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Help with lathe motor, running hot and then smoking..

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Matt Mackeson25/01/2021 12:43:43
10 forum posts
4 photos

Hello all,

I am in the process of restoring an old Schaublin lathe that hasn't been used in a while.

I have recently turned my attention to the motor, which I had had running previously but only for a short time.

Here is the motor plate for ref.


Apologies for the rotational issues, they are the correct orientation on my computer!

As you can see it is a 240 V single phase unit.

This is the current state of the wiring at the back of the motor, it is connected to a 3 position, forward and reverse switch.


From my limited understanding, the cylinder is a starting capacitor, which I know to work as the motor does start when plugged in.

It then runs very hot and started to smoke so I quickly un plugged it.

Again, from my limited understanding this unit is the running capacitor:


It doesn't have any markings except for ISSA.

Could a fault in this be the reason for the motor to run so hot or will it more likely be an issue with the windings?

I imagine it is probably difficult to know without someone with more knowhow than I possess looking at the motor but I thought I would ask and see if anyone could shed some light on the issue.

Many thanks,



Edited By SillyOldDuffer on 25/01/2021 12:49:30

Ian Parkin25/01/2021 12:54:18
900 forum posts
215 photos

I'm fairly certain that the device marked ISSA is a timer to switch the cap that you have in and out of circuit when needed

Rather than having mechanical switches inside the motor ( centrifugal switch)

Brian Morehen25/01/2021 13:18:22
142 forum posts
11 photos

This looks very much like the Centrifugal Switch has stuck the part of this switch is the sleeve that moves on the armature shaft disconnect the start winding and changeover to the run winding . when this does not change the motor runs hot very quickly and starts to smoke , You are going to have to dismantle the motor to check for problem does happen when a motor has not been used for some time.

Regards Bee.M

Hollowpoint25/01/2021 13:24:04
402 forum posts
51 photos

First thing I'd do is get yourself a can of contact cleaner and give everything a good clean inside out. Check everything is free and rotates smoothly. If not change the bearings, lightly oil any mechanisms, check the brushes and armature. Replace brushes if needed. If is has a fan make sure it isn't just spinning on the axle. Check for loose wires. Reassemble and try it.

not done it yet25/01/2021 13:47:18
5626 forum posts
20 photos

Good luck, but I think the motor is likely ready for rewinding/replacement. Can’t be sure but it will be lucky if it is recoverable.

Smoking likely means one of the windings will be short circuited by now - enamel insulation melts before starting to smoke. No brushes in an induction motor.

Dave Halford25/01/2021 14:08:26
1291 forum posts
12 photos

To be honest is anything electrical lets the smoke out it's too late to faff about with.

John Haine25/01/2021 15:38:10
3661 forum posts
206 photos

I think I would treat the lathe to a nice new 3 phase motor and VFD, it deserves it.

Hollowpoint25/01/2021 20:14:34
402 forum posts
51 photos

A bit defeatist.

I had a smokey motor that had been sat around for a long time, turned out it was just dried on oil and dust burning off. Considering a new motor will likely be £100+ you have little to loose by having a look inside.

Matt Mackeson27/01/2021 00:42:33
10 forum posts
4 photos

Thanks for all your replies. Today I sucked it up and dropped it off with a local electric motor repairer. (in a very Covid safe manner)

He is going to take a look at it and let me know what needs doing and whether it will be economical to do so.

He did say that the old mechanical centrifugal switch must have broken at some point, and that the mystery black box was an electronic replacement.

If it's not worth repairing I will search out a 3 phase equivalent.

Ian Parkin27/01/2021 07:34:49
900 forum posts
215 photos

Just to say that in post 2 i did say that it was an electronic starter switch so it wasn’t too much of a mystery

not done it yet27/01/2021 08:18:49
5626 forum posts
20 photos
Posted by Ian Parkin on 27/01/2021 07:34:49:

Just to say that in post 2 i did say that it was an electronic starter switch so it wasn’t too much of a mystery

Yes, but... Even if that part was faulty it was not where the smoke was coming from, that is likely to write the motor off.

Ian Parkin27/01/2021 08:28:04
900 forum posts
215 photos

But it will be the timer switch that has caused the smoke to be let out.

I've never found having motors repaired/rewound economical untill the new motor gets to being more than £1K or so.

i've had motors rewound that are £60k new

on a motor such as Matts just buy a new one 3 phase and a small VFD and your done for less than £200 with a lot of benefits over the original motor

Matt Mackeson27/01/2021 11:10:13
10 forum posts
4 photos
Posted by Ian Parkin on 27/01/2021 07:34:49:

Just to say that in post 2 i did say that it was an electronic starter switch so it wasn’t too much of a mystery

Yes sorry Ian I was only calling it a mystery as that is what it was in my OP.

I may very well just replace it with a 3ph and VFD setup, but will wait to hear back from the motor man.

noel shelley27/01/2021 12:59:13
381 forum posts
9 photos

A 1/2Hp 1425 brooks motor will do a good job. Too small for the myford S7 so that should help to keep the price down & common enough. I find it hard to understand why one would replace a simple and almost bombproof motor with an expensive and complicated box of electronic tricks which if it is hobby rated may not last long. An industrial unit will be good but cost many shekels ! If the lathe was designed with a single speed motor do you need a VFD ? Noel

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