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
