problem with my lathe single phase motor

[kev]

Been having the odd hickup with the motor on my myford lathe.

Its about 2 years old but gets a LOT of use and just lately 2 or 3 times a day it does not start just sits and hums, all I do is switch it off, push the pulley an inch or two and it will start straight away.

Any clues as to whats going on? Bit worried as I use the lathe every day and apart from the cost of a new motor the down time would be bad news and I would rather plan for it than the machine pack up.

[Bertie_Bassett]

first thing i always look at with single phase motors is the capacitors, they only have a limited lifespan and can often result in a burnt out motor if they are not changed.

if they are on their way out and then they generally don't have a lot of umph to kick the motor over, a slightly tight spot would be enough to stop things from starting up.

could also be the centrifugal switch though, if it get stuck in the run position then it wont switch the start cap in and the motor will just hum, by moving it a bit it might be resetting things and letting it start up.

try removing the belt and testing the motor on its own some more,might give an indication if its a tight spot on the machine stopping things and you should be able to hear the centrifugal switch click in and out.

tbh if i have any doubts i normally just slap in some new capacitors, nine times out of ten that cures things

[Alyn Foundry]

Hi Kev.

One of two things, probably.

The motor " start " capacitor giving up or more likely the centrifugal switch contacts aren't doing what they should.

Based on the description it might be that the sliding portion of the switch isn't coming back far enough to close the contacts. If you're feeling confident it'll mean removing the motor end plates to find the switch.

Don't forget to isolate the electricity supply! before you start.

Not knowing what or who's motor is fitted it'll be a case of " pot luck " as to which end the switch is fitted.

Regarding the start capacitor they are usually fitted under a case that's screwed to the motor body, you might also have two " bumps " depending on whether it's a cap start cap run motor. But they usually fail
" catastrophically " with a loud bang!

I'd be inclined to check the centrifugal switch first.

Cheers Graham.

[kev]

thanks guys, confirmed my thoughts

i was thinking either the capacitor or the internal weighs ie centrifugal switch needs a clean up. Its easiest to whip cover off and change caps first as getting the motor out involves unbolting the whole lathe etc

So next weekend will take a peak and order some caps to try

[Bertie_Bassett]

forgot to mention a couple of things to watch out for whilst your using the machine. rather obvious but worth mentioning.

don't let the  motor 'hum' for too long, it will only get hot and the capacitors may blow.

additionally if the motor sounds odd whilst running, stop things as soon as you can, as again the capacitor may blow.


ohh and dont breath in blown capacitor fumes, the old ones gave off nasty gases and i doubt the new ones are any better for your health.

[kev]

Many thanks for that, only done it once in the last 4 hours and switched of straight away so hopefully it will limp along till I can get a down day to look at it and see what the cap looks like

[Admiral_dk]

The "fumes" are concentrated sulfuric (or chloric) acid and can destroy your lungs if inhaled ..!!!!!

Clean everything afterwards if it happens for the same reason - it will destroy metal parts.

If you happen to be around when it happens - hold your breath, switch off the equipment and open the nearest window. Here you can grab another breath and then leave the room and the door open to get a draught of air going through.

Good luck solving the problem and best wishes

Per

[Art K]

Kev,
Our lathe at work did the same thing. The first time it was about $150 to have a guy come in and fix it. after that we(I) knew what to do. Under the cooling fan cover was a pair of contacts like points, they were sticking together. Cleaned them up and it was fine. I think as was mentioned earlier that they are part of the starting circuit. Don't know about your lathe but ours is a pain in the back side to remove and reinstall the cover screws.
Art