On Friday 08 May 2020 10:58:57 Gene Heskett wrote: > On Friday 08 May 2020 06:59:44 andy pugh wrote: > > On Fri, 8 May 2020 at 01:23, Gene Heskett <ghesk...@shentel.net> wrote: > > > If the spindle speed is steady, I have heard of folks doing rigid > > > tapping with 1 ppr. Ditto g76. > > > > You can do G76 with 1ppr, but not, sensibly, rigid tapping. > > > > For rigid tapping you need quadrature to detect the moment of > > spindle reversal. There is no reliable way to interpolate that. > > Humm, makes me ask, Andy. I am useing some hal trickery to actually sequence this turnaround and to profile it to where z can follow. Because I am blocking the reversal signal, using it to stop the motor at a controlled decel by a limit3 allowing the encoder time between pulses to detect when it has essentially stopped, then the reversal is allowed thru to the controller, the chosen speed is re-applied to the limit3 and the motor is ramped back up to speed by the output of that limit3. This of course allows a wee bit more overshoot at the bottom of a hole, and if the hole is blind, the possibility of a broken tap. My question is since I've noted looser fitting threads when I am "pecking" a hole thats too big for my spindle to power thru in one stroke, is there a chance of any counts being lost during this turn-around causing a miss-timing to the repeated passes and the tap cutting on the withdrawal?
I normally tap in low gear at less than 300 rpms to cut down on the overshoot. The actual delay is hard to measure, so the only place I've tested is from 3k to 3k the other direction, and it does that in about 400 milliseconds. At 250 revs, its well under a turn of the spindle and looks instant but the human eye is very slow. > > Semi-rigid tapping with a floating holder could be an option with a > > very low count encoder. > > > > I think that 100ppr might be enough for tapping. I wouldn't want to > > go much lower. > > Then choose spindle speeds where the software counter can keep up. > > Andy is correct of course, I was wrong about rigid tapping. > > > Cheers, Gene Heskett 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
