
exporting.  Fillets have historically been a real pain in
OpenSCAD (not sure if they have new methods).

-- Ralph

From: gene heskett [ghesk...@shentel.net]
Sent: Monday, December 20, 2021 5:32 PM
To: Enhanced Machine Controller (EMC)
Subject: Re: [Emc-users] Harmonic Drive


On Monday, December 20, 2021 7:03:21 PM EST John Dammeyer wrote:
> Perhaps save it as a step file or iges.  I can't read that scad file.

I don't think it can output those non-free formats.

OpenSCAD exports an .stl, ready for cura.. And if you go clear to the bottom
of the downloads page the December release is available as an AppImage which
doesn't need anything else to run except in this case, the latest glibc. There
are earlier versions in case your install is buster or older. Runs on mac's
and winderz too. I don't think there's anything in my code that won't run on
the earlier January 2021 AppImage though. OpenSCAD is under steady
development, getting faster and better with each new release. The .scad file
is pure text, editable in any editor worth calling an editor. That leaves
gedit out, but geany works well as does its own editor.


> > -Original Message-
> > From: gene heskett [mailto:ghesk...@shentel.net]
> > Sent: December-20-21 3:10 PM
> > To: Enhanced Machine Controller (EMC)
> > Subject: Re: [Emc-users] Harmonic Drive
> >
> > On Monday, December 20, 2021 1:49:18 PM EST Chris Albertson wrote:
> > > Yes, he used maybe 30 pounds of metal parts.   And I only saw a few
> > > degrees
> > > of rotation in the video, run it for 100 hours and see what happens.
> > > Flex
> > > is what kills the plastic so after 100 hours it will have had a few
> > > million
> > > cycles.   But still it is 99% made of metal.
> > >
> > > I want to see a 100% plastic unit stand up to 100 hours of use.  It can
> > > be
> > > done but not if the plastic parts flex.
> >
> > Yes it can be done, the drive I posted the openscad file for last week,
> > made out of petg, has been sitting on my kitchen counter, running at 400
> > to 600 rpms input, since the middle of September.  How many hours is that
> > assuming a 24 hr day?
> >
> > > On Mon, Dec 20, 2021 at 10:39 AM Sam Sokolik  wrote:
> > > > Did you watch this video til the end?  I time stamped it.
> > > >
> > > > https://nam12.safelinks.protection.outlook.com/?url=https%3A%2F%2Fyoutu.be%2FeW1GGI55Epc%3Ft%3D878data=04%7C01%7Cralph.stirling%40wallawalla.edu%7Cc48b8062a70346cc9c6e08d9c421c8eb%7Cd958f048e43142779c8debfb75e7aa64%7C0%7C1%7C637756471663573305%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C3000sdata=ctfixojKZGmwad6Y00oNXojrOy4V4zok470xvKgpGRY%3Dreserved=0
> > > >
> > > > sam
> > > >
> > > >
> > > >
> > > > On Mon, Dec 20, 2021 at 12:26 PM Chris Albertson <
> > > > albertson.ch...@gmail.com>
> > > >
> > > > wrote:
> > > > > On Fri, Dec 17, 2021 at 6:05 PM Sam Sokolik 
wrote:
> > > > > > Hmm - seems we are making things a bit more complicated than they
> > > > > > need
> > > >
> > > > to
> > > >
> > > > > > be..  Why didn't the simple flex gear work ok?   You need to make
> > > > > > the
> > > > > > system with fine enough splines that the flexure is at a
> > > > > > minimum...
> > > > >
> > > > > You
> > > > >
> > > > > > can lower the backlash to a minimum by applying a small amount of
> > > > > > pressure to the system.
> > > > >
> > > > > The problem with small splines is that he is making this with
> > > > > printed
> > > > > plastic.   There is a minimum feature size that works.  Seriously
> > > > > you
> > > >
> > > > want
> > > >
> > > > > to stay above module 0.5 and bigger if you can.   Mod 1.0 is more
> > > > > realistic  There are two reasons.  (1) plastic is not very strong
> > > > > unless
> > > > > you make the parts big and (2) the printer makes parts with
> > > > > dimensional
> > > > > tolerances of about 0.4 mm so if your parts have 1mm features you
> > > > > can
> > > > > expect 50% dimensional errors.  That said, modulo 1.0 gears work
> > > > > really
> > > > > well.  Smaler ones have a short life.
> > > > >
> > > > > Finally ANY flexing at all is the death of printed parts.  They fail
> > > > > by
> > > >
> > > > the
> > > >
> > > > > failure of interlayer adhesion.  Think of printed plastic like it is
> > > > > soft
> > > > > pine wood.  When making gears from yellow pine, the direction of the
> > > >
> > > > grain
> > > >
> > > > > matters a lot and no one would think of making module 0.5 gears with
> > > >
> > > > pine.
> > > >
> > > > > I've been able to build an entire CNC conversion kit for a mini-mill
> > > > > from
> > > > > printed plastic.  The stuff is VERY rigid and strong if you make the
> > > >
> > > > parts
> > > >
> > > > > large enough
> > > > >
> > > > > 

Re: [Emc-users] Harmonic Drive

[gene heskett]

On Monday, December 20, 2021 7:03:21 PM EST John Dammeyer wrote:
> Perhaps save it as a step file or iges.  I can't read that scad file.
 
I don't think it can output those non-free formats.

OpenSCAD exports an .stl, ready for cura.. And if you go clear to the bottom 
of the downloads page the December release is available as an AppImage which 
doesn't need anything else to run except in this case, the latest glibc. There 
are earlier versions in case your install is buster or older. Runs on mac's 
and winderz too. I don't think there's anything in my code that won't run on 
the earlier January 2021 AppImage though. OpenSCAD is under steady 
development, getting faster and better with each new release. The .scad file 
is pure text, editable in any editor worth calling an editor. That leaves 
gedit out, but geany works well as does its own editor.


> > -Original Message-
> > From: gene heskett [mailto:ghesk...@shentel.net]
> > Sent: December-20-21 3:10 PM
> > To: Enhanced Machine Controller (EMC)
> > Subject: Re: [Emc-users] Harmonic Drive
> > 
> > On Monday, December 20, 2021 1:49:18 PM EST Chris Albertson wrote:
> > > Yes, he used maybe 30 pounds of metal parts.   And I only saw a few
> > > degrees
> > > of rotation in the video, run it for 100 hours and see what happens.  
> > > Flex
> > > is what kills the plastic so after 100 hours it will have had a few
> > > million
> > > cycles.   But still it is 99% made of metal.
> > > 
> > > I want to see a 100% plastic unit stand up to 100 hours of use.  It can
> > > be
> > > done but not if the plastic parts flex.
> > 
> > Yes it can be done, the drive I posted the openscad file for last week,
> > made out of petg, has been sitting on my kitchen counter, running at 400
> > to 600 rpms input, since the middle of September.  How many hours is that
> > assuming a 24 hr day?
> > 
> > > On Mon, Dec 20, 2021 at 10:39 AM Sam Sokolik  wrote:
> > > > Did you watch this video til the end?  I time stamped it.
> > > > 
> > > > https://youtu.be/eW1GGI55Epc?t=878
> > > > 
> > > > sam
> > > > 
> > > > 
> > > > 
> > > > On Mon, Dec 20, 2021 at 12:26 PM Chris Albertson <
> > > > albertson.ch...@gmail.com>
> > > > 
> > > > wrote:
> > > > > On Fri, Dec 17, 2021 at 6:05 PM Sam Sokolik  
wrote:
> > > > > > Hmm - seems we are making things a bit more complicated than they
> > > > > > need
> > > > 
> > > > to
> > > > 
> > > > > > be..  Why didn't the simple flex gear work ok?   You need to make
> > > > > > the
> > > > > > system with fine enough splines that the flexure is at a
> > > > > > minimum...
> > > > > 
> > > > > You
> > > > > 
> > > > > > can lower the backlash to a minimum by applying a small amount of
> > > > > > pressure to the system.
> > > > > 
> > > > > The problem with small splines is that he is making this with
> > > > > printed
> > > > > plastic.   There is a minimum feature size that works.  Seriously
> > > > > you
> > > > 
> > > > want
> > > > 
> > > > > to stay above module 0.5 and bigger if you can.   Mod 1.0 is more
> > > > > realistic  There are two reasons.  (1) plastic is not very strong
> > > > > unless
> > > > > you make the parts big and (2) the printer makes parts with
> > > > > dimensional
> > > > > tolerances of about 0.4 mm so if your parts have 1mm features you
> > > > > can
> > > > > expect 50% dimensional errors.  That said, modulo 1.0 gears work
> > > > > really
> > > > > well.  Smaler ones have a short life.
> > > > > 
> > > > > Finally ANY flexing at all is the death of printed parts.  They fail
> > > > > by
> > > > 
> > > > the
> > > > 
> > > > > failure of interlayer adhesion.  Think of printed plastic like it is
> > > > > soft
> > > > > pine wood.  When making gears from yellow pine, the direction of the
> > > > 
> > > > grain
> > > > 
> > > > > matters a lot and no one would think of making module 0.5 gears with
> > > > 
> > > > pine.
> > > > 
> > > > > I've been able to build an entire CNC conversion kit for a mini-mill
> > > > > from
> > > > > printed plastic.  The stuff is VERY rigid and strong if you make the
> > > > 
> > > > parts
> > > > 
> > > > > large enough
> > > > > 
> > > > > > sam
> > > > > > 
> > > > > > On Fri, Dec 17, 2021 at 7:46 PM John Dammeyer
> > > > > > 
> > > > > > 
> > > > > > wrote:
> > > > > > > Alright.  So it spins really freely but keeping the planetary
> > > > > > > cluster
> > > > > > > centred is a bit of an issue.  So the attached photo shows
> > > > > > > roughly
> > > > > 
> > > > > (very
> > > > > 
> > > > > > > roughly) what I had in mind.
> > > > > > > 
> > > > > > > With the right coupler between the motor and the gear cluster
> > > > > > > the
> > > > > > > planetary assembly should stay in the same place.  There really
> > > > > > > isn't
> > > > > 
> > > > > any
> > > > > 
> > > > > > > axial load.  There is a place for a 40mmx19mm bearing that I
> > > > > > > happen
> > > > 
> > > > to
> > > > 
> > > > > > have
> > > > > > 
> > > > > > > on hand.
> > > > > > > 
> > > > > > > But what 

