Stalling Lathe

Gents,
It's been a while since I last posted but that's another story.
I haven't had a chance to use my lathe for some time (Super 7) but now under any sort of cut it stalls the motor. I was facing a chuck backplate when I noticed it slow and eventually stop. Same now turning or drilling from the tailstock. I checked that the belt wasn't slipping and sure enough the motor stops.
Everything seems ok so my suspicions are the spindle bearings or the motor (motor, countershaft and front spindle bearing don't feel overly hot) although I have a feeling in my water that it's something to do with the spindle.
Sadly my mate who would've known what to do passed away last year and I don't know of anyone else over here (Jersey) to have a look so before I bu**er anything up do the collective have any ideas/suggestions on what to check?

Paul

What follows assumes that you have oiled all the bearings copiously, already, and that you have checked that all grubscrews, to lock pulleys, gears or the secondary belt tensioning lever, to their shafts, that should be tight, are.

Also that you have checked that the belts are tight when they are supposed to be, and free of oil? Your problem could just be belt slip.

A hot running bearing will likely pinpoint the source of your problem .

The motor belt tension should be applied just by the weight of the motor moving freely on its pivot.

F W I W, remove the belt from the motor pulley. Check how the motor runs.

If satisfactory, refit the belt and remove the secondary belt from the countershaft, and run the motor.

While the secondary belt is off the pulley, try to rotate the mandrel by hand.

If free, remove the change wheels, one at a time, and run before refitting, until you find what is causing the friction.

Eventually you should find the source, before undertaking a major strip down.

DON'T fix anything that ain't broke, in case you mess you it up needlessly. The worst sound in a workshop is the rattle of unseen and unidentified parts flying about before they roll out of sight and reach .

That is then followed by cries of despair and frustration. (I have too many T shirts for that!)

Howard

What follows assumes that you have oiled all the bearings copiously, already, and that you have checked that all grubscrews, to lock pulleys, gears or the secondary belt tensioning lever, to their shafts, that should be tight, are.

Also that you have checked that the belts are tight when they are supposed to be, and free of oil? Your problem could just be belt slip.

A hot running bearing will likely pinpoint the source of your problem .

Being a Super Seven, it has tapered bearing(s) on the mandrel has it not? Not overtightened the thrust bearing to remove any endfloat?

The motor belt tension should be applied just by the weight of the motor moving freely on its pivot.

F W I W, remove the belt from the motor pulley. Check how the motor runs.

If satisfactory, refit the belt and remove the secondary belt from the countershaft, and run the motor.

While the secondary belt is off the pulley, try to rotate the mandrel by hand.

If free, remove the change wheels, one at a time, and run before refitting, until you find what is causing the friction.

Eventually you should find the source, before undertaking a major strip down.

DON'T fix anything that ain't broke, in case you mess you it up needlessly. The worst sound in a workshop is the rattle of unseen and unidentified parts flying about before they roll out of sight and reach .

That is then followed by cries of despair and frustration. (I have too many T shirts for that!)

Howard

Hi

"The motor belt tension should be applied just by the weight of the motor moving freely on its pivot".

May I add to this that the motor then fixed securely to prevent it climbing up the belt and slipping when making intermittent or heavy cuts.

Eric

If 'any sort of cut' stops the motor, then its unlikely to be a bearing problem. From your brief description it sound like the motr is not producing the power it should (or used to do).

What has caused the loss of power depends a lot on what type of motor it is and/or how its wired up. Induction motors are usually extremely reliable but I suppose a 'run' capacitor might be faulty.

Have you got full mains voltage at the motor terminals? if for any reason the mains wiring was higher resistance than it should be (pretty unlikely) then the voltage would drop under load and that would reduce the output power.

Please can you provide more info of the whole setup and the motor details as I am sure someone will have an answer.

Ian P

If applying end pressure (from the tailstock eg) causes seizure, I would check that the spindle taper is not being forced back into the tapered bronze bush in the headstock.

All the above from other posters are of course valid courses of action; this is just where I would look first.

Thanks Gents,

Nothing has been changed/adjusted on the motor front, the tumbler gears are not in mesh and the countershaft and spindle have been lubricated as per usual.

