> On 2 Mar 2022, at 01:37, gene heskett <ghesk...@shentel.net> wrote: > On Tuesday, March 1, 2022 5:56:08 PM EST Peter Hodgson wrote: >> I've offered to make some bronze bearings for a vintage British >> motorbike club. >> >> The bearings have some helical oil grooves on one half of the inner >> diameter. >> >> I thought I could do this with G76 having the pitch twice the length of >> the bush. >> >> G0 X15. Z10. >> G76 P42.0 Z-25. I0.88 J0.3 K1.0 Q29.5 H1 L0 R1.5 >> >> The problem is that the spindle, run via a VFD needs to turn at only 50 >> RPM to be able to have enough velocity on the Z stepper to achieve the >> correct pitch and the spindle doesn't seem to be stable enough or have >> enough torque at those revs to give a cosistent cut. >> >> Does anybody have any ideas how I can check or make the G76 more stable >> at low revs? > That will depend on the resolution of the spindles encoder, however the Z > will follow the encoder fairly accuratly if the resolution is there. I > can set my vfd for 5 hz, which has no feedback from the encoder, and even > if the vfd "slipage" is 50%, g76 follows accuratly enough to cut a > useable thread. My encoder tries to be a quadrature, watching the 60 > tooth bull gear, so it has 240 timing edges per rev. You may hear Z > sputtering and stuttering, but the thread is pretty good. Torque at that > speed may need help, but I limit the current boost the vfd can do the the > FLA listed on the motors nameplate, so low speed heating has never been a > problem. Much of course depends on how you've programmed the vfd, which > AFAIAC, is totally fubared at out of the box settings. The vfd I've found > CAN BE quite compliant to your wishes, thats how I can reverse its > direction while turning 100 revs w/o the backgear, with a 40 lb 8" chuck > mounted, with .25 turn of over shoot after motion issues the reverse > command.
Thanks Gene, Encoder resolution is 500ppr quadrature which Peter confirmed should be good. Not sure why I’m getting the rotational shift in the cut. I’ll check the collet again to make sure there’s no slip. I might have to move over to the mill and try broaching with a synchronised rotary table. Pete > >> Thanks, >> >> Pete >> >> >> >> _______________________________________________ >> 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, 1940) > 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
