[teglberg]

Hey guys (and girls - if any..)

I was wondering...

1: - is it possible to use a stepper motor (was thinking Nema34) as the main spindle?

2: - is it strong enough? (would like to have the ability to cut steel)

3: - if so can it then be connected as the 4th axis so that it can be indexed?

4: - do you have any experiences or thoughts about the project?

5: - can it even run (continously) at high speeds (with acceptable torque) - maybe with belt/ gearing?

by the way, it's a "simple" 3 axis mill I'm building... (if you could just answer one or some of the questions I would appreciate it!)

[109jb]

1- No. Steppers lose torque as speed increases. above 2000 rpm or so it drops off fast
2- No
3- No. as a spindle the way it is commanded would ahve to be different, but it could be indexed. Would likely require special programming.
4- No experience, but I wouldn't try it with a stepper
5- Steppers can definitely run continuously, but not for a spindle.

[ger21]

No, no, no, no, no.
The faster a stepper spins, the less torque it has. At high speeds, steppers have almost zero torque.

[teglberg]

ok., guess that's off the table then.

any recomendations on choosing a spindle then? guess I'll go with VFD as everyone else then
- can VFD spindles spin both directions?( - you can't do thread tapping with those can you?)

as said I would like the ability to cut steel, what are the price range/ cost then?

[A_Camera]

ok., guess that's off the table then.

any recomendations on choosing a spindle then? guess I'll go with VFD as everyone else then
- can VFD spindles spin both directions?( - you can't do thread tapping with those can you?)

as said I would like the ability to cut steel, what are the price range/ cost then?

Cutting and tapping steel means low RPM and very high torque. So, forget about cheap Chinese spindles. Also forget about cheap DIY machine. You need weight and rigidity, and a lot of that. A machine like that weights over a ton, so be prepared for very high costs as well. Personally I am not even dreaming about steel.

Yes, a VFD can turn the spindle in any direction. Rotation direction change with three phase motors is very simple, you just swap two phases and the direction is changed. That's an easy task for a VFD since the phases are just "faked", created by electronics inside the VFD. But again, tapping steel demands very high force at low RPM, which can't be done with cheap spindles, at least not the ones which run up to 24k RPM. Those spindles lose torque at very low RPM.

[teglberg]

Cutting and tapping steel means low RPM and very high torque. So, forget about cheap Chinese spindles. Also forget about cheap DIY machine. You need weight and rigidity, and a lot of that. A machine like that weights over a ton, so be prepared for very high costs as well. Personally I am not even dreaming about steel.

Yes, a VFD can turn the spindle in any direction. Rotation direction change with three phase motors is very simple, you just swap two phases and the direction is changed. That's an easy task for a VFD since the phases are just "faked", created by electronics inside the VFD. But again, tapping steel demands very high force at low RPM, which can't be done with cheap spindles, at least not the ones which run up to 24k RPM. Those spindles lose torque at very low RPM.

Okay the tapping isn't necessary, but I would still like to cut steel (occasionally) can it be done within a reasonable budget? The structure of my machine is very rigid...