On Thursday 16 January 2020 12:42:01 Gene Heskett wrote: > On Wednesday 15 January 2020 22:59:20 Jon Elson wrote: > > On 01/15/2020 09:10 PM, Brent Loschen wrote: > > > In addition to the split pulleys, my "mechanical" concerns > > > are more along the lines of the heavy duty electrical > > > contactors clunking every time the fixed speed, 3 phase AC > > > spindle motor is called to switch back and forth; > > > increased heat in the motor windings due to those > > > reversals; and the air powered, mechanical spindle brake > > > snapping on and off hundreds of times. Yes it was very > > > tempting, and yes, I'm sure some of my concerns could be > > > mitigated, however I feel that this old mill (cira 1985) > > > just isn't the right tool for the job. > > > > OH! I'm not sure you can do rigid tapping by plug-reversing > > the motor on mains power. At our shop, where the mills run > > off 480 V mains, the plug reversing is so fast you can't > > even hear it. I doubt any Z axis could keep up. But, don't > > worry about > > the motor, it can handle this "abuse". I do rigid tapping > > using a VFD and analog spindle speed control. Even with that, > > I generally reverse the spindle in about 3/4 second, from > > 1000 RPM forward to 1000 RPM reverse. That is slow enough > > for the Z axis to follow. > > > > Jon
Spelling correction, tab=tap > Whereas my G0704 is so fast I had to insert a limit3 to shape the > turnaround so z could follow. The slowdown is not noticeable and the > reversal is still around 1/2 second at the speeds I use. But I have to > be carefull with blind holes, subtracting the overshoot else the tap > bottoms and breaks. And I've not yet incorporated the gear shift > effects into that shaping, needed because of the motor armatures > increased effective mass due to the armatures 2x increase in speed in > low gear. > > A work in progress IOW. I have some hal code that measures this > overshoot and displays it in the pyvcp area, both of the turns and the > actual distance traveled, in the gui in the Sheldon's config, but > haven't incorporated it into the G0704 yet. Need to get that done, and > a tool holder made for the lathe to carry a top-hatted tap. > > Slowed progress because of the heart attack, but feeling perkier now. > > Currently working on the base shoe to install the BXA on the Sheldon, > its a blond one bigger than the piston post I'll toss. The base shoe > is supplied way oversized so it will fit any compound and I need to > make it fit the spacer where the compound used to live. LinuxCNC is > its own compound. > > Let me describe how the reversal works here in 3 machines. TLM can do > it too. > > 1st, the direction change coming from motion, going to the motor > controller is blocked by a sample-hold while the limit3 is shaping the > motor slowdown, decaying to an effectively stopped spindle, which is > detected by a retriggerable timer timing out which is fed from encoder > A's pulse. > > That timer timing out then refreshes the sample-hold which allows the > direction signal thru to the motor controller (vfd for the Sheldon), > and releases the limit3 (which has a mux2 to select zero or set speed > as input to the limit3) to charge back up to the set speed. With that > all in front of the spindle PID, and Pgain at 20+ in the G0704, and no > PID in the Sheldon, letting the vfd do it all, the G0704 is a touch > more complex. > > From that description, you should be able to achieve a reversal that Z > can follow. It all happens so fast that you aren't aware its being > dynamically controlled. On the Sheldon, belts squawled until I put new > linkbelts in it, on the G0704 I can hear faintly, the current limiter > in the pwm-servo amp I am driving its nominally 1 horse motor to about > 2x its FLA draw, getting around 2 hp from it for those few > milliseconds I can hear the limiter chirp. Been doing the chirp for > about 4 years now. > > 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
