Thread: Lathe stops when it's not supposed to

Bodgy,

My lathe doesn't spin backwards so I have ruled out the capacitor. I have looked at many of the threads here and actually came across one of yours which helps a little. I tried the talcum powder trick on the belt. It seems to have helped, but the lathe will still not start at times and if I stop the lathe while it's in a high speed say 1500 + , then it will not start unless I give it a spin. Makes me think it could well be the belt, although it doesn't look in bad shape and I can't see any slippage when I run the lathe without the sheet metal cover.

There are no instructions though on how to take the belt of the pulleys. Do you use circlip pliers, removes spring, then allen key....

The torque problem isn't as noticeable with timber other than redgum, but this start up problem has been consuming more of my time now.

Tiger

I didn't make myself clear, sorry. My spinning backwards probelm is caused by corrosion in the windings, not the capacitor, due to a very damp shed and neglect (since fixed). I mentioned the search on backward spin cause it also covers the capacitor problem.

The not starting problem is the capacitor. As I understand it the cap stores up power, jumps up the amps/wattage or whatever and then squirts it out at start-up when needed to overcome the inertia. NB This is from someone who just scraped Physics at school.

I'm a little unclear too. When you say it fails to start, does this mean the motor dont go around and just sort of hums threateningly, or do you mean the motor spins but not the spindle?

I the motor turns OK at start up and the problem is with the spindle then ignore the above, sorry. It must be the belt or pulleys. Can't help as my Chinese cheapo aint as flash as yours, its a manual change speed by moving the belt to different pulleys. One screw is all that locks the drive shaft.

Not familiar with this lathe, but if it has a reeves drive then try to always put it on the slowest speed before you turn it off. The motor has quite a time trying to start when on a higher speed.

Tiger
The starting problem could well be the capacitor , or the starting load is just too great for the motor to overcome
This could be any number of thinds from belt alignment ( unlikely ) to a bearing needing re packing ( again I think unlikely ) to a bush needing oiling or lubricating
This may be adding to your promlem, Does the lathe have greese nipples or oil points and when was the last time you did a lub job on the lathe , including the tailstock


The trouble with life is there's no background music.



Ashore

Originally Posted by Bodgy

.... As I understand it the cap stores up power, jumps up the amps/wattage or whatever and then squirts it out at start-up when needed to overcome the inertia. NB This is from someone who just scraped Physics at school......

Not really....some AC theory required here... there is a second winding that is physically placed out of phase with the first & the capacitor changes the phase angle of the incoming AC. As well as helping start the motor it ensures that the motor always runs the correct way.

The belt is not too tight is it?

Originally Posted by Cliff Rogers

Not really....some AC theory required here... there is a second winding that is physically placed out of phase with the first & the capacitor changes the phase angle of the incoming AC. As well as helping start the motor it ensures that the motor always runs the correct way.

The belt is not too tight is it?

Cliff, can you be a bit more explicit? The Capacitor must store power somehow, or else how does it give you that huge belt when you touch the contacts when the powers off to the machine? Sorry, don't understand.

Sorry Tiger, hijack underway.

Long story, involves understanding of AC & DC circuit theroy.

The Cap will store a DC Voltage (that's what bites you) but passes AC Current 90° (approx) out of phase (leading).

It won't store enough to kick start a motor.
If it relied on that & you didn't use your motor for a while, when you went to use it, your cap would be flat.

The tricky bugas that thought this up rely on the change of phase angle caused by the cap & the start winding being placed out of phase with the run winding to make it always start & run in the same direction.
Only applies to AC motors.

The rest is beyond the scope of my typing I'm afraid, if you need to know more than that, you'll have to google it.

Thanks Cliff, thats enough!

Originally Posted by Tiger

Cliff and Apricot,

Tried to turn it in reverse, the mere touch is enough to get it to turn and it turns in the right direction so I guess we could rule out electrical problems?

Really in a quandary here, Help!

I'm no expert. But I do know there are many types of motors out there.

You can get single speed non-reversing circuits. Centrifugal starts etc.

So, IMO, just because its not going in reverse doesn't mean its not the capacitor.

The most frequent problem I've come accross in all the motors I've fixed is the capacitor. From mixmasters to washing machines. So, I'm still betting on it being a capacitor problem. I'd try and replace the capacitor first to at least rule that out.

Goodluck.