Re: [Emc-users] Harmonic Drive

[John Dammeyer]

Perhaps save it as a step file or iges.  I can't read that scad file.

> -Original Message-
> From: gene heskett [mailto:ghesk...@shentel.net]
> Sent: December-20-21 3:10 PM
> To: Enhanced Machine Controller (EMC)
> Subject: Re: [Emc-users] Harmonic Drive
> 
> On Monday, December 20, 2021 1:49:18 PM EST Chris Albertson wrote:
> > Yes, he used maybe 30 pounds of metal parts.   And I only saw a few degrees
> > of rotation in the video, run it for 100 hours and see what happens.   Flex
> > is what kills the plastic so after 100 hours it will have had a few million
> > cycles.   But still it is 99% made of metal.
> >
> > I want to see a 100% plastic unit stand up to 100 hours of use.  It can be
> > done but not if the plastic parts flex.
> >
> Yes it can be done, the drive I posted the openscad file for last week, made
> out of petg, has been sitting on my kitchen counter, running at 400 to 600
> rpms input, since the middle of September.  How many hours is that assuming a
> 24 hr day?
> > On Mon, Dec 20, 2021 at 10:39 AM Sam Sokolik  wrote:
> > > Did you watch this video til the end?  I time stamped it.
> > >
> > > https://youtu.be/eW1GGI55Epc?t=878
> > >
> > > sam
> > >
> > >
> > >
> > > On Mon, Dec 20, 2021 at 12:26 PM Chris Albertson <
> > > albertson.ch...@gmail.com>
> > >
> > > wrote:
> > > > On Fri, Dec 17, 2021 at 6:05 PM Sam Sokolik  wrote:
> > > > > Hmm - seems we are making things a bit more complicated than they need
> > >
> > > to
> > >
> > > > > be..  Why didn't the simple flex gear work ok?   You need to make the
> > > > > system with fine enough splines that the flexure is at a minimum...
> > > >
> > > > You
> > > >
> > > > > can lower the backlash to a minimum by applying a small amount of
> > > > > pressure to the system.
> > > >
> > > > The problem with small splines is that he is making this with printed
> > > > plastic.   There is a minimum feature size that works.  Seriously you
> > >
> > > want
> > >
> > > > to stay above module 0.5 and bigger if you can.   Mod 1.0 is more
> > > > realistic  There are two reasons.  (1) plastic is not very strong unless
> > > > you make the parts big and (2) the printer makes parts with dimensional
> > > > tolerances of about 0.4 mm so if your parts have 1mm features you can
> > > > expect 50% dimensional errors.  That said, modulo 1.0 gears work really
> > > > well.  Smaler ones have a short life.
> > > >
> > > > Finally ANY flexing at all is the death of printed parts.  They fail by
> > >
> > > the
> > >
> > > > failure of interlayer adhesion.  Think of printed plastic like it is
> > > > soft
> > > > pine wood.  When making gears from yellow pine, the direction of the
> > >
> > > grain
> > >
> > > > matters a lot and no one would think of making module 0.5 gears with
> > >
> > > pine.
> > >
> > > > I've been able to build an entire CNC conversion kit for a mini-mill
> > > > from
> > > > printed plastic.  The stuff is VERY rigid and strong if you make the
> > >
> > > parts
> > >
> > > > large enough
> > > >
> > > > > sam
> > > > >
> > > > > On Fri, Dec 17, 2021 at 7:46 PM John Dammeyer 
> > > > >
> > > > > wrote:
> > > > > > Alright.  So it spins really freely but keeping the planetary
> > > > > > cluster
> > > > > > centred is a bit of an issue.  So the attached photo shows roughly
> > > >
> > > > (very
> > > >
> > > > > > roughly) what I had in mind.
> > > > > >
> > > > > > With the right coupler between the motor and the gear cluster the
> > > > > > planetary assembly should stay in the same place.  There really
> > > > > > isn't
> > > >
> > > > any
> > > >
> > > > > > axial load.  There is a place for a 40mmx19mm bearing that I happen
> > >
> > > to
> > >
> > > > > have
> > > > >
> > > > > > on hand.
> > > > > >
> > > > > > But what about the driven ring gear?  In one of the model shops
> > >
> > > today I
> > >
> > > > > > saw a package of 100 5.5mm stainless steel balls they sell for
> > >
> > > putting
> > >
> > > > > into
> > > > >
> > > > > > paint bottles to help mix them up.
> > > > > >
> > > > > > Seemed and ideal size for a bearing race between the two ring gears.
> > > > >
> > > > > Kind
> > > > >
> > > > > > of like what Gene H. stated he did on his setup.  (Pictures?)  So
> > > > > > the
> > > > >
> > > > > Blue
> > > > >
> > > > > > Gear is fixed.  The Green Rotates.  The lazy susan like bearing
> > >
> > > between
> > >
> > > > > > handles axial pressure in the direction of the blue gear.  But
> > > > > > really
> > > >
> > > > the
> > > >
> > > > > > only thing holding up the green ring gear is the planetary assembly.
> > > > > >
> > > > > > Say we wanted to mount a face plate or chuck onto the green gear.
> > >
> > > I'm
> > >
> > > > > > open to ideas on how to stabilize that.  Sketches would be great.
> > > > > >
> > > > > > Methinks a part that surrounds the blue gear and extends over the
> > >
> > > green
> > >
> > > > > > and they also have a bearing race between.  Or we make a similar
> > > >
> > > > bearing
> > > >
> > 

Re: [Emc-users] Harmonic Drive

[gene heskett]

