It doesn't answer your question but have you considered using thread forming taps? Certainly no gullets to fill!
> -----Original Message----- > From: Gene Heskett [mailto:ghesk...@shentel.net] > Sent: Tuesday, August 01, 2017 4:57 PM > To: Enhanced Machine Controller (EMC) > Subject: [Emc-users] Question on Z backlash vs rigid tapping > > Greetings everybody; > > One of the things I have noted recently was a correlation between the thread > fit, and a commercial bolt screwed into the hole, and I believe it has to do with > my use of a peck routine to do the tapping, more pecks=sloppier fit. > > My spindle doesn't have enough power to drive a 10mm tap in one pass, nor > do I feel comfortable when the gullets of the tap get filled, so I peck at it so I > can clean and add a drop or 2 of buttercutt or rapidtap as I program a 3 to 4 > second pause at the top of the travel to give me time to do that. > > Doing some 8mm holes in 3" pipe walls, I drove it about as hard as the spindle > could manage to keep turning, so I drove it deep enough into the hole per pass > that it only took 6 passes to get the last of the taps taper out of the bottom of > the hole. > > The backlash fly in this soup is the filter I've put in the encoder path to average > the level of the last 4 edges out of the encoder, which works well for that and > allows lots more Pgain to be used. That represents a fixed number of spindle > degrees of lag, which of course causes the rigid tap to not follow the z motion > perfectly. > > I have considered adding additional backlash comp, but the required amount > would change with the tpi, so while that would help, its not a perfect fix since > there is not a way to change it dynamically. > > I could take the filter out, but I'd have to reduce Pgain by at least 75% just to > keep it from hammering the gears in the head from the perceived errors in the > velocity signal caused by a 5% quadrature timing error wobble in a 4 step > repeatable sequence. > > This is not an error the PID's can even see, let alone try to correct. > > Is it time to junk the optical encoder, and install a thin steel gear in its place, > and machine some sliding mounts for at least two of the 3 ats667's so that > finer adjustments to reduce the quadrature noise can be done? I have bent > and otherwise adjusted the opto-interrupters until there is no further > improvements to be had. > > In which case, where might I be able to source a 30-60 tooth gear that is > precisely enough made, is not more than 2.25" in diameter, and only 1/16" > thick? > > The current optical setup gives me 268 edges per rev. 67 slots in the disk. > Mechanical errors in carving the disk would be reduced percentagewise by > applying the error to fewer slots, but that seems counter-productive for rigid > tapping. > > What say you folks? > > Thanks all. > > 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) > Genes Web page <http://geneslinuxbox.net:6309/gene> > > ---------------------------------------------------------------------------- -- > Check out the vibrant tech community on one of the world's most engaging > tech sites, Slashdot.org! http://sdm.link/slashdot > _______________________________________________ > Emc-users mailing list > Emc-users@lists.sourceforge.net > https://lists.sourceforge.net/lists/listinfo/emc-users ------------------------------------------------------------------------------ Check out the vibrant tech community on one of the world's most engaging tech sites, Slashdot.org! http://sdm.link/slashdot _______________________________________________ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