I've never ownesd a lathe , but a bit of common sense here. If its pretty new take it back get your money and buy another (at least GMC gives you a 2yr waranty). If its new dont even try to fix it get your $ back ...

Like someone else wrote if its in too high a gear like trying to start a car off the mark up hill in 5th.

GO GMC!!!

Assuming you have eliminated the obvious possibilities of the drive chain, loose pulley, slipping belt and if the syptom is that the motor humms but doesn't turn when you switch on and that flicking the shaft by hand gets it going then its almost cetainly a problem with the start winding. Assuming you have a single phase motor i.e a standard 3 pin 10 amp plug - most of us do - then you will have a motor with a start winding and a running winding. The problem is most likely that the start winding is either fried, or the start winding capacitor is on the fritz ( the most common diagnosis - it is changeable and usually sits outside the motor housing) or the mechanically operated internal centrifugal switch is not functioning. This switch sits around the motor shaft with spring loaded weights and clicks in and engages the start winding when the motor slows right down or stops and helps to get the motor started and clicks out and transfers the work to the main motor winding when at speed. By flick starting by hand you are in effect doing what the start winding does. If the motors centrigfugal switch clicks in when you put a heavy load on the motor and then clicks out when you remove the load then you are at least blessed with an underpowered setup or at worst a flakey motor.
For the technically minded 3 phase motors have no start winding and no centrifugal switch so are inherently simpler in design and usually therefore horse for horse a bit cheaper and more efficient. Three phase is generally desirable in terms of efficiency and cost of gear but bear in mind you have a greater potential electrical hazard because in polyphase installations the phase to phase voltage is about 415 whereas a single phase environment is a 230 to 240 volt maximum. A 3 phase belt is frequently lethal which is not to suggest a 240 volt one is pleasant either.
In summary if you have eliminated the mechanical causes it is lilely to be electrical.
Mike Jefferys

Isn't the easy way to determine if its electrical or not, to just isolate the motor temporarily......I mean, just take the belt off, start the motor. Does it start properly without it connected to the spindle ? .....yes ? ....well, is it providing any torque ? To check this I'd just put on a thick glove, like a welding glove or the like, and just cup the motors shaft or pully in my hand. Tightening my grip to see if I can stop the motor in my hand. If it wavers, or stops. well, its definetly electrical. right ? Shouldn't be able to do that with a healthy motor.

First of all a huge thanks for your efforts in trying to help me diagnose the problems with my lathe. Yesterday, I'd had enough and so I took the capacitor cover off the motor. Had a close look at it and tested it with the multimeter, no reading. Rang the place where I bought it from, they said it's probably the capacitor, we don't have any in stock , they cost around $24, if you pay freight, that's another $12 and you can have it tomorrow, otherwise 2 weeks. On the capacitor, were the specifications. I rang Middy's, they don't carry these parts. Went to Actrol (air conditioning parts) and they had 1 left at $16 (and it was a much better version imported from Italy) but it was a different design to the chinese job that was in mine. Asked the salesmen there to test his capacitor and that didn't register a reading either :confused:. It took a little bit of work and modification but I was able to attach it to the lathe. Then I tested it, it worked, stopped it and re-tested again, must have stopped and started it 20 times and it worked every time. The lathe seemed to even run better with the new capacitor. Spurred on by this, I then had a look at the tailstock which had been bugging me. It seems that the nut underneath the ways has to be tightened in the right spot before it will hold efficiently. Managed to fix that too.

Then the drive dog. With a file, I carefully sharpened each of the 4 spurs, then tested it on redgum. It was better but I wasn't satisfied. I then sharpened some more and the spurs were very sharp. Tested the redgum and it stuck, even a fairly big chunk (about 400 long and 80 in diameter), no lathe stopping now. The roughing gouge is still a problem but I have convinced that the steel is not as good as the other lathe tools and that is why it is causing problems but I'm happy with the lathe for the moment.

Originally Posted by Tiger

...tested it with the multimeter, no reading....to test his capacitor and that didn't register a reading either :confused:. ...

Beauty.
Don't pay too much attention to the reading you get from a multimeter on a cap, particularly if it is a digital meter on the ohms range.
You will only see a steady reading if it is shorted out.
If you use a moving coil meter on the ohms range, you should see the needle flick up & drop back & then when you reverse the leads, it will do it again.
You can get fancy meters for testing caps but the best & cheapest way is to replace it with a known good one.

OK, make the chips fly.