That depends on 2 things, Martin. 1. And likely the most important by far, is the coil inductance.
A motor with only 2 millihenry's of inductance can achieve full coil currents quick enough to have usable torque at 500 rpms. The same motor frame, wound for the same starting torque but has a 15 or more millihenry inductance will use less operating current to run at 5 rpm than the 2mh one, and will use perhaps 1/3rd the current. But it will be all tapped out and may not ever get to 500 rpms under zero load. 2. The supply voltage fed to the driver, raising it will get the current flowing quicker, but trying to make that 15mh motor turn as a usable high speed motor, could take more voltage to overcome the inductance than the driver can tolerate. That has a nasty tendency to break the mirror and let all the smoke out. I replaced a 1600oz/in motor used as the Z drive on a G0704, with a 950oz/in. Where the high inductance of the 1600 fell over was at about 27 ipm. The newer, smaller motor with a new self-contained psu/driver, can now run that close to 40 lb head up and down the post at 70+ ipm and doesn't break a sweat even when rigid tapping. Look at the Clearpath torque curves, they fall over at a rate virtually the same as a good stepper. The 'real' substitute will generally be a decent BLDC 1kw servo motor. That is what the much higher priced MC series is, with a 3 phase drive built in. Gene, Thank you for educating me. I couldn't find the torque curves for the Clearpath drives, your google-fu must be better than mine <grin> What TPI does the lead screw Z axis on your G0704 have? I thought the 1810oz/in stepper was probably overkill in the spindle application, and I did wonder if a more modest size stepper would work. The people that have done this claim to have tried all sorts of sizes before arriving at that. The only requirement is to thread mild steel at 0.005" pass and a spindle speed of 150 to 500 rpm (depending on size) and to completely replace the Sherline motor for turning operations. Do you have a link to the 950oz/in you used? Cheers, Martin ________________________________ ------------------------------------------------------------------------------ _______________________________________________ Emc-users mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/emc-users