On Monday, December 20, 2021 1:49:18 PM EST Chris Albertson wrote:
> Yes, he used maybe 30 pounds of metal parts.   And I only saw a few degrees
> of rotation in the video, run it for 100 hours and see what happens.   Flex
> is what kills the plastic so after 100 hours it will have had a few million
> cycles.   But still it is 99% made of metal.
> 
> I want to see a 100% plastic unit stand up to 100 hours of use.  It can be
> done but not if the plastic parts flex.
> 
Yes it can be done, the drive I posted the openscad file for last week, made 
out of petg, has been sitting on my kitchen counter, running at 400 to 600 
rpms input, since the middle of September.  How many hours is that assuming a 
24 hr day?
> On Mon, Dec 20, 2021 at 10:39 AM Sam Sokolik  wrote:
> > Did you watch this video til the end?  I time stamped it.
> > 
> > https://youtu.be/eW1GGI55Epc?t=878
> > 
> > sam
> > 
> > 
> > 
> > On Mon, Dec 20, 2021 at 12:26 PM Chris Albertson <
> > albertson.ch...@gmail.com>
> > 
> > wrote:
> > > On Fri, Dec 17, 2021 at 6:05 PM Sam Sokolik  wrote:
> > > > Hmm - seems we are making things a bit more complicated than they need
> > 
> > to
> > 
> > > > be..  Why didn't the simple flex gear work ok?   You need to make the
> > > > system with fine enough splines that the flexure is at a minimum...
> > > 
> > > You
> > > 
> > > > can lower the backlash to a minimum by applying a small amount of
> > > > pressure to the system.
> > > 
> > > The problem with small splines is that he is making this with printed
> > > plastic.   There is a minimum feature size that works.  Seriously you
> > 
> > want
> > 
> > > to stay above module 0.5 and bigger if you can.   Mod 1.0 is more
> > > realistic  There are two reasons.  (1) plastic is not very strong unless
> > > you make the parts big and (2) the printer makes parts with dimensional
> > > tolerances of about 0.4 mm so if your parts have 1mm features you can
> > > expect 50% dimensional errors.  That said, modulo 1.0 gears work really
> > > well.  Smaler ones have a short life.
> > > 
> > > Finally ANY flexing at all is the death of printed parts.  They fail by
> > 
> > the
> > 
> > > failure of interlayer adhesion.  Think of printed plastic like it is
> > > soft
> > > pine wood.  When making gears from yellow pine, the direction of the
> > 
> > grain
> > 
> > > matters a lot and no one would think of making module 0.5 gears with
> > 
> > pine.
> > 
> > > I've been able to build an entire CNC conversion kit for a mini-mill
> > > from
> > > printed plastic.  The stuff is VERY rigid and strong if you make the
> > 
> > parts
> > 
> > > large enough
> > > 
> > > > sam
> > > > 
> > > > On Fri, Dec 17, 2021 at 7:46 PM John Dammeyer 
> > > > 
> > > > wrote:
> > > > > Alright.  So it spins really freely but keeping the planetary
> > > > > cluster
> > > > > centred is a bit of an issue.  So the attached photo shows roughly
> > > 
> > > (very
> > > 
> > > > > roughly) what I had in mind.
> > > > > 
> > > > > With the right coupler between the motor and the gear cluster the
> > > > > planetary assembly should stay in the same place.  There really
> > > > > isn't
> > > 
> > > any
> > > 
> > > > > axial load.  There is a place for a 40mmx19mm bearing that I happen
> > 
> > to
> > 
> > > > have
> > > > 
> > > > > on hand.
> > > > > 
> > > > > But what about the driven ring gear?  In one of the model shops
> > 
> > today I
> > 
> > > > > saw a package of 100 5.5mm stainless steel balls they sell for
> > 
> > putting
> > 
> > > > into
> > > > 
> > > > > paint bottles to help mix them up.
> > > > > 
> > > > > Seemed and ideal size for a bearing race between the two ring gears.
> > > > 
> > > > Kind
> > > > 
> > > > > of like what Gene H. stated he did on his setup.  (Pictures?)  So
> > > > > the
> > > > 
> > > > Blue
> > > > 
> > > > > Gear is fixed.  The Green Rotates.  The lazy susan like bearing
> > 
> > between
> > 
> > > > > handles axial pressure in the direction of the blue gear.  But
> > > > > really
> > > 
> > > the
> > > 
> > > > > only thing holding up the green ring gear is the planetary assembly.
> > > > > 
> > > > > Say we wanted to mount a face plate or chuck onto the green gear.
> > 
> > I'm
> > 
> > > > > open to ideas on how to stabilize that.  Sketches would be great.
> > > > > 
> > > > > Methinks a part that surrounds the blue gear and extends over the
> > 
> > green
> > 
> > > > > and they also have a bearing race between.  Or we make a similar
> > > 
> > > bearing
> > > 
> > > > > mount to the rear one for the front with the gear cluster holding
> > 
> > this
> > 
> > > in
> > > 
> > > > > place extended out to the bearing.  Now the faceplate is attached to
> > > > 
> > > > this.
> > > > 
> > > > > But a lot more axial twist on the small bearing in the middle.
> > > > > 
> > > > > Thanks
> > > > > John
> > > > > 
> > > > > ___
> > > > > Emc-users mailing list
> > > > > Emc-users@lists.sourceforge.net
> > > > > 

Re: [Emc-users] Harmonic Drive

[Chris Albertson]

I got the idea to post process the gears with heat when I was experimenting
with brass inserts.   They make this tool for installing inserts.  One end
is turned to fit the insert the other is turned to exactly fit my
temperature control solder iron.   I set the iron for 180C and the insert
is pretty much exactly at 180C after 5 seconds on the tool.I thought I
could make a brass gear shaft that fits my Hakko solder station.  Even if I
used the gadget as a hand tool I could improve a gear like in your photo.

The Hakko solder iron is fairly powerful it reacts to cooling really fast
and controls the tip temperature well.   But I don't know how large of a
brass gear it could heat

Cover the gear with that ceramic insulation and maybe a big gear.

I covered the bottom side of my 3D printer's build plate with a larger of
ceramic insulation and thin foil tape.  It now heats up in seconds because
it is not radiating heat from the bottom.   This is an easy upgrade.

I'm thinking different from many here because when I want a part I want
dozens of them, not just one.   Each little walking robot has 12 motors and
needs 12 reduction systems and 12 encoders

I bailed on the reduction design as I just can make it small enough and
used R/C hobby servos.   As you can see there is room for improvement.
 But then this leg cost less than $50 complete as shown, drive motors and
all.
https://youtu.be/I93HApHSB0Q

I need at least 8 of these legs.  So I start with this and in the
background try to find a way to use BLDC motors and reduction drives.I
really need some reducers that are about 50mm overall diameter at most and
at least about 50 Kg-cm torque.   I think I'm looking at steel parts.


On Mon, Dec 20, 2021 at 2:15 PM Matthew Herd  wrote:

> So I imagine it is possible to post-process a thermal plastic gear, but at
> that point, maybe it’d be better to set up a gear skiving machine to make
> the flex rings.  If you can get the cutter and angle a rotary axis with
> respect to the spindle, you should be able to do it without much hassle.
> Has anyone considered that route?  Obviously it requires a rotary axis to
> make a rotary axis, but it really doesn’t seem any more insurmountable and
> the results would probably be much more precise.
>
> Matt
>
> > On Dec 20, 2021, at 4:56 PM, Chris Albertson 
> wrote:
> >
> > Is it possible to post process a thermal plastic gear?   Lets say you
> took
> > a high-precision metal gear and heated it to 180C and the rolled it over
> > the printed gear with the correct center to center distance.   You would
> > need to build a test fixture to do this but might be worth it.
> >
> > lately I've been experimenting with brass thread inserts.   I have 1/2
> > dozen different types and printed test blocks with different hole
> diameters
> > and I've tried the soldering iron at different temperatures.   The best
> > results are really good with the M3 size screw failing before the nut.
> > The worst case is they just pull out easily with pliers.
> >
> > The hard part seems to be repeatability and if the hole is parallel or at
> > right angles to the layers. Printer setting and part design seems to
> matter
> > a lot also.I've got a walking-dog type robot and I need to convert it
> > all over to threaded inserts, about 80 places.  I find it helps to think
> if
> > each holes gets larger or smaller then design when it is printed. and
> this
> > depends on ho the hole is connected to the rest of the part.  By walls or
> > sheets or infill..  Engineering is fun...
> >
> >
> >
> > --
> >
> > Chris Albertson
> > Redondo Beach, California
> >
> > ___
> > Emc-users mailing list
> > Emc-users@lists.sourceforge.net
> > https://lists.sourceforge.net/lists/listinfo/emc-users
>
>
>
> ___
> Emc-users mailing list
> Emc-users@lists.sourceforge.net
> https://lists.sourceforge.net/lists/listinfo/emc-users
>


-- 

Chris Albertson
Redondo Beach, California

___
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Re: [Emc-users] Harmonic Drive

[John Dammeyer]

I'm headed in the other direction since I'd like LCNC to make it.  First I have 
to reprint the ring gear though.  Would be much smarter to actually make it 
with 142 teeth instead of 140.  I'll try a different filament.  That will 
likely also make a difference and maybe prevent the stringing. 

And the direction I want to go is with something like this, indexed with my 
STMBL controlled harmonic drive.  Possibly the cutter mounted on the spindle 
quill and the quill running a belt or gears to spin the #8 0.5module cutter 
which is for 135T to Infinity.  The 65mm opening should be more than large 
enough.  

And I still have to design the wave generator bearing assembly.  What I've 
found with the larger 70T cup, printed in PETG with 1mm wall thickness and 
curved bottom is that two wheels don't do a good enough job of molding the cup 
into the ring gear.  Seriously, it's too bendy.  So a 6 bearing setup appears 
to be the best with the sets of 3 as close together as possible.  The other two 
on each side don't even touch the cup and centrifugal force would further move 
the cup away from the side bearings so the extra 4 aren't needed.

