Bob, thanks. I run the lathe from a phase converter now and it runs
great. So the reasons for putting a VFD on it are of minor nature,
such as making the lathe quieter, and having a working but cosmeticaly
flawed 5 HP VFD that is hard to sell (cracked front cover).

The issue with "switch between the drive and motor" is the two speed
forward/reverse lever on the lathe.

The lever lets me switch motor speeds on this reversible two speed
motor, REV2/REV1/OFF/FWD1/FWD2.

If I put the lathe on the VFD, everything would work well, I would
switch the VFD with the ON/OFF/BRAKE lever connected to its control
terminals.

It would work great, except:

This is all problem AS LONG AS I do not try to flip the
REV2/REV1/OFF/FWD1/FWD2 switch during running. If I ever do so, the
drive may be ruined as I would switch the motor live with VFD powered.

That is my issue. If I could, somehow, keep the drive safe when
accidentally flipping that speed selector lever during running, I
would be happy.

Sorry for starting another thread on this, my news server refuses to
show the old thread for some reason.

I re-wired the drum switch on my lathe to supply control signals to the
VFD and everything is happy. It was not too difficult to do the wiring.
You could probably even get the two speed setup depending on your VFD.

I have a Clausing 1300 which I think is a similar size but different
model machine than yours.

If you really, really don't want to re-wire the switch, how about turn
the switch on and take the handle off it? That would make it unlikely
that you would switch it off while under power. Use the VFD for
direction and speed control.

Good Luck,
BobH