On Friday 16 April 2021 21:33:33 Jon Elson wrote: > On 04/16/2021 12:30 PM, Gene Heskett wrote: > > Greetings all; > > > > I am still looking for a little help in rigid tapping. > > > > Since the GO704 can only muster around 2 hp in its current drive > > configuration, its often that I have to write a peck routine where > > each peck goes just a fraction of a turn farther until the tap is > > deep enough. But something is displacing it vertically just enough > > to make noticeably sloppy fitting threads. > > Yes, I can see how it could lose a count on each reversal. > But, then it ought to lose a count > in the opposite direction when the spindle reverses again, > correcting the first error. > > I have to admit I have not done peck rigid tapping, so I > can't say if the same problem is happening on my machine. > > I have a fairly low encoder count on my Bridgeport, 324 > counts in quadrature/rev. > What is the resolution of your spindle encoder? > Depends on which gear Jon. I have switches on the knob, and I switch encoder scales in some hal stuff according to the switches. The effective scales are something over 7000/1 in high gear, and a similar fudge factor over 14,000 in low gear. This was determined by recording the encoder count at turn 3, stopping the count at turn 103, and subbing the first count from the second and dividing by 100, in each gear. But thats never changed as I always tap in low gear. And I've got taps up to 7/16" in my tap hats. > I do lots of rigid tapping in aluminum with fairly small > taps, 2-56 up to 10-32 or so. > I have no issues with torque on these, and I only have a 1 > Hp spindle motor and VFD.
I've got more than that but a limited geardown. Its a 90 volt, 9.7 amp motor when driven by the OEM driver which got ripped out with prejudice 6 or 7 years ago, replaced by a homemade 127 volt supply good for about 20 amps before it trips the circuit breaker, but your pwm-servo is set to limit at 17 amps. On a quick reverse, I hear the iron in the motor chirp from that limiter, but the reversal is contoured by a limit3 in front of your pwm-servo, in both directions, to stop z following errors at reversals. I could reverse faster, but z can't keep up. In low gear, the spindle motor inertia is the big lag, so turnaround times are about 400 milliseconds running wide open in either gear. At tapping speeds, 500 or less, 100 milliseconds and no chirp. The turnaround from motion is blocked by some hal stuff, detected by compareing the direction from motion to the direction its turning by an xor. That grounds the limit3's input and that ramps the motor to a stop which runs the supply up to about 165-170 volts. The stop is detected by a retrigeerable watching an encoder leg and when it times out, the reveral is clocked on thru to your driver, and the limit3's input is restored at the same time, so the limit3 ramps it back up to speed using up the over voltage in the supply long before the caps heat. And the house lights don't blink. > I do use Alum-Tap, which is a truly magic tapping fluid. > You can EASILY feel the reduced torque > when hand tapping aluminum, maybe half the torque as when > using cutting oil. Not stocked locally. Wish it was. > One other issue, could there be backlash in your Z drive? I > have less than .0015" backlash > in my Z drive. Last time I checked last fall mine wasn't up to 2 thou yet. This could also be related to the post itself being out of square which has the obvious effect of pushing the tap sideways as it descends into the hole. I need to buy a circular square, grab the post with the hoist I use to move that bs-1 around, and pull its bolts and ream the holes one size bigger so I can adjust it plumb like it should be. Cheap chinese mill. Thats been on my todo list for 3 or 4 years since I discovered it wasn't square. It might even need a reynolds wrap shim to plumb it for and aft too. Won't know till I get the square, or make one on the sheldon. But I don't have stock that big. > I can easily imagine Z axis backlash could > be a greater issue than which side > of the encoder pulse it is counting transitions on. > I don't buy that at all, given the encoder scale(s) involved. > Jon > > > _______________________________________________ > Emc-developers mailing list > Emc-developers@lists.sourceforge.net > https://lists.sourceforge.net/lists/listinfo/emc-developers 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-developers mailing list Emc-developers@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-developers
