[keebler303]

A welder is going to give you noisy power with a large ripple voltage.

Why not just buy a simple single phase supply and be done with it?

I think this would do just fine: PS-15N70 - 1500W 70V Power Supply - AnTek Products Corp

Not appreciably more expensive than your welder idea and requires no tinkering with capacitors or anything...

[cnc1000]

That probably looks like a good solution. In sizing the power supply, I'm assuming 7A per phase, but I have two phases and that 7A is the rating for full step operation and in that mode, you always have two phases running 7A at a time. They commutate around, but always have 2 phases on. Since I will be running in chopped mode, which looks like a sine wave, the actual current would be the rms value of 7A, which is 5A per phase, roughly. So each of 3 motors would be taking 10A. If all 3 were running at once (unlikely), then I'd need 30A capability. Since I only expect to run 2 axis at a time at most, 20A would probably be fine, so long as there is temporary capability to exceed the 20A specification for the supply.
If someone has a better technical explanation, I'm all ears.

On the welder, I agree that the DC output is probably nasty, but not as nasty as you would guess, since it is an inverter technology, not simple transformer linear supply. I would put some large capactors on the output, anyway.
Thanks,
cnc1000