Greetings all; In my rigid tapping, I often peck to final depth due to not having a big enough horse turning the spindle, only about 2. Due to Z slop this often leads to a looser thread fit but is generally usable.
But when tappiing blind holes, there is always the chance of the tap contacting the bottom of the hole and breaking the the tap. This of coarse leads to a long session of EDM to remove the broken tap. At the bottom turn around of each peck I could record the spindle pid's error signal at the instant the reverse comes out of motion, tallying how hard the spindle is working at that instant, with the possibility of detecting, from the error signals increase, when the tap is just touching the debris in the bottom of the hole, and when that condition is reached, add enough to #<_ztmp> to satisfy the while statement driving the peck, terminating the operation before the next peck. This would not save the tap if the turnaround overshoot was large, so slower spindle speeds would be needed, probably under 100 rpms. But at 100 rpms, its much less than 1/4 turn of overshoot on the G0704. I am already instrumented to measure this overshoot, both in z distance and spindle rev fraction. I am even displaying it on the Sheldon, which at 100 revs, can do a turnaround in .25 turn while swinging an 8" 4 jaw chuck that weighs at least 30 lbs. I am not that complete on the G0704, but do record the overshoot in counts of the spindle encoder, at 1460 counts, in a scale of slightly over 7100 per rev. That 20% of a turn. In this case in high gear, probably a bit more in low gear due to the higher motor speed. Does this sound like a worthwhile bit of research? Or just another way to break taps? With most taps shoving some of the cuttings ahead of them, it seems we ought to be able to detect we are crushing the cuttings far enough from the actual contact to save the tap. Finally, for this project, who grinds the best "blind" tap in 5mm x .8 metric? Working in the BS-1's cast iron in this case. Thanks everybody. 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 [email protected] https://lists.sourceforge.net/lists/listinfo/emc-users