John




> -Original Message-
> From: Chris Albertson [mailto:albertson.ch...@gmail.com]
> Sent: December-20-21 1:56 PM
> To: Enhanced Machine Controller (EMC)
> Subject: Re: [Emc-users] Harmonic Drive
> 
> Is it possible to post process a thermal plastic gear?   Lets say you took
> a high-precision metal gear and heated it to 180C and the rolled it over
> the printed gear with the correct center to center distance.   You would
> need to build a test fixture to do this but might be worth it.
> 
> lately I've been experimenting with brass thread inserts.   I have 1/2
> dozen different types and printed test blocks with different hole diameters
> and I've tried the soldering iron at different temperatures.   The best
> results are really good with the M3 size screw failing before the nut.
>  The worst case is they just pull out easily with pliers.
> 
> The hard part seems to be repeatability and if the hole is parallel or at
> right angles to the layers. Printer setting and part design seems to matter
> a lot also.I've got a walking-dog type robot and I need to convert it
> all over to threaded inserts, about 80 places.  I find it helps to think if
> each holes gets larger or smaller then design when it is printed. and this
> depends on ho the hole is connected to the rest of the part.  By walls or
> sheets or infill..  Engineering is fun...
> 
> On Mon, Dec 20, 2021 at 1:05 PM John Dammeyer 
> wrote:
> 
> > As an experiment, now that I've modified the AlibreCAD Python script to
> > use Module or Pitch Diameter and learned how to cut internal spline teeth I
> > created two parts with double the original harmonic drive:  140T and 142T
> > with 0.5module teeth.
> >
> > The cup ID dropped to 65mm from 80mm for the 1.25module 70T.  I've printed
> > it out of PLA again since the yellow I'm using is easier to look at for
> > details compared to the shiny PETG black.
> >
> > Printing the cup went well with clean teeth.  The ring gear is still
> > finishing and I'm not impressed.  For whatever reason it's not looking good.
> >
> > As for profiles, once you go above 135T the standard gear cutter wheels
> > are marked 135 to infinity where infinity means an infinite pitch diameter
> > also known as a rack profile.  So if one wants to use standard gear cutter
> > tooling the number of teeth in the cup/gear assembly must be over 135.
> >
> > To test that theory I recreated the original 70/72T design using AlibreCAD
> > which then generated the involute tooth profile which we've been told isn't
> > as effective as pure triangle or slight sine curve on the tooth slope.
> >
> > Now where before the cup/gear combination would bottom out before making
> > full side contact this one is really tight.  Maybe too tight.  But mix the
> > two with the cup made from the original STEP file profile and the AlibreCAD
> > ring and the fit is perfect.  More testing on that when I find some more
> > 3mm screws of the proper length.
> >
> > Meanwhile once the 3D print of the 0.5 module ring gear is complete I'll
> > see if it's possible to clean up the teeth.  The thing is that the teeth
> > are smaller.  So the cup doesn't have to flex nearly as much as it does
> > with the 1.25module cup.   Perhaps if the 1.25module cup also had 140T and
> > the larger diameter it also wouldn't flex as sharply.   And therefore less
> > chance of cracking.
> >
> > > -Original Message-
> > > From: Chris Albertson [mailto:albertson.ch...@gmail.com]
> > > Sent: December-20-21 10:22 AM
> > > To: Enhanced Machine Controller (EMC)
> > > Subject: Re: [Emc-users] Harmonic Drive
> > >
> > > On Fri, Dec 17, 2021 at 6:05 PM Sam Sokolik  wrote:
> > >
> > > > Hmm - seems we are making things a bit more complicated than they need
> > to
> > > > be..  Why didn't the simple flex gear work ok?   You need to make the

Re: [Emc-users] Harmonic Drive

[John Dammeyer]

There's not a lot of load so manually indexing a rotary table 142 times to cut 
a metal ring gear is tedious but only needs to be done once.  After that with 
the rest in plastic you have the 4th axis.
John


> -Original Message-
> From: Matthew Herd [mailto:herd.m...@gmail.com]
> Sent: December-20-21 2:11 PM
> To: Enhanced Machine Controller (EMC)
> Subject: Re: [Emc-users] Harmonic Drive
> 
> So I imagine it is possible to post-process a thermal plastic gear, but at 
> that point, maybe it�d be better to set up a gear skiving
> machine to make the flex rings.  If you can get the cutter and angle a rotary 
> axis with respect to the spindle, you should be able to do
> it without much hassle.  Has anyone considered that route?  Obviously it 
> requires a rotary axis to make a rotary axis, but it really
> doesn�t seem any more insurmountable and the results would probably be much 
> more precise.
> 
> Matt
> 
> > On Dec 20, 2021, at 4:56 PM, Chris Albertson  
> > wrote:
> >
> > Is it possible to post process a thermal plastic gear?   Lets say you took
> > a high-precision metal gear and heated it to 180C and the rolled it over
> > the printed gear with the correct center to center distance.   You would
> > need to build a test fixture to do this but might be worth it.
> >
> > lately I've been experimenting with brass thread inserts.   I have 1/2
> > dozen different types and printed test blocks with different hole diameters
> > and I've tried the soldering iron at different temperatures.   The best
> > results are really good with the M3 size screw failing before the nut.
> > The worst case is they just pull out easily with pliers.
> >
> > The hard part seems to be repeatability and if the hole is parallel or at
> > right angles to the layers. Printer setting and part design seems to matter
> > a lot also.I've got a walking-dog type robot and I need to convert it
> > all over to threaded inserts, about 80 places.  I find it helps to think if
> > each holes gets larger or smaller then design when it is printed. and this
> > depends on ho the hole is connected to the rest of the part.  By walls or
> > sheets or infill..  Engineering is fun...
> >
> >
> >
> > --
> >
> > Chris Albertson
> > Redondo Beach, California
> >
> > ___
> > Emc-users mailing list
> > Emc-users@lists.sourceforge.net
> > https://lists.sourceforge.net/lists/listinfo/emc-users
> 
> 
> 
> ___
> Emc-users mailing list
> Emc-users@lists.sourceforge.net
> https://lists.sourceforge.net/lists/listinfo/emc-users



___
Emc-users mailing list
Emc-users@lists.sourceforge.net
https://lists.sourceforge.net/lists/listinfo/emc-users

Re: [Emc-users] Harmonic Drive

[Matthew Herd]

So I imagine it is possible to post-process a thermal plastic gear, but at that 
point, maybe it’d be better to set up a gear skiving machine to make the flex 
rings.  If you can get the cutter and angle a rotary axis with respect to the 
spindle, you should be able to do it without much hassle.  Has anyone 
considered that route?  Obviously it requires a rotary axis to make a rotary 
axis, but it really doesn’t seem any more insurmountable and the results would 
probably be much more precise.

Matt

> On Dec 20, 2021, at 4:56 PM, Chris Albertson  
> wrote:
> 
> Is it possible to post process a thermal plastic gear?   Lets say you took
> a high-precision metal gear and heated it to 180C and the rolled it over
> the printed gear with the correct center to center distance.   You would
> need to build a test fixture to do this but might be worth it.
> 
> lately I've been experimenting with brass thread inserts.   I have 1/2
> dozen different types and printed test blocks with different hole diameters
> and I've tried the soldering iron at different temperatures.   The best
> results are really good with the M3 size screw failing before the nut.
> The worst case is they just pull out easily with pliers.
> 
> The hard part seems to be repeatability and if the hole is parallel or at
> right angles to the layers. Printer setting and part design seems to matter
> a lot also.I've got a walking-dog type robot and I need to convert it
> all over to threaded inserts, about 80 places.  I find it helps to think if
> each holes gets larger or smaller then design when it is printed. and this
> depends on ho the hole is connected to the rest of the part.  By walls or
> sheets or infill..  Engineering is fun...
> 
> 
> 
> -- 
> 
> Chris Albertson
> Redondo Beach, California
> 
> ___
> Emc-users mailing list
> Emc-users@lists.sourceforge.net
> https://lists.sourceforge.net/lists/listinfo/emc-users



___
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Emc-users@lists.sourceforge.net
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Re: [Emc-users] Harmonic Drive

[Chris Albertson]

Is it possible to post process a thermal plastic gear?   Lets say you took
a high-precision metal gear and heated it to 180C and the rolled it over
the printed gear with the correct center to center distance.   You would
need to build a test fixture to do this but might be worth it.

lately I've been experimenting with brass thread inserts.   I have 1/2
dozen different types and printed test blocks with different hole diameters
and I've tried the soldering iron at different temperatures.   The best
results are really good with the M3 size screw failing before the nut.
 The worst case is they just pull out easily with pliers.

The hard part seems to be repeatability and if the hole is parallel or at
right angles to the layers. Printer setting and part design seems to matter
a lot also.I've got a walking-dog type robot and I need to convert it
all over to threaded inserts, about 80 places.  I find it helps to think if
each holes gets larger or smaller then design when it is printed. and this
depends on ho the hole is connected to the rest of the part.  By walls or
sheets or infill..  Engineering is fun...

