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 <albertson.ch...@gmail.com>
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 <samco...@gmail.com> 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 <samco...@gmail.com>
> 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
> > > > >
> > > > > _______________________________________________
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> > > > > Emc-users@lists.sourceforge.net
> > > > > https://lists.sourceforge.net/lists/listinfo/emc-users
> > > > >
> > > >
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> > > >
> > >
> > >
> > > --
> > >
> > > 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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> >
>
>
> --
>
> Chris Albertson
> Redondo Beach, California
>
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