Motor trouble.

[dobbslc]

Recently the motor on my lathe has been playing up when I start it from cold. It's worse on the highest speed (twin belt drive), once it's warmed up a bit it runs perfectly.
The centrifugal switch keeps clicking in and out and the speed goes up and down. It's not getting up to full speed then the switch cuts in again and it keeps doing this until I switch it off.
Would a dodgy start cap cause this? The motor and switch look like new inside no burning etc. The caps look ok but I don't have a proper capacitor tester.

Any ideas?

 

[The_Yellow_Ardvark]

@dobbslc
Do you have a Multi Metter/
If so a simple test.
Pop the Cap out of circuit, discharge it.
Put the meter across the terminals, set the Highest resistance reading.
Step down until you get a meter reading.
It should slowly decrease.

It will tell you simply if the capacitor is open or short circuit.
Are the cap cans straight, no budging?

 

[WorkshopChris]

Does it do the same with the belts off?

 

[Seadog]

Once the centrifugal switch has switched on the run-up the capacitor no longer has any effect so, no, I don't think it's the capacitor. It definitely sounds mechanical; old grease in the bearings perhaps or somewhere else in the drive chain. As Chris has asked, 'does it do the same with the belts off?'

 

[arther dailey]

switch may be sticking on shaft, either way dont use it like this you will burn out start windings, strip motor clean the electrical points on the oc switch, wipe on wipe of grease on shaft where switch slides,check /replace bearings, obviously check windings to earth etc, re assemble.
you have already been advised how to test caps,other method is charge with megger tester,then discharge(goggles) with a screw driver blade accross conections, you should get a fat noisy crack of a spark,if not its fubar.Arther

 

[dobbslc]

TYA the caps look fine and it runs well once it's had a couple of attempts to start it.
I'm not sure a normal meter will pick anything up as its not completely kaput! but I'll have a test later.

WorkshopChris it seems to only do it on the highest speed setting, everything turns freely no binding or anything. That's why I thought it could be the cap going soft, it seems to have enough punch to start on the slower speeds but not the higher load.

Edit:

Arther, The switch is like new it moves nicely so I don't think it's that. Everything is really clean inside which was a surprise as the outside is covered in swarf !
PDG, Your probably right it's getting up to speed then slowing down so the switch cuts in again, yes it has start and run caps so I'll find some new ones.
One is 18uf the other 100uf, what is the start and what is the run cap?
Cheers lads.

 

[arther dailey]

ok, the point is if its not getting up to speed the switch will flick in/out in/out and you will burn the motor out, either the machine being run is maybe tight when cold, or there is a fault on the mtr.Arther

 

[WorkshopChris]

Does the motor vibrate on the higher speed Or is it on rubber mounts, am wondering if its getting a intermittent supply on the higher speed maybe a broken wire?
Causing the motor to momentary slow enough for the switch to cut in again.

 

[dobbslc]

It's solid mounted there is some vibration off the pulley but it's always been like that.
I think it could be suffering from "cold compressor syndrome" As like I said once it's been tried a few times it work fine.
Think I'll get the Megger out the van and have a crack testing the caps!!!

 

[arther dailey]

stick a fan heater up to lathe mechs with cover off for half an hour, if it runs fine you know whats the problem.

 

[garethp]

ok, the point is if its not getting up to speed the switch will flick in/out in/out and you will burn the motor out, either the machine being run is maybe tight when cold, or there is a fault on the mtr.Arther

My lathe does exactly the same as my workshop isn't heated, clutch disengaged motor spins up, engage clutch and speed drops / start switch rapidly clicks and out. I run it a lower speed until it warms up.

 

[arther dailey]

thinking back to just after the dinasours when I was a lad, the engineer used to clock in, walk up to lathe and turn it on and leave it running slow then go to canteen for tea.although that was three phase similar thing I guess, I have a large single phase pan mixer , I do the same just to warm up the gear box.Arther

 

[dobbslc]

My lathe does exactly the same as my workshop isn't heated, clutch disengaged motor spins up, engage clutch and speed drops / start switch rapidly clicks and out. I run it a lower speed until it warms up.

I don't have the luxury of a clutch
And to change the speed I have to **** around swapping belts about!
I do need to change the headstock oil though so maybe I'll get some of that blue stuff I saw @doubleboost putting in his lathe .

 

[garethp]

I don't have the luxury of a clutch
And to change the speed I have to **** around swapping belts about!
I do need to change the headstock oil though so maybe I'll get some of that blue stuff I saw @doubleboost putting in his lathe .

Sounds like oil is the way to go then

Kinda related, I had a Mx5 years ago and the box on that was really notchy and stiff when cold, apparently it was a common problem and I was told changing the box oil to fully synthetic would cure it and it did. Redline oil was recommended at the time, probably other brands are just as good.

 

[Rig Pig]

Is it an undersized motor or a 3ph to single conversation?

 

[normspanners]

really notchy and stiff when cold

that sounds like my knees !!

 

[normspanners]

Thick old oil /grease is my guess also old belts can be stiffer when cold, especially none cogged belts it all adds up.

 

[arther dailey]

iveco daily gearboxs are the same, like stirring cold tar if wrong oil is in,change to synthetic and sweet as a nut.

 

[colnerov]

that sounds like my knees !!

Yes, mine as well, too many years crawling around on concrete floors.

Colin

 

[dobbslc]

This seems to be what's in my headstock!

As it says "oil" on the filler plug I'll assume this is not right!
But what do I use?
There's too much confusing info around and Chester themselves have told me look at the manual, this is after I've told them the manual doesn't say what to use!


Here's a picture of what I assume is the FILL plug on the top right by the cable, do I fill it until oil starts coming out like a car diff? Also what's the brass oil pressure sensor looking thing in the middle below the chuck?
There's a drain plug at the bottom rear of the headstock but I'm not sure what will come out!