This followed me home today.

[Pete O]

(05-27-2015, 10:52 PM)PixMan Wrote: I'd never want to give up spindle power, but that's because I love to hog metal when I have the opportunity.

Two choices on power if you don't have 3-phase coming in, RPC or VFD. A rotary phase converter is steady speed, and your idler motor should be at least 50% bigger than the total of the motors you might power up off of it. I have a 15HP idler motor feeding up to about 10HP (2HP mill, 2HP surface grinder with 1/2HP dust collector and 1/8HP coolant motor, 5HP lathe with 1/4HP coolant motor.)

One motor on a single machine is an ideal candidate for a variable frequency drive. It only needs to be rated for the total it feeds, and gives you variable spindle speeds. That can wreak havoc on hydraulic pumps or feed motors though.

I thought about a VFD, I set one up on my lathe when I got it and it has been great, I run the coolant pump from a capacitor system so it only runs half power but that doesn't matter with the pump. I wasn't sure whether this would be as practical with a mill though? There is a master switch on the side of the machine, an on/off switch at the front and an 'inch' switch on the other side, not sure whether these would all be able to be signalled into a VFD. Als VFDs in that horsepower range are quite expensive, which is the main factor pushing me toward a rotary phase converter. Also the fact that it would be a simple plug-and-play for the mill, and no additional problem with running the coolant pump.
i don't think I could swap the motors around and run the 3hp in the mill off the 4hp in a converter, the 4hp motor is actually shorter than the 3hp with a much bigger diameter. Worth exploring though.
I went to the local scrap metal bloke today to see whether he had any motors around 8hp, he said he had just sent 22 tons of motors to the smelters. Might try again in a week or so if I haven't come up with anything. Looking at the stuff he is scrapping, I'm convinced these guys have no soul! A tinker's paradise.

I just finished cleaning out the base of the machine, foul job. Will post some photos of possible sling arrangements shortly.