Komatiad, my understanding is the spindle would become an A axis, with a separate milling head bolted on elsewhere.


Quote Originally Posted by Valfar View Post
My thoughts were to use 2 separate motors, and couple them both to the spindle: one geared up and the other geared down. But only one would be powered on and running at a given time. At the same given time, the other one would still be rotating, but driven by the spindle (as it won't be powered) - the spindle would rotate due to the other one.
That wouldn't work. Say you have the low speed with a 10:1 ratio, and the high speed direct drive, that would mean at high speed the low speed motor will be getting driven with a 1:10 ratio, so at 3000rpm, it would be doing 30'000rpm.
I would create a lathe profile (in Mach3 for instance) and run the machinery in lathe mode, with the high RPM / low torque servo power on (and the other servo off).

When milling is needed, I would shut down everything, create another profile (mill profile) and run the machinery in milling mode only, but this time with the low RPM / high torque servo powered on (and the lathe spindle servo off, which would still be rotating due to the other motor), configured for the 4th axis role.

The lathe and mill would share the X and Y axis steppers.
There is a Swapaxis function within Mach3 that you probably want to look at.
If you've not already seen it, you may want to have a read of this thread - http://www.machsupport.com/forum/ind...c,11422.0.html

A possible option, depending on if you don't need the 4th axis to move while machining, is to add a brake, as then you don't need lots of torque to hold the spindle. You just need enough torque to locate the spindle, then use the brake to hold the spindle.