On Sunday 09 May 2010, Jon Elson wrote: >Hello, all, > >I just added a DAC for spindle speed control to my Bridgeport. For >years, I just had forward and reverse contact closures to the VFD and a >manual speed pot. Now, I have a DAC channel from EMC to the VFD. I can >start the spindle with an MDI entry like M03 S2500, but when I try to >start the spindle with F9, it sends the spindle forward contact closure, >but the DAC had been reset to zero. > >Is there a way to make the F9 key use the last spindle speed setting? > >(In other results, I have been doing a bunch of rigid tapping on 2-56 >and 6-32 holes. The only problem I had was finding out that my $8 >spiral-flute taps are not good for deep holes. They bind up. A spiral >POINT tap goes through like butter. 1000 RPM for 2-56, 800 RPM for 6-32. >My only problem is all the reversing makes my VFD get overheat alarms, >even with a fan on it. I probably need to get a bigger VFD.) > >Jon
Maybe Jon. Maybe. How long are you allocating for the stop from motion? I have a 20 watt 8 ohm resistor across the motor when the drive is shut off. So the spindle turns maybe one full rev in stopping from wide open in low gear. You need to let the motor come to a full stop, dumping its energy into the 'suicide' brake resistor, before applying reversing power. In my case I wrote a test loop that I've since lost in a re-install, that sent it to full speed in about a second, stopped it killing about .5 seconds, then sent it to full speed in the other direction. I let it do that for about half an hour and nothing complained except the motor, which was quite warm by then, and the fuse, a 2 amp quick blow that fatigued open from the repeated heat pulses, which was what actually terminated the test. This however was after I had blown the hexfet in the micromills spindle motor controller, and had replaced it with one from a handy, already kaput computer psu. This one has a current rating several times the OEM part, and about 2x the voltage rating, so the driver transistor is now in greater danger than it is. I could probably raise the fuse to 3 amps now and get away with it but I'm not yet out of 2 amp fuses for it. ;-) Bigger motors of course would need correspondingly longer times I'd assume. PM dc motors I am told can be field damaged by those braking currents if they are simply shorted to stop them, so one might want to query the maker and ask what is the minimum ohm's for this braking resistor. Turn around times would have to be extended if the stops aren't so sudden. -- Cheers, Gene "There are four boxes to be used in defense of liberty: soap, ballot, jury, and ammo. Please use in that order." -Ed Howdershelt (Author) Mommy, what happens to your files when you die? ------------------------------------------------------------------------------ _______________________________________________ Emc-users mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/emc-users
