On Tuesday 02 February 2021 22:24:16 John Dammeyer wrote: > > From: andy pugh [mailto:bodge...@gmail.com] > > > > On Tue, 2 Feb 2021 at 17:22, John Dammeyer <jo...@autoartisans.com> wrote: > > > What's a CNC slotting head? > > > > It's like a slotting head, but CNC :-) > > > > The idea would be to have a CNC controlled tool rotation combined > > with the conventional reciprocation. > > > > -- > > atp > > OK. Let's see if I have that right. My Spindle is driven (well will > be as it's currently still 0V-10V) with step and direction. There > will be an index and of course encoder on the spindle. > > Once I have step/dir instead of PWM/DIR I should be able to tell the > spindle where I'd like it to be. So if I have a rectangular punch > held and keyed in some repeatable fashion (better than the R8 pin) > then I should be able to tell it to turn to 45 degrees and then move > down. (or knee move up). > > The motor holds the spindle pretty well solid. In fact annoyingly so > because unless I disable the AC servo it won't let me turn it. I > imagine though a brake is probably needed to ultimately hold it really > stiff. > > Is that what you mean? > > But can you actually configure LinuxCNC to both run spindle as an RPM > axis and also a positioning axis? I realize the loop is closed for > tapping but 60 teeth per rev for the encoder isn't the same as 3600 > for the nearest 10th of a degree. > > John
Correct John, you will need a higher ppr encoder. My spindle encoder is actually on the rear of the motor so it is subject to the backlash in the plastic gears, but its a 1000 ppr encoder whose "scale" is switched by tally switches on the shifter knob, from my ini file: ENCODER_SCALE_H = 7161.61 ENCODER_SCALE_L = 14095.34 That is per revolution so I could get pretty close to a tenth in low, but the holding power within that tenth wouldn't be that great as its a ball bearing PMDC motor controlled by a pwmgen. The BS-1 servo rests well within that tenth when stopped, but accuracy is subject to the backlash in the bs-1's worm and is quite slow getting there. Top speed with that PMDC 100 watt estate gate motor driving it is about 3 rpms. That driver motor has an encoder which checks out at 666.66666666667 counts/degree of the bs-1. For calibrating the scale I put a home switch on it and put some heat in the motor by measuring 100 cycles of the rising edge of the home switch. As presently setup, it never quite gets to balance, friction stopping it an arcsecond or so early. The pwmgen driving a pair of BTS-7960's on a $6.40 driver is still outputting a very narrow pulse, well under 1% on time when it stops. I am not done piddling with the PID and the offset. I need to set its scale from the error direction, not the error itself. But other stuff has got in the way like losing the video on the 6040 about 18 hours after I updated it to buster. 4 identical off lease dell's with i5 cpu's & 4Gigs of dram s/b here tomorrow night. When I get done they will all be running from our buster image. Stay safe and well 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 Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
