That's got to be a metal bridge rectifier, AKA selenium bridge rectifier. I'd be looking for an AC voltage on the two upper black leads and +ve & -ve on the other two.
According to the top diagram the bercostat is wired as a rheostat in series with the DC output from the rectifier and the clutch, via the relays.
From the 1st 2 diagrams it looks like the 3phase motor has been replaced by the clutch (it looks like the clutch may have 2 sets of coils, one forward, and one reverse) Does the motor have some sort of gearbox and clutch mechanism attached to it?
The single phase motor has an electro magnetic 24v DC clutch fitted to it but it was wired from a box on the wall with forward and reverse on a toggle switch and motor start stop on a switch on the wall almost as if the had bypassed the whole original cabinet wiring
Not sure whether to try and re wire with single phase and clutch with the lower power motor and half speeds or I've just bought this original Harrison 3 phase motor and re fit that with an inverter set up?
If I removed the magnetic clutch would the single phase motor cope with all the start stops when using the lathe in different speeds etc?
The original 3 phase are normally ok to run with an inverter/converter but don't think the motor is 240/415 3 phase
Not very good with getting my head around wiring at all so struggling with all this
The main objective is to get the lathe all working as it should with forward and reverse operated via the apron lever as it was originally
I can live with the clutch set up for now but want it all wired through original controls but. It sure how that would work with the clutch as currently the apron lever turns the clutch on and off only and forward and reverse is via a toggle switch so if re wired so lever does forward and reverse then what would engage and disengage the clutch?
Could I just remove all the DC clutch wiring/the selenium bridge rectifier and the transducer and re wire the motor into the forward reverse micro switches exactly as original but with the lesser powered single phase motor? Lose the magnetic clutch set up altogether?
I will use the reverse function a lot as it's an imperial machine and il have to reverse when cutting metric threads so it's a must for me
When the original 3 phase motor turns up il have a look inside and see if it can be reconfigured or not, at £100 I didn't want to pass it up just in case, can always sell it on if it doesn't get used