Thank you, all of you. The step up transformer is a great idea. I’ve been looking for a single phase 5 HP motor, and have found one but maybe going with the rpc and transformer is the way to go. I’ve had both the electronic, and rpc and have had good results with both. Both never used one at 440.
There are figures .. and other figures . .as to what "real world" rating a transformer needs to have to be effective for machine-tool loads and an RPC.
One workable rule-of-thumb to insure it isn't too small as to restrict max power or run overly hot is two KVA per load HP. That isn't the same as laboratory physics - the KVA to "motor HP" calculations online come out to only a bit over 5 KVA for a 5HP load motor of typically less-than-perfect efficiency and power factor.
But it WORKS better for easier starting and at sustaining higher loads smoothly to go a bit larger and utilize - for example - a stock 10 or 12 KVA 3-Phase transformer off an RPC with 10 HP idler connected for 440 VAC use.
My one, for up to 7 HP loads - is a Phase-Craft start/run control box + 10 HP Weg idler. OTOH, the transformer is a near-as-dammit 1:1 EGS Delta-in, Wye-out "drive isolation" transformer so I can take the Delta off RPC or Phase-Perfect and derive a new "local" Neutral.
"Wye" is optional. I don't think you have a need for a Neutral, your machine? I'm simply
allergic to both floating AND "corner-grounded" Delta.
I also don't need 440, but it does have the advantage of requiring lower-ampacity wire, and running dual-Voltage motors a tad cooler than they run in their 220 V configuration, so "run what you got".
With THIS lathe, you still have the advantage of LOTS of geared-ratio selections, so should not suffer at 7.5 HP idler and 7.5 KVA, and might "get by" even comfortably so with 5 and 5 with an unloaded start.
Transformers don't waste
much, but they can briefly look like pretty heavy starting loads, so don't grossly oversize one, either.
NB: IF.. you have no other 3-P loads @ 220/240 VAC? Such as coolant-pump replaced with a 1-P unit (which I do..) then a
single-phase transformer on the input side, RPC's idler run @ 440 VAC off its secondary works, too.
As a 2:1 step-up ratio is better-suited to a full-isolation transformer than a boost "autotransformer", used 3-Phase ones may be easiest to source locally at good prices. They tend to be HEAVY, so shipping can be expensive.
Either way - you'll also need (up to..) "600 Volt Class" goods -
(wire, disconnects, fuses, CB, and such) - on the 440 VAC side, whereas the input ~ 240 VAC is still within the (up to..) 300 V class.