Hi Gene, Thanks, Warning, Ramblings have been edited for size. <GRIN>
> Warning, generalized ramblings of an old fart follow. .<SNIP> > Usable torque was pretty much gone by 2000 rpm. > I agree. Since the resolution for the spindle isn't nearly as a big a deal for a spindle I thought I'd use pulleys to step up the speed. Unless I'm using the spindle as an indexing head a minimum RPM of 30 is more than reasonable for any large diameter threading that fits on that small a lathe. I've found steppers don't do much better after about 700RPM. So if I want 5600 RPM I'd have to go 1:8. A stepper excels at a smooth 3.75 RPM and has the torque so that a smooth 8x=30 RPM wouldn't be an issue. Or just change belts and pulleys for the different speed. > Software step generation suffers from latency which causes less than a > steady frequency, and this detracts from the usable torque because the > motors speed is being asked to vary as much as 20% in a single > revolution. On the x86 platform, the next slower software step frequency > is nominally 20 Khz, but thats such a huge percentage change that > neither is likely to be a usable step frequency for software generation. > Because of that, the practical limit is lower, probably under 5Khz for > stall free operation. Thats about 600 Hz as you hear it from the motor > when using a /8 diviser. Hardware (FPGA) generation raises that "bar" > quite a ways. /16 to as much as /64 is usable then. But a /64 explores > the speed limits of the opto's in the drivers, limiting the top speeds. I run the ELS at 20kHz. I've also found about 700RPM as the limit with the on board 8x micro-stepper. > I only have one nema 34 motor, on the Z axis of my GO704 mill. Using a > 5i25 card, and /16 as the microstep divisor, it has a huge resonance at > one relatively low speed, but can happily run at 3x that speed while > lifting the head of the machine. How much of that resonance is the > rather filligree mounting of this particular conversion kit I haven't > determined. I would love to have been able to install some dampers, but > the motors supplied are single ended shaft. That's one of the questions I'd not yet posed about using a stepper for the spindle. On my JGRO CNC at some speeds they do growl. I wonder if that would translate to surface finish even with a belt drive. The spindle and chuck tend to be a pretty good damper though. <SNIP> > Cheers, Gene Heskett > -- ------------------------------------------------------------------------------ _______________________________________________ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
