On Friday 28 August 2020 16:04:11 Chris Albertson wrote: > Gene, > > I thought you had the STEP file for this. If you did not download > it, I did and you can have my copy of it here > https://a360.co/2EHlpMr > I do have it, but opening it with the latest freecad, does not get me down into it to modify it.
> I've been reading about printable harmonic drives and the best idea I > found is to use a stainless steel drinking cup as the flex cup (after > cutting off the rim) and gluing a timing belt to the cup to make the > teeth. The steel/rubber composite seems to last a long time. Sounds good, and may work for gear reduction ok, but there would be a huge, high frequency cyclic speed variation due the the shape of the teeth in a timing belt. And that isn't exactly friendly to guiding a star gazers telescope. These won't be that great either, but why design in a known flaw? > On Fri, Aug 28, 2020 at 11:37 AM Gene Heskett <ghesk...@shentel.net> wrote: > > On Friday 28 August 2020 12:36:07 Todd Zuercher wrote: > > > If you think about it the metal toothed cups used in harmonic > > > drives, have to flex in a rather nasty way (it is a little more > > > than just squeezing the mouth into an oval). I'm surprised they > > > last as long as they do. I'm not surprised you are having cracking > > > problems with the pla. What is the distance from where the cup is > > > pinched by the bearing to the face of the cup? Increasing that > > > distance should improve the durability. Also I think I would > > > slightly increase the thickness and add a slight fillet to the > > > inside transitioning from the wall to the cup face. Then taper > > > the cup wall down and have it be it's thinnest (probably thinner > > > than you have it now) for the majority of the height of the cup > > > then thicken it again to accommodate the toothed surface at the > > > bottom. > > > > I don't have the original src, just the stl's that the slicer can > > make g-code out of. So the limits of my ability to adjust such is > > limited to the xyz scale settings of the printer. > > > > > I do have the remains of a busted commercially made harmonic drive > > > in a box on a shelf. It was in the tool changer of a used machine > > > we bought. I don't know how it was originally broken, but it to > > > failed at the transition of wall to face, the previous owner had > > > tried to fix it by welding the cup back together. It worked for > > > about 6 months after we bought the machine, until the welds > > > fatigued and failed. In the mean time the part was redesigned by > > > the harmonic drive manufacturer with a much taller cup for the > > > replacement part (also requiring us to replace of a number of > > > other parts in our tool changer to accommodate the redesigned > > > part.) > > > > I fail to grok the reason they used a expensive part like a harmonic > > drive for speed reduction in a tool changer. Boggles what little > > mind I have left at my years. An eletric wiper motor can be made to > > do that job with adequate accuracy. Really precise location can be > > had by backing up aganst a pawl. Abuse the motor to get the power to > > move a long chain if needed, its not something that has to run 500+ > > miles non-stop in a blizzard. It doesn't run long enough to get hot > > at any one time unless the designer is an idiot. Oh, wait, I've met > > some of them. Some are. > > > > Stay safe and well Todd. > > > > > Todd Zuercher > > > P. Graham Dunn Inc. > > > 630 Henry Street > > > Dalton, Ohio 44618 > > > Phone: (330)828-2105ext. 2031 > > > > > > -----Original Message----- > > > From: Gene Heskett <ghesk...@shentel.net> > > > Sent: Friday, August 28, 2020 11:10 AM > > > To: emc-users@lists.sourceforge.net > > > Subject: SPAM: Re: [Emc-users] precisiomn indexer > > > > > > [EXTERNAL EMAIL] Be sure links are safe. > > > > > > On Friday 28 August 2020 06:18:32 Thomas J Powderly wrote: > > > > Gene an old client called about using a Newbould indexer on his > > > > machine. > > > > > > > > I remember it was a hirth 'gear' or coupler > > > > > > > > Very accurate stacking 'gears' , a way to set a part at precise > > > > angles > > > > > > > > I thought... "Hey Gene could _print_ one" > > > > > > > > as if you dont have enough to do :-) > > > > > > > > just FYI > > > > > > > > TomP > > > > > > > > https://en.wikipedia.org/wiki/Hirth_joint > > > > > > > > https://www.youtube.com/watch?v=3EGGuR5YziE > > > > > > The odd tooth version could probably be done in sub-degree jumps > > > but not with a 3d printers tolerances. > > > > > > I'm learning how to make flexgears for a harmonic drive out of > > > TPU. PLA hasn't enough flex and breaks in less than 5 minutes > > > running time. > > > > > > And I've two that have now run at an output speed of about 1 rev > > > in 4 seconds for over 24 hours. Unlike the really preciely made > > > metal one's, it has to have a touch of backlash, but with a decent > > > driver, and none of the TB series fit that description, because > > > they don't auto-throttle the currants, it looks like I'll have > > > enough torque from a nema 17 motor to drive the worm of a clone > > > BS-1, under cutting load no less. > > > > > > TPU can be a cast iron bitch, its 100x more finicky about temps > > > and speeds than PLA. Currently seems to be working, but at a > > > nozzle temp 15C above whats noted on the no-name box I bought 2 of > > > for a $70 bill. Virtually zero extruder drive grip allowed in a > > > Micro-Swiss hot end that moves the extruder motor to the X > > > carriage. > > > > > > Thanks TomP, stay safe and well, both of you. > > > > > > Cheers, Gene Heskett > > > -- > > > "There are four boxes to be used in defense of liberty: > > > soap, ballot, jury, and ammo. Please use in that order." > > > -Ed Howdershelt (Author) > > > If we desire respect for the law, we must first make the law > > > respectable. - Louis D. Brandeis > > > Genes Web page <http://geneslinuxbox.net:6309/gene> > > > > > > > > > _______________________________________________ > > > 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 > > > > Cheers, Gene Heskett > > -- > > "There are four boxes to be used in defense of liberty: > > soap, ballot, jury, and ammo. Please use in that order." > > -Ed Howdershelt (Author) > > If we desire respect for the law, we must first make the law > > respectable. - Louis D. Brandeis > > Genes Web page <http://geneslinuxbox.net:6309/gene> > > > > > > _______________________________________________ > > Emc-users mailing list > > Emc-users@lists.sourceforge.net > > https://lists.sourceforge.net/lists/listinfo/emc-users Cheers, Gene Heskett -- "There are four boxes to be used in defense of liberty: soap, ballot, jury, and ammo. Please use in that order." -Ed Howdershelt (Author) If we desire respect for the law, we must first make the law respectable. - Louis D. Brandeis Genes Web page <http://geneslinuxbox.net:6309/gene> _______________________________________________ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