On Mon, Dec 20, 2021 at 1:05 PM John Dammeyer 
wrote:

> As an experiment, now that I've modified the AlibreCAD Python script to
> use Module or Pitch Diameter and learned how to cut internal spline teeth I
> created two parts with double the original harmonic drive:  140T and 142T
> with 0.5module teeth.
>
> The cup ID dropped to 65mm from 80mm for the 1.25module 70T.  I've printed
> it out of PLA again since the yellow I'm using is easier to look at for
> details compared to the shiny PETG black.
>
> Printing the cup went well with clean teeth.  The ring gear is still
> finishing and I'm not impressed.  For whatever reason it's not looking good.
>
> As for profiles, once you go above 135T the standard gear cutter wheels
> are marked 135 to infinity where infinity means an infinite pitch diameter
> also known as a rack profile.  So if one wants to use standard gear cutter
> tooling the number of teeth in the cup/gear assembly must be over 135.
>
> To test that theory I recreated the original 70/72T design using AlibreCAD
> which then generated the involute tooth profile which we've been told isn't
> as effective as pure triangle or slight sine curve on the tooth slope.
>
> Now where before the cup/gear combination would bottom out before making
> full side contact this one is really tight.  Maybe too tight.  But mix the
> two with the cup made from the original STEP file profile and the AlibreCAD
> ring and the fit is perfect.  More testing on that when I find some more
> 3mm screws of the proper length.
>
> Meanwhile once the 3D print of the 0.5 module ring gear is complete I'll
> see if it's possible to clean up the teeth.  The thing is that the teeth
> are smaller.  So the cup doesn't have to flex nearly as much as it does
> with the 1.25module cup.   Perhaps if the 1.25module cup also had 140T and
> the larger diameter it also wouldn't flex as sharply.   And therefore less
> chance of cracking.
>
> > -Original Message-
> > From: Chris Albertson [mailto:albertson.ch...@gmail.com]
> > Sent: December-20-21 10:22 AM
> > To: Enhanced Machine Controller (EMC)
> > Subject: Re: [Emc-users] Harmonic Drive
> >
> > On Fri, Dec 17, 2021 at 6:05 PM Sam Sokolik  wrote:
> >
> > > Hmm - seems we are making things a bit more complicated than they need
> to
> > > be..  Why didn't the simple flex gear work ok?   You need to make the
> > > system with fine enough splines that the flexure is at a minimum...
> You
> > > can lower the backlash to a minimum by applying a small amount of
> > > pressure to the system.
> > >
> >
> > The problem with small splines is that he is making this with printed
> > plastic.   There is a minimum feature size that works.  Seriously you
> want
> > to stay above module 0.5 and bigger if you can.   Mod 1.0 is more
> > realistic  There are two reasons.  (1) plastic is not very strong unless
> > you make the parts big and (2) the printer makes parts with dimensional
> > tolerances of about 0.4 mm so if your parts have 1mm features you can
> > expect 50% dimensional errors.  That said, modulo 1.0 gears work really
> > well.  Smaler ones have a short life.
> >
> > Finally ANY flexing at all is the death of printed parts.  They fail by
> the
> > failure of interlayer adhesion.  Think of printed plastic like it is soft
> > pine wood.  When making gears from yellow pine, the direction of the
> grain
> > matters a lot and no one would think of making module 0.5 gears with
> pine.
> >
> > I've been able to build an entire CNC conversion kit for a mini-mill from
> > printed plastic.  The stuff is VERY rigid and strong if you make the
> parts
> > large enough
> >
> >
> >
> >
> >
> >
> >
> > >
> > > sam
> > >
> > > On Fri, Dec 17, 2021 at 7:46 PM John Dammeyer 
> > > wrote:
> > >
> > > > Alright.  So it spins really freely but keeping the planetary cluster
> > > > centred is a bit of an 

Re: [Emc-users] Harmonic Drive

[Chris Albertson]

On Mon, Dec 20, 2021 at 11:23 AM Andrew  wrote:

>
> > Has anyone tried DLP/SLA printed flex splines?
>

Thinking more along those lines, There are printers that can print metal
parts.
They are expensive but if you only need one or two parts Shapeways can print
them for you.  They offer to print in 316L stainless steel.

There are other even more exotic printers you can buy time on.  SpaceX
prints
the fuel injectors for their rocket engines.   The printer costs literally a
million dollars, but you only need one part made so no need to buy the
printer.





> ___
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> https://lists.sourceforge.net/lists/listinfo/emc-users
>


-- 

Chris Albertson
Redondo Beach, California

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Re: [Emc-users] Harmonic Drive

[John Dammeyer]

I'm going to guess that the +8C ambient temperature in the room that houses the 
printer isn't really helping with the PLA stringing or maybe not able to bond 
to the colder plastic previous layer.  The teeth themselves look reasonable but 
this will take a lot of cleanup.

And of course I have a pretty crappy 3D printer.

John


> -Original Message-
> From: John Dammeyer [mailto:jo...@autoartisans.com]
> Sent: December-20-21 1:01 PM
> To: 'Enhanced Machine Controller (EMC)'
> Subject: Re: [Emc-users] Harmonic Drive
> 
> As an experiment, now that I've modified the AlibreCAD Python script to use 
> Module or Pitch Diameter and learned how to cut
> internal spline teeth I created two parts with double the original harmonic 
> drive:  140T and 142T with 0.5module teeth.
> 
> The cup ID dropped to 65mm from 80mm for the 1.25module 70T.  I've printed it 
> out of PLA again since the yellow I'm using is easier
> to look at for details compared to the shiny PETG black.
> 
> Printing the cup went well with clean teeth.  The ring gear is still 
> finishing and I'm not impressed.  For whatever reason it's not
> looking good.
> 
> As for profiles, once you go above 135T the standard gear cutter wheels are 
> marked 135 to infinity where infinity means an infinite
> pitch diameter also known as a rack profile.  So if one wants to use standard 
> gear cutter tooling the number of teeth in the cup/gear
> assembly must be over 135.
> 
> To test that theory I recreated the original 70/72T design using AlibreCAD 
> which then generated the involute tooth profile which
> we've been told isn't as effective as pure triangle or slight sine curve on 
> the tooth slope.
> 
> Now where before the cup/gear combination would bottom out before making full 
> side contact this one is really tight.  Maybe too
> tight.  But mix the two with the cup made from the original STEP file profile 
> and the AlibreCAD ring and the fit is perfect.  More
> testing on that when I find some more 3mm screws of the proper length.
> 
> Meanwhile once the 3D print of the 0.5 module ring gear is complete I'll see 
> if it's possible to clean up the teeth.  The thing is that the
> teeth are smaller.  So the cup doesn't have to flex nearly as much as it does 
> with the 1.25module cup.   Perhaps if the 1.25module
> cup also had 140T and the larger diameter it also wouldn't flex as sharply.   
> And therefore less chance of cracking.
> 
> > -Original Message-
> > From: Chris Albertson [mailto:albertson.ch...@gmail.com]
> > Sent: December-20-21 10:22 AM
> > To: Enhanced Machine Controller (EMC)
> > Subject: Re: [Emc-users] Harmonic Drive
> >
> > On Fri, Dec 17, 2021 at 6:05 PM Sam Sokolik  wrote:
> >
> > > Hmm - seems we are making things a bit more complicated than they need to
> > > be..  Why didn't the simple flex gear work ok?   You need to make the
> > > system with fine enough splines that the flexure is at a minimum...You
> > > can lower the backlash to a minimum by applying a small amount of
> > > pressure to the system.
> > >
> >
> > The problem with small splines is that he is making this with printed
> > plastic.   There is a minimum feature size that works.  Seriously you want
> > to stay above module 0.5 and bigger if you can.   Mod 1.0 is more
> > realistic  There are two reasons.  (1) plastic is not very strong unless
> > you make the parts big and (2) the printer makes parts with dimensional
> > tolerances of about 0.4 mm so if your parts have 1mm features you can
> > expect 50% dimensional errors.  That said, modulo 1.0 gears work really
> > well.  Smaler ones have a short life.
> >
> > Finally ANY flexing at all is the death of printed parts.  They fail by the
> > failure of interlayer adhesion.  Think of printed plastic like it is soft
> > pine wood.  When making gears from yellow pine, the direction of the grain
> > matters a lot and no one would think of making module 0.5 gears with pine.
> >
> > I've been able to build an entire CNC conversion kit for a mini-mill from
> > printed plastic.  The stuff is VERY rigid and strong if you make the parts
> > large enough
> >
> >
> >
> >
> >
> >
> >
> > >
> > > sam
> > >
> > > On Fri, Dec 17, 2021 at 7:46 PM John Dammeyer 
> > > wrote:
> > >
> > > > Alright.  So it spins really freely but keeping the planetary cluster
> > > > centred is a bit of an issue.  So the attached photo shows roughly (very
> > > > roughly) what I had in mind.
> > > >
> > > > With the right coupler between the motor and the gear cluster the
> > > > planetary assembly should stay in the same place.  There really isn't 
> > > > any
> > > > axial load.  There is a place for a 40mmx19mm bearing that I happen to
> > > have
> > > > on hand.
> > > >
> > > > But what about the driven ring gear?  In one of the model shops today I
> > > > saw a package of 100 5.5mm stainless steel balls they sell for putting
> > > into
> > > > paint bottles to help mix them up.
> > > >
> > > > Seemed and ideal size for a 

Re: [Emc-users] Harmonic Drive

[John Dammeyer]

As an experiment, now that I've modified the AlibreCAD Python script to use 
Module or Pitch Diameter and learned how to cut internal spline teeth I created 
two parts with double the original harmonic drive:  140T and 142T with 
0.5module teeth.  

