I’m sure it would work. It seems like almost anything will work to some degree. I was just wondering if my thought process was in line. I want to build one that is safe and reliable
I did mine all brand new, Jim's Phase-Craft control, a ten HP Weg. Figured it was actually a "once in a lifetime" spend, so no compelling reason to invest time I did not have spare trying to find a used motor, haul it or ship it, clean it, put new bearings in it, mebbe paint it - or basically mess-with at all. Other fish to electrocute, and I am waaay behind schedule on all of those arredy - a nicer mounting (its own wheels) for the RPC included.
Ability to add another 5, 7.5, maybe even a 10 HP as supplementary idler for at least handling load motor starting inrush is plenty. My worst-case is about 7 to 7.5 HP load, main spindle and traverse/rapids combined. Only the main drive motor matters as to starts. Knee is only 1.5 HP.
It is rare to
run a load-motor - of any size - on a machine-tool hard up against nameplate FLA, anyway. Half or even LESS, is far more common. A table saw is more likely to hit its peak than a lathe or mill is.
Even if I NEEDED 15 HP or 20 HP, I just didn't want to have to START an idler larger than 10 HP in a single chunk. A "supplementary" idler after all, does not NEED a supplementary RPC control. Only a contactor.
The power "wasted" by an RPC, idle or loaded is not worth much worry, either. VFD and DC drives are only around 95% efficient, Phase-Perfect 93%. WTH - even a
transformer has measurable losses.
An RPC's "efficiency" isn't really enough different for that part of its characteristics to greatly matter.