Seems odd that the motor slows on axial as well as radial turning so maybe this points to the motor? It hasn't had a lot of use and only 17 years old.

Motor voltage? Hadn't thought of that, I'll check the output of the contactor from the switch box but I've never come across this before.

I'm not really sure just how free the spindle should be, I've seen it written that it should be 'free to turn' but also that it should be 'just able to be turned by hand', both cases with the countershaft belt loose of course, mine is pretty tight but not what you would call stiff.

Thanks in advance,

Paul

I have had similar with my S7. it turned out it was the no volt release switch which had the contacts burned, so do check that before you take things apart. Niko.

Yet another NVR switch bites the dust, it does appear the contacts are only rated for control circuit currents, not motor loads when switching ON or OFF.

Emgee

Thanks Niko. I thought it was just me but the NVR assy does seem to be buzzing a bit louder than usual now you mention it.

Paul

Well I've checked the relay which seems that the contacts are clean and voltage in/out is the same 239V.

I think I'll put a DTI against the spindle register and push with the tailstock.

Could a problem with the rear thrust bearings cause the spindle to push back and tighten up whilst turning?

Paul

Paul, yes, it could. Give the front of the chuck a tap with a rubber mallet, if it's hard to turn afterwards your thrust bearings need attention. Dave

I had the same problem with my 254 after not using it for a long time, it was the centrifugal switch on the motor not operating, so it was stuck in start mode, hence no torque

Had the same on an old ML7 (white metal bearing cups) with 1/3hp motor about 21yrs ago, no relays just the forward/off/reverse switch replaced twice in 8 years.

Fitted a Brooke Crompton 1hp motor though a 3/4hp more than adequate, job done and transformed it in to something useful.

Yes, very much so. On the Super 7 you have the tapered bronze front bearing. if the rear bearings/thrust bearings are not set up very carefully, the tapered spindle will bear down into the tapered bronze bearing and start to grip like a Morse taper drill shank in a tapered drill press spindle.

You need to look at the lathe manual on setting up and adjusting the bearings, and I'm sure there are multiple threads of good advice on the same on this site.

Before you make adjustments, which should be minimal, mark the position of the split collar and the left adjusting ring for rear bearings. It gives you more control over what you are doing and you can easily return to the original setting. Niko.

Before you strip or adjust anything, I think you need to check that the centrifugal switch in the motor is operating correctly. As Alan Lloyd stated, having the start winding in circuit all the time could well be the cause of your problem. Easily checked by running the motor without it driving anything and see if the switch can be heard when the motor starts or stops.

Thanks Gents, Looks like I'll be busy today then! The centrifugal switch can be heard clearly as the motor stops so I think that's OK but I might wire the motor directly to the mains bypassing the nvr and reversing switch just to check before I start ripping the headstock apart,

Paul

It is likely a start or run capacitor problem. If it has start windings it may have both.

As it exceeds the start winding speed (switch turns it off), I would suspect a run capacitor failure, as Ian Phillips early in the thread. But equally, the start winding (which is high torque at low speed) should re-energise as the motor is slowed and carry the speed back up until it is switched off once more.

Start windings will soon overheat if running continuously, so be aware that continued operation in such a state may well end in a winding failure.

I've browsed this forum for a while but this made me have to sign up.

Many years ago whilst a young apprentice (electrical) i was walking past the machine shop and saw one of the fitters at the myford, i went over for a chat as one does.

As I approached he said scratching his head" ok Mark, tell me what i am doing wrong".

He switched on the lathe which spun up but as he tried to put on a cut the spindle stopped, you could still hear the motor running.

"Here" i said with a smirk and engaged the drive peg (the one to allows the back gear to drive ) , I think it was something on the lines of "bugger off you clever little shite" with a red face.

Hope yours isn't the same problem, ok its an easy fix but the embarrassment makes a motor rewind preferable.

Also ours had myfords excuse for a clutch, he would turn the spindle disengaged but then slip with a light load.

You should be able to open guards and see what pulleys are running and whats not and whether the motor is stalling.