The cup ID dropped to 65mm from 80mm for the 1.25module 70T.  I've printed it 
out of PLA again since the yellow I'm using is easier to look at for details 
compared to the shiny PETG black. 

Printing the cup went well with clean teeth.  The ring gear is still finishing 
and I'm not impressed.  For whatever reason it's not looking good.

As for profiles, once you go above 135T the standard gear cutter wheels are 
marked 135 to infinity where infinity means an infinite pitch diameter also 
known as a rack profile.  So if one wants to use standard gear cutter tooling 
the number of teeth in the cup/gear assembly must be over 135.

To test that theory I recreated the original 70/72T design using AlibreCAD 
which then generated the involute tooth profile which we've been told isn't as 
effective as pure triangle or slight sine curve on the tooth slope.  

Now where before the cup/gear combination would bottom out before making full 
side contact this one is really tight.  Maybe too tight.  But mix the two with 
the cup made from the original STEP file profile and the AlibreCAD ring and the 
fit is perfect.  More testing on that when I find some more 3mm screws of the 
proper length.

Meanwhile once the 3D print of the 0.5 module ring gear is complete I'll see if 
it's possible to clean up the teeth.  The thing is that the teeth are smaller.  
So the cup doesn't have to flex nearly as much as it does with the 1.25module 
cup.   Perhaps if the 1.25module cup also had 140T and the larger diameter it 
also wouldn't flex as sharply.   And therefore less chance of cracking.

> -Original Message-
> From: Chris Albertson [mailto:albertson.ch...@gmail.com]
> Sent: December-20-21 10:22 AM
> To: Enhanced Machine Controller (EMC)
> Subject: Re: [Emc-users] Harmonic Drive
> 
> On Fri, Dec 17, 2021 at 6:05 PM Sam Sokolik  wrote:
> 
> > Hmm - seems we are making things a bit more complicated than they need to
> > be..  Why didn't the simple flex gear work ok?   You need to make the
> > system with fine enough splines that the flexure is at a minimum...You
> > can lower the backlash to a minimum by applying a small amount of
> > pressure to the system.
> >
> 
> The problem with small splines is that he is making this with printed
> plastic.   There is a minimum feature size that works.  Seriously you want
> to stay above module 0.5 and bigger if you can.   Mod 1.0 is more
> realistic  There are two reasons.  (1) plastic is not very strong unless
> you make the parts big and (2) the printer makes parts with dimensional
> tolerances of about 0.4 mm so if your parts have 1mm features you can
> expect 50% dimensional errors.  That said, modulo 1.0 gears work really
> well.  Smaler ones have a short life.
> 
> Finally ANY flexing at all is the death of printed parts.  They fail by the
> failure of interlayer adhesion.  Think of printed plastic like it is soft
> pine wood.  When making gears from yellow pine, the direction of the grain
> matters a lot and no one would think of making module 0.5 gears with pine.
> 
> I've been able to build an entire CNC conversion kit for a mini-mill from
> printed plastic.  The stuff is VERY rigid and strong if you make the parts
> large enough
> 
> 
> 
> 
> 
> 
> 
> >
> > sam
> >
> > On Fri, Dec 17, 2021 at 7:46 PM John Dammeyer 
> > wrote:
> >
> > > Alright.  So it spins really freely but keeping the planetary cluster
> > > centred is a bit of an issue.  So the attached photo shows roughly (very
> > > roughly) what I had in mind.
> > >
> > > With the right coupler between the motor and the gear cluster the
> > > planetary assembly should stay in the same place.  There really isn't any
> > > axial load.  There is a place for a 40mmx19mm bearing that I happen to
> > have
> > > on hand.
> > >
> > > But what about the driven ring gear?  In one of the model shops today I
> > > saw a package of 100 5.5mm stainless steel balls they sell for putting
> > into
> > > paint bottles to help mix them up.
> > >
> > > Seemed and ideal size for a bearing race between the two ring gears.
> > Kind
> > > of like what Gene H. stated he did on his setup.  (Pictures?)  So the
> > Blue
> > > Gear is fixed.  The Green Rotates.  The lazy susan like bearing between
> > > handles axial pressure in the direction of the blue gear.  But really the
> > > only thing holding up the green ring gear is the planetary assembly.
> > >
> > > Say we wanted to mount a face plate or chuck onto the green gear.  I'm
> > > open to ideas on how to stabilize that.  Sketches would be great.
> > >
> > > Methinks a part that surrounds the blue gear and extends over the green
> > > and they also have a bearing race between.  Or we make a similar bearing
> > > mount to the rear one for 

Re: [Emc-users] Harmonic Drive

[Sam Sokolik]

Yes - because I cannot easily make the harmonic drive out of metal..  Hence
the 3d printed bits.  I have run it for 24 hours at about 700 rpm..   The
gears still look good.  You are engaging a substantial amount of teeth - I
think errors are probably pretty minimal.  I could certainly throw a high
count encoder on it and plot the errors.  (and the normal use case of a 4th
axis isn't full out 100% of the time..)

https://photos.app.goo.gl/MA6tpCP8doLCd9Xn9

sam

On Mon, Dec 20, 2021 at 12:51 PM Chris Albertson 
wrote:

> Yes, he used maybe 30 pounds of metal parts.   And I only saw a few degrees
> of rotation in the video, run it for 100 hours and see what happens.   Flex
> is what kills the plastic so after 100 hours it will have had a few million
> cycles.   But still it is 99% made of metal.
>
> I want to see a 100% plastic unit stand up to 100 hours of use.  It can be
> done but not if the plastic parts flex.
>
> On Mon, Dec 20, 2021 at 10:39 AM Sam Sokolik  wrote:
>
> > Did you watch this video til the end?  I time stamped it.
> >
> > https://youtu.be/eW1GGI55Epc?t=878
> >
> > sam
> >
> >
> >
> > On Mon, Dec 20, 2021 at 12:26 PM Chris Albertson <
> > albertson.ch...@gmail.com>
> > wrote:
> >
> > > On Fri, Dec 17, 2021 at 6:05 PM Sam Sokolik 
> wrote:
> > >
> > > > Hmm - seems we are making things a bit more complicated than they
> need
> > to
> > > > be..  Why didn't the simple flex gear work ok?   You need to make the
> > > > system with fine enough splines that the flexure is at a minimum...
> > > You
> > > > can lower the backlash to a minimum by applying a small amount of
> > > > pressure to the system.
> > > >
> > >
> > > The problem with small splines is that he is making this with printed
> > > plastic.   There is a minimum feature size that works.  Seriously you
> > want
> > > to stay above module 0.5 and bigger if you can.   Mod 1.0 is more
> > > realistic  There are two reasons.  (1) plastic is not very strong
> unless
> > > you make the parts big and (2) the printer makes parts with dimensional
> > > tolerances of about 0.4 mm so if your parts have 1mm features you can
> > > expect 50% dimensional errors.  That said, modulo 1.0 gears work really
> > > well.  Smaler ones have a short life.
> > >
> > > Finally ANY flexing at all is the death of printed parts.  They fail by
> > the
> > > failure of interlayer adhesion.  Think of printed plastic like it is
> soft
> > > pine wood.  When making gears from yellow pine, the direction of the
> > grain
> > > matters a lot and no one would think of making module 0.5 gears with
> > pine.
> > >
> > > I've been able to build an entire CNC conversion kit for a mini-mill
> from
> > > printed plastic.  The stuff is VERY rigid and strong if you make the
> > parts
> > > large enough
> > >
> > >
> > >
> > >
> > >
> > >
> > >
> > > >
> > > > sam
> > > >
> > > > On Fri, Dec 17, 2021 at 7:46 PM John Dammeyer <
> jo...@autoartisans.com>
> > > > wrote:
> > > >
> > > > > Alright.  So it spins really freely but keeping the planetary
> cluster
> > > > > centred is a bit of an issue.  So the attached photo shows roughly
> > > (very
> > > > > roughly) what I had in mind.
> > > > >
> > > > > With the right coupler between the motor and the gear cluster the
> > > > > planetary assembly should stay in the same place.  There really
> isn't
> > > any
> > > > > axial load.  There is a place for a 40mmx19mm bearing that I happen
> > to
> > > > have
> > > > > on hand.
> > > > >
> > > > > But what about the driven ring gear?  In one of the model shops
> > today I
> > > > > saw a package of 100 5.5mm stainless steel balls they sell for
> > putting
> > > > into
> > > > > paint bottles to help mix them up.
> > > > >
> > > > > Seemed and ideal size for a bearing race between the two ring
> gears.
> > > > Kind
> > > > > of like what Gene H. stated he did on his setup.  (Pictures?)  So
> the
> > > > Blue
> > > > > Gear is fixed.  The Green Rotates.  The lazy susan like bearing
> > between
> > > > > handles axial pressure in the direction of the blue gear.  But
> really
> > > the
> > > > > only thing holding up the green ring gear is the planetary
> assembly.
> > > > >
> > > > > Say we wanted to mount a face plate or chuck onto the green gear.
> > I'm
> > > > > open to ideas on how to stabilize that.  Sketches would be great.
> > > > >
> > > > > Methinks a part that surrounds the blue gear and extends over the
> > green
> > > > > and they also have a bearing race between.  Or we make a similar
> > > bearing
> > > > > mount to the rear one for the front with the gear cluster holding
> > this
> > > in
> > > > > place extended out to the bearing.  Now the faceplate is attached
> to
> > > > this.
> > > > > But a lot more axial twist on the small bearing in the middle.
> > > > >
> > > > > Thanks
> > > > > John
> > > > >
> > > > > ___
> > > > > Emc-users mailing list
> > > > > Emc-users@lists.sourceforge.net
> > > > > 

