Getting an old 3 phase lathe running again

[Cooper]

I have just retired and have a very old Union Graduate lathe, which I rescued from a school I worked in, which closed well over 30 years ago. I have assemble it and would like to get it working again. The motor is 3 phase and the connection block looks very complicated, not at all like the ones in YouTube videos about converting 3 phase to single. Is it possible to get the lathe working on ordinary mains electric without too much expense and what should I do. (I enjoyed teaching wood turning but always had technicians or ILEA electricians to sort out what was outside my comfort zone.)
Thanks
Martin

 

[curtisrider]

I whacked a single phase motor into both my 3 phase lathes, they are cheap and plentiful.

 

[Cooper]

Thank you Curtisrider . It is very tight inside the casting where the motor sits. Do you think the mounts on a new motor will fit the old fixings and will it take the old pulley wheel without too much trouble? Where did you get your motors?
Martin

 

[CHJ]

The alternate is to obtain a suitable Single to Three phase invertor, this would mean no problems with pulleys etc. and with the added benefit of variable speed and reverse functions.

Send your motor details to Myfordman of this parish and I'm sure he will point you in a the right direction to get you sorted.

 

[woodpig]

It's easily done with a suitable motor provided you're happy to swap a few wires over in the junction box and add a capacitor. I ran a three phase milling machine on single phase for a couple of years without issue. Not all motors are suitable though, they need to be dual voltage and be available to swap the wiring from star to delta in the junction box.

 

[graduate_owner]

I agree with the three phase option, but the motor must be dual voltage to enable it to be connected in delta mode, else it must be changed. You are right in saying there is not much room, but I suspect a three phase motor will be more compact than a single phase motor of equal power.
A single to three phase inverter will cost around £150 - £200 depending on whether the envlosure is ip rated (recommended, to keep out dust and moisture). I would avoid far East imports. I bought mine from willpowerelectricalltd, invertek make, made in britain. You will find plenty of information on the web about connecting the motor. A dual voltags motor will have 6 terminals. If yours doesn't then as I said it will need to be changed, so you will need to consider mounting holes, shaft diameter etc.

K

 

[Cooper]

Hi Graduate Owner,
It is a Gryphon motor, the plate on it says: 50∿ Type PROT, 400/440 volts, Cont. rating, 3PH, RPM 1420, 1.3 F.L. Amps, 0.75 H.P, 50 deg C Rise.
I think all this means that it not a 240-400 Volt motor. It is an old machine (1950/60s) and the holes and shaft probably won't match a modern motor. I think it will need an invertor that can raise the voltage from 240 to 400, from single to 3 phase.
Would an invertor like you mention run my machine or are you saying that it needs a new motor? Sorry to be obtuse but this electrical detail is new to me.

Thanks
Martin

 

[dickm]

Having an old imperial sized motor can actually be an advantage! If you know where to look, or have very good luck, you can pick up such motors very cheaply BECAUSE they don't fit more modern kit. The 2kW motors on my Lurem cost less than £60 for the two and are still going strong after 20+ years of fairly regular use.

 

[graduate_owner]

Hi Martinr,
It certainly sounds like your motor is not dual voltage. You have a few options.

You could buy a three phase CONverter which will give you 3 phase but not variable speed. There are two types, static or rotary. Static are cheaper but do not give such a good approximation to true 3 phase, and a 1 HP motor would probably only give 3/4 HP output. Rotary converters are basically static converters with the addition of a balancing motor ( itself a three phase motor, rated at higher HP than the load motor). By changing over two of the wires you can reverse the direction.
You can find these on ebay, static converters at about £400 for 1.5 HP. Rotary converters cost about £600 for the same power. Not a cheap option really, although it becomes feasible if you have other 3 phase equipment. It is however the easiest option because you can just plug and go.

A three phase INVerter is the type that gives variable speed but needs a dual voltage motor as they give out 220v 3 phase. I have heard of inverters having built in transformers which give 440 v 3 phase and would run your 440v motor but I don-t know anything about them I'm afraid. I don't think motor mounting would necessarily be a problem. If the bolts don't line up you could perhaps mount the new motor to a ply sub base and fix the ply sub base to the lathe. Then it's just the pulley to fit to the new motor shaft, again might fit or might need reaming to fit, and ensuring it all lines up. An inverter would be around £150 in a suitable housing. That is the best way to go I think. You will have a really nice, well respected piece of kit at the end of all this messing about - I love mine. The spindle thread is the same both sides (apart from right / left hand thread) and you can get a dual threaded chuck which fits both sides - saves getting another chuck or an adapter if available ( which is unlikely since it is not a common thread). Your lathe is solid enough for professional use and can run all day. Of course you could just sell it on and use the money to buy a hobby rated far East one with a recommended Maximum use of 100 hours per year, but I certainly would not. Keep the beast, get it working and enjoy it.

Just one more comment - if you go down the inverter route, you will need to bypass the switchgear and safety microswitches because the inverter must connect to the motor directly, and you control the motor from the inverter front panel or using remote cabling. Again this is not a problem ( unless you are employing someone and H&S are involved because of safety switches). The remote cabling is low voltage so you don't have to worry too much about that.

So basically it's source a dual voltage 3 phase motor of about 1 - 1.5 HP first, then you can see about mounting / pulley issues, then get a suitably rated inverter. Wire up and away to go using default parameters on the inverter. If you feel unsure about the wiring then obviously get appropriate help - don't take risks.

Any more questions- just ask. I'm not an expert but I do have a graduate bowl lathe, a 3 phase inverter and a rotary converter ( for my colchester metal lathe, because I wanted to keep the switchgear).

Edit - try to get a motor that is rated as 1425 or so rpm rather than 2850.


K

 

[fred55]

Can only agree to those who know much more than me - But like you I retired from school and took one of the 3ph union grads that where not being used (star delta motor) - I bought a cheap £80 inverter from ebay and coupled it straight to the motor it worked lovely for 18 months and not knowing much about IP dust/water protection the cooling fan started to squeak/rattle. The inverter now sits inside a box with a small filtered fan blowing air through it. So what I say is get it running and see how you like it and how much you intend to use it. I'm at the position where I enjoy the lathe so considering upgrading the inverter (IP) and hopfully a larger motor 1.5 or 2kw.

 

[graduate_owner]

I would like to upgrade my motor too, which is why I bought a 3HP inverter. I think the current 1 HP is a bit too small, and I would like a 2 HP, especially since I bought the graduate for bowl turning. Another job to do one of these days.

K