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