Re: [Emc-users] Harmonic Drive

[Andrew]

пн, 20 груд. 2021 р. о 20:26 Chris Albertson:

> Finally ANY flexing at all is the death of printed parts.  They fail by the
> failure of interlayer adhesion.  Think of printed plastic like it is soft
> pine wood.  When making gears from yellow pine, the direction of the grain
> matters a lot and no one would think of making module 0.5 gears with pine.
>
> Has anyone tried DLP/SLA printed flex splines?

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Re: [Emc-users] Harmonic Drive

[Chris Albertson]

Yes, he used maybe 30 pounds of metal parts.   And I only saw a few degrees
of rotation in the video, run it for 100 hours and see what happens.   Flex
is what kills the plastic so after 100 hours it will have had a few million
cycles.   But still it is 99% made of metal.

I want to see a 100% plastic unit stand up to 100 hours of use.  It can be
done but not if the plastic parts flex.

On Mon, Dec 20, 2021 at 10:39 AM Sam Sokolik  wrote:

> Did you watch this video til the end?  I time stamped it.
>
> https://youtu.be/eW1GGI55Epc?t=878
>
> sam
>
>
>
> On Mon, Dec 20, 2021 at 12:26 PM Chris Albertson <
> albertson.ch...@gmail.com>
> wrote:
>
> > On Fri, Dec 17, 2021 at 6:05 PM Sam Sokolik  wrote:
> >
> > > Hmm - seems we are making things a bit more complicated than they need
> to
> > > be..  Why didn't the simple flex gear work ok?   You need to make the
> > > system with fine enough splines that the flexure is at a minimum...
> > You
> > > can lower the backlash to a minimum by applying a small amount of
> > > pressure to the system.
> > >
> >
> > The problem with small splines is that he is making this with printed
> > plastic.   There is a minimum feature size that works.  Seriously you
> want
> > to stay above module 0.5 and bigger if you can.   Mod 1.0 is more
> > realistic  There are two reasons.  (1) plastic is not very strong unless
> > you make the parts big and (2) the printer makes parts with dimensional
> > tolerances of about 0.4 mm so if your parts have 1mm features you can
> > expect 50% dimensional errors.  That said, modulo 1.0 gears work really
> > well.  Smaler ones have a short life.
> >
> > Finally ANY flexing at all is the death of printed parts.  They fail by
> the
> > failure of interlayer adhesion.  Think of printed plastic like it is soft
> > pine wood.  When making gears from yellow pine, the direction of the
> grain
> > matters a lot and no one would think of making module 0.5 gears with
> pine.
> >
> > I've been able to build an entire CNC conversion kit for a mini-mill from
> > printed plastic.  The stuff is VERY rigid and strong if you make the
> parts
> > large enough
> >
> >
> >
> >
> >
> >
> >
> > >
> > > sam
> > >
> > > On Fri, Dec 17, 2021 at 7:46 PM John Dammeyer 
> > > wrote:
> > >
> > > > Alright.  So it spins really freely but keeping the planetary cluster
> > > > centred is a bit of an issue.  So the attached photo shows roughly
> > (very
> > > > roughly) what I had in mind.
> > > >
> > > > With the right coupler between the motor and the gear cluster the
> > > > planetary assembly should stay in the same place.  There really isn't
> > any
> > > > axial load.  There is a place for a 40mmx19mm bearing that I happen
> to
> > > have
> > > > on hand.
> > > >
> > > > But what about the driven ring gear?  In one of the model shops
> today I
> > > > saw a package of 100 5.5mm stainless steel balls they sell for
> putting
> > > into
> > > > paint bottles to help mix them up.
> > > >
> > > > Seemed and ideal size for a bearing race between the two ring gears.
> > > Kind
> > > > of like what Gene H. stated he did on his setup.  (Pictures?)  So the
> > > Blue
> > > > Gear is fixed.  The Green Rotates.  The lazy susan like bearing
> between
> > > > handles axial pressure in the direction of the blue gear.  But really
> > the
> > > > only thing holding up the green ring gear is the planetary assembly.
> > > >
> > > > Say we wanted to mount a face plate or chuck onto the green gear.
> I'm
> > > > open to ideas on how to stabilize that.  Sketches would be great.
> > > >
> > > > Methinks a part that surrounds the blue gear and extends over the
> green
> > > > and they also have a bearing race between.  Or we make a similar
> > bearing
> > > > mount to the rear one for the front with the gear cluster holding
> this
> > in
> > > > place extended out to the bearing.  Now the faceplate is attached to
> > > this.
> > > > But a lot more axial twist on the small bearing in the middle.
> > > >
> > > > Thanks
> > > > John
> > > >
> > > > ___
> > > > Emc-users mailing list
> > > > Emc-users@lists.sourceforge.net
> > > > https://lists.sourceforge.net/lists/listinfo/emc-users
> > > >
> > >
> > > ___
> > > Emc-users mailing list
> > > Emc-users@lists.sourceforge.net
> > > https://lists.sourceforge.net/lists/listinfo/emc-users
> > >
> >
> >
> > --
> >
> > Chris Albertson
> > Redondo Beach, California
> >
> > ___
> > Emc-users mailing list
> > Emc-users@lists.sourceforge.net
> > https://lists.sourceforge.net/lists/listinfo/emc-users
> >
>
> ___
> Emc-users mailing list
> Emc-users@lists.sourceforge.net
> https://lists.sourceforge.net/lists/listinfo/emc-users
>


-- 

Chris Albertson
Redondo Beach, California

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Re: [Emc-users] Harmonic Drive

[Sam Sokolik]

Did you watch this video til the end?  I time stamped it.

https://youtu.be/eW1GGI55Epc?t=878

sam



On Mon, Dec 20, 2021 at 12:26 PM Chris Albertson 
wrote:

> On Fri, Dec 17, 2021 at 6:05 PM Sam Sokolik  wrote:
>
> > Hmm - seems we are making things a bit more complicated than they need to
> > be..  Why didn't the simple flex gear work ok?   You need to make the
> > system with fine enough splines that the flexure is at a minimum...
> You
> > can lower the backlash to a minimum by applying a small amount of
> > pressure to the system.
> >
>
> The problem with small splines is that he is making this with printed
> plastic.   There is a minimum feature size that works.  Seriously you want
> to stay above module 0.5 and bigger if you can.   Mod 1.0 is more
> realistic  There are two reasons.  (1) plastic is not very strong unless
> you make the parts big and (2) the printer makes parts with dimensional
> tolerances of about 0.4 mm so if your parts have 1mm features you can
> expect 50% dimensional errors.  That said, modulo 1.0 gears work really
> well.  Smaler ones have a short life.
>
> Finally ANY flexing at all is the death of printed parts.  They fail by the
> failure of interlayer adhesion.  Think of printed plastic like it is soft
> pine wood.  When making gears from yellow pine, the direction of the grain
> matters a lot and no one would think of making module 0.5 gears with pine.
>
> I've been able to build an entire CNC conversion kit for a mini-mill from
> printed plastic.  The stuff is VERY rigid and strong if you make the parts
> large enough
>
>
>
>
>
>
>
> >
> > sam
> >
> > On Fri, Dec 17, 2021 at 7:46 PM John Dammeyer 
> > wrote:
> >
> > > Alright.  So it spins really freely but keeping the planetary cluster
> > > centred is a bit of an issue.  So the attached photo shows roughly
> (very
> > > roughly) what I had in mind.
> > >
> > > With the right coupler between the motor and the gear cluster the
> > > planetary assembly should stay in the same place.  There really isn't
> any
> > > axial load.  There is a place for a 40mmx19mm bearing that I happen to
> > have
> > > on hand.
> > >
> > > But what about the driven ring gear?  In one of the model shops today I
> > > saw a package of 100 5.5mm stainless steel balls they sell for putting
> > into
> > > paint bottles to help mix them up.
> > >
> > > Seemed and ideal size for a bearing race between the two ring gears.
> > Kind
> > > of like what Gene H. stated he did on his setup.  (Pictures?)  So the
> > Blue
> > > Gear is fixed.  The Green Rotates.  The lazy susan like bearing between
> > > handles axial pressure in the direction of the blue gear.  But really
> the
> > > only thing holding up the green ring gear is the planetary assembly.
> > >
> > > Say we wanted to mount a face plate or chuck onto the green gear.  I'm
> > > open to ideas on how to stabilize that.  Sketches would be great.
> > >
> > > Methinks a part that surrounds the blue gear and extends over the green
> > > and they also have a bearing race between.  Or we make a similar
> bearing
> > > mount to the rear one for the front with the gear cluster holding this
> in
> > > place extended out to the bearing.  Now the faceplate is attached to
> > this.
> > > But a lot more axial twist on the small bearing in the middle.
> > >
> > > Thanks
> > > John
> > >
> > > ___
> > > Emc-users mailing list
> > > Emc-users@lists.sourceforge.net
> > > https://lists.sourceforge.net/lists/listinfo/emc-users
> > >
> >
> > ___
> > Emc-users mailing list
> > Emc-users@lists.sourceforge.net
> > https://lists.sourceforge.net/lists/listinfo/emc-users
> >
>
>
> --
>
> Chris Albertson
> Redondo Beach, California
>
> ___
> Emc-users mailing list
> Emc-users@lists.sourceforge.net
> https://lists.sourceforge.net/lists/listinfo/emc-users
>

