Stepper size and max speed

[DAlgie]

So after I upgraded my CNC lathe to the latest Mach release, forgot which one it was, there was something different about how it puts out its pulses, and I had to lower the max rapid speed to keep it from stalling. I used to have 55"/min rapid on the Z axis, now all I can get away with is 35"/min. SO, I was thinking of going to a larger stepper motor on the Z axis. It has a NEMA34 640oz/in now, I could easily go to the longer 1200 or so one. I know, more voltage is the answer but I am stuck with the 42 volt system I have now. Question is, will the larger torque stepper give me more speed on the same 42 volt supply? Thanks to all.
                                        DaveA.

[ger21]

It's far more complicated than just asking. Typically, the bigger the stepper, the slower it will spin.

What you need to know, though, is will it have more torque at the rpm that the current stepper is stalling at.

You need to look at torque curves for the two motors to compare them.

[RICH]

There are problems with torque curves, none may be  available for the motor, the curves are for 24 or 36 volt so not representative for higher voltage systems.
RICH

[DAlgie]

Yeah, no torque curves available, or that I can find anyway. Was really wondering if anyone had tried this same idea, and if it helped or not, doesn't sound like it's worth trying though. My AB 8400 mill has 200 in/min rapids and this lathe looks pathetic alongside that. But it works, so I can't really complain.

[RICH]

wondering if anyone had tried this same idea

Are you meaning comparison of one machine to another?
My comment would be that you can make a "relative" comparison.  ie; Given the same electronics and gearing, you can say that the mills table is larger than the lathes carriage, so in that sense, the preformance should be similar. There is a difference in the cutting load, torque required for bearing and ball nut load, and motor specifics that come into play like Gerry replied.

RICH

[DAlgie]

No, meaning a simple 'apples to apples' comparison, will a larger stepper motor, on the same voltage, drive ANY machine at a higher max speed, than a smaller motor? No other reference needed.

[ger21]

Depends.
If the max speed of the machine with the smaller stepper occurs at a low stepper rpm (~300), than the larger motor should be faster.
If the max speed of the machine with the smaller stepper occurs at a high stepper rpm (~1000 or more), than the larger motor might be slower.