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Re: [Emc-users] Harmonic Drive

[Chris Albertson]

On Fri, Dec 17, 2021 at 6:05 PM Sam Sokolik  wrote:

> Hmm - seems we are making things a bit more complicated than they need to
> be..  Why didn't the simple flex gear work ok?   You need to make the
> system with fine enough splines that the flexure is at a minimum...You
> can lower the backlash to a minimum by applying a small amount of
> pressure to the system.
>

The problem with small splines is that he is making this with printed
plastic.   There is a minimum feature size that works.  Seriously you want
to stay above module 0.5 and bigger if you can.   Mod 1.0 is more
realistic  There are two reasons.  (1) plastic is not very strong unless
you make the parts big and (2) the printer makes parts with dimensional
tolerances of about 0.4 mm so if your parts have 1mm features you can
expect 50% dimensional errors.  That said, modulo 1.0 gears work really
well.  Smaler ones have a short life.

Finally ANY flexing at all is the death of printed parts.  They fail by the
failure of interlayer adhesion.  Think of printed plastic like it is soft
pine wood.  When making gears from yellow pine, the direction of the grain
matters a lot and no one would think of making module 0.5 gears with pine.

I've been able to build an entire CNC conversion kit for a mini-mill from
printed plastic.  The stuff is VERY rigid and strong if you make the parts
large enough







>
> sam
>
> On Fri, Dec 17, 2021 at 7:46 PM John Dammeyer 
> wrote:
>
> > Alright.  So it spins really freely but keeping the planetary cluster
> > centred is a bit of an issue.  So the attached photo shows roughly (very
> > roughly) what I had in mind.
> >
> > With the right coupler between the motor and the gear cluster the
> > planetary assembly should stay in the same place.  There really isn't any
> > axial load.  There is a place for a 40mmx19mm bearing that I happen to
> have
> > on hand.
> >
> > But what about the driven ring gear?  In one of the model shops today I
> > saw a package of 100 5.5mm stainless steel balls they sell for putting
> into
> > paint bottles to help mix them up.
> >
> > Seemed and ideal size for a bearing race between the two ring gears.
> Kind
> > of like what Gene H. stated he did on his setup.  (Pictures?)  So the
> Blue
> > Gear is fixed.  The Green Rotates.  The lazy susan like bearing between
> > handles axial pressure in the direction of the blue gear.  But really the
> > only thing holding up the green ring gear is the planetary assembly.
> >
> > Say we wanted to mount a face plate or chuck onto the green gear.  I'm
> > open to ideas on how to stabilize that.  Sketches would be great.
> >
> > Methinks a part that surrounds the blue gear and extends over the green
> > and they also have a bearing race between.  Or we make a similar bearing
> > mount to the rear one for the front with the gear cluster holding this in
> > place extended out to the bearing.  Now the faceplate is attached to
> this.
> > But a lot more axial twist on the small bearing in the middle.
> >
> > Thanks
> > John
> >
> > ___
> > Emc-users mailing list
> > Emc-users@lists.sourceforge.net
> > https://lists.sourceforge.net/lists/listinfo/emc-users
> >
>
> ___
> Emc-users mailing list
> Emc-users@lists.sourceforge.net
> https://lists.sourceforge.net/lists/listinfo/emc-users
>


-- 

Chris Albertson
Redondo Beach, California

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Re: [Emc-users] Harmonic Drive

[Chris Albertson]

Encoders have gotten very easy and cheap.
These are small enough to fit inside the drive, and only cost $9 on
Amazon.  They are half this price if bought directly from China and even
less if you have custom PCBs made.   This chip on a custom PCB might cost
about $2 (plus about $25 in express DHL shipping)   But Amazon can ship
next day with Prime.I've kind of gotten spoiled with "next day"
shipping.
www.amazon.com/


I'm looking to make a reduction drive too, but I can't use a stepper-driven
harmonic drive.  I need only 1-:1 reduction and the ability to back drive.
 But in either case, these magnetic encoders beat the bulky mechanical ones
and
(1) they are absolute position, not incremental and
(2) they don't need quadrature logic to decode, they output I2C
(3) 12-bits of position resolution
(4) magnetic connection.  So there is no need for a shaft coupler,

The best place to close the position loop is inside the driver, going
through software in a PC introduces performance-killing delay.

On Fri, Dec 17, 2021 at 4:14 PM John Dammeyer 
wrote:

> And now with the 40T and 41T labels on each gear it was possible to spin
> them on the mount so they were all in the same orientation and I then
> constrained one mount hole on each.  Then repositioned the teeth and the
> two rings.  Now they all match back and front.
>
> Have not yet figured out how to set up constraints so the gears turn with
> each other.  Of course the 3D prints take care of that exercise.
>
> Now as an aside would it be more prudent to work an encoder into the green
> output gear for feed back into LCNC or for that matter the motor driver?
> (With the appropriate division ratio).
>
> John
>
>
> > -Original Message-
> > From: John Dammeyer [mailto:jo...@autoartisans.com]
> > Sent: December-17-21 3:43 PM
> > To: 'Enhanced Machine Controller (EMC)'
> > Subject: Re: [Emc-users] Harmonic Drive
> >
> > Here are screen shots of my drawings as imported from the FreeCAD STEP
> files.  The first thing I did to them is add a pattern of 3
> > holes evenly spaced 120 degrees apart.   When I redo these I'll go from
> an equilateral triangle to a form that only allows one way to
> > screw them together.  Then it won't be possible to connect them any way
> but the way a dual extruded version would go together.
> >
> > In my case here, the key hole is on the X axis for both gears so
> connected like that the gear teeth at that position line up too.  Hard to
> > screw that up.
> >
> > More difficult is seeing the positions as you showed in your last
> sketch.   Adding the Teeth number engraved into the gear opposite
> > that tooth allows a user to line up the text horizontally.
> >
> > But change to an isosceles triangle for the hole and identify the gear
> top side with the text and now even without markings it's easy
> > to see which screw should be on the right side with the text line
> parallel on each.
> >
> > Or just create a jig that goes into the bottom of the 40T planet
> arrangement holes.  This would hold the gears in the correct
> > orientation while being inserted into a more complete housing holding
> the ring gears.
> >
> > In either case, the assembly rotates smoothly now.  Just need to make
> something that holds the planetary cluster in frame with the
> > fixed 100T gear.
> >
> > John
> >
> > > -Original Message-
> > > From: Todd Zuercher [mailto:to...@pgrahamdunn.com]
> > > Sent: December-17-21 8:10 AM
> > > To: Enhanced Machine Controller (EMC)
> > > Subject: Re: [Emc-users] Harmonic Drive
> > >
> > > Here is a better image with the clocking points marked on the pinions
> to better illustrate what I mean.
> > >
> > > Andy, I think what you are describing is what I did with my first
> drawing (with four sets of planets).  When the rings have the same
> > > diameter but different tooth counts, you have to fudge the module (and
> probably the tooth profile) of the rings.  (The version of
> > > Freecad I'm using doesn't give me the option to mess with the tooth
> profile.)  With that set up all of the pinions would have the
> > same
> > > tooth counts.  And in the case of a 1 tooth ring count difference, one
> of the planet sets would have no phase shift and could be a
> > > single gear double tall.  But all of the others would have different
> shifts.  For a 3 planet the shift would be +1/3 tooth for one set
> > and
> > > -1/3 for the other set.   This set up has exactly 1 tooth per spider
> rev reduction.
> > >
> > > I dropped the identical ring size version when I discovered that
> making the pinions 1 tooth different made up for the 1tooth
> >