Lathe Motor running Lumpy :-)

Hi All

The motor on my 5 year old Chester crusader started to run rough, enough to affect the finish on the work... So I mauled it off and had a look. It's a HP (1.5KW) capacitor start / capacitor run 4 pole heavy lump of cast iron.
(I have turned the bulk of the bits for a 6" Traction Engine on it, so it has done some reasonably hard work; no complaints about it's age"

The 35 uf Run capacitor had clearly had a Vesuvius moment and I got new replacements for both that and the 200uf start one... Same Voltage and duty motor caps were replaced. At the same time I replaced both bearings with respectable ones as the rear was was shedding grease from the seals.

Inspecting the windings there were no brown and crispy bits, and no smell of "magic smoke" , it was clean inside so I re-assembled it and refitted it.

Sadly it still is rough and noisy, with or without the belts on. So I either made a mistake fitting the caps (don't see how) or the windings are shot....

Anything else I should check before either fitting a new 1 phase job or going the whole inverter and 3 phase route? (150/450 quid; lots more effort to integrate the 3 phase properly and there is work setup in the chuck)

What else do I check on the existing one? Thanks Mark

Looked up Chester spec,its expecting a lot to drive a 6 inch c/h lathe,with a speed range of 60 to 1800 rpm wiith a 1.5 kw (2hp motor) If a new motor is required I would think 3 hp 3 phase is a minimum, Older lathes of this type used to have smaller motors as they had a lot lower top speeds its the 1800 rpm that kills a 1.5 hp motor plus the extra load when the feed shaft is engaged. Though I dont know why the motor is lumpy I would have expected a total failure,I have owned 3 Colchester students /masters (similar size) of early and late types and as spindle speeds increased over the years ,so motor HP has increased.

I feel your pain Mark!

My Crusader got through 5 or 6 capacitors before I bit the bullet and got a VFD set up. I can honestly say it transformed the lathe!

The VFD unit is 2hp, but it feels like 3 times what it was before.

Jim

Can you borrow a current clamp meter? The running current might be excessive, which might indicate a winding fault (shorted turn). If so the fault is terminal (excuse the pun). I'd be suspicious at this point that the "Vesuvius" complex you describe is the effect rather than the cause.

One might expect to have a smell of cookery to accompany the diagnosis, but maybe not (yet!)

Are you on a RCD? Might be prudent - if the windings flash to earth it would be better switched off sooner rather than later. Just check the plug top earth pin makes a good contact to building earth (guess what I got caught by!)

I' m assuming being single phase it is not variable speed? If it is there's another can o' worms.

Let us know how you get on.

Simons clamp meter will tell you the truth.

Grease normally gets forced out by heat, which is mostly too much current. I had a 3/4hp old general electric that started tripping the thermal cut out after 20 mins, the casing was at 60C - clamp meter said 10A running instead of 6A ish. No smell, no funny coloured windings, I have no doubt the smoke would have come out with out the thermal trip..

Have you tried spinning the motor without power on, just in case the roughness has a mechanical source rather than electrical one?

Check the function and condition of the centrifugal switch if fitted

Thanks Everybody, I've tried most of what everybody suggested...

Nigel: the cheat they make is that there are 2 belt positions, I always use the lower speed one... It's a real pain to change it... You have to remove the chip guard, minimum 45 mins awkward work (maybe simpler if not back to a wall)

Old Mart: Mechanically it's fine, I put new quality bearings in and if I run it up to speed with my cordless drill it's silent and smooth on the run down...

Simon: I think the centrifugal switch is ok, you can hear it move when the motor runs down, and all seemed free and clean when it was dismantled.

I've had it in pieces 3 more times, and it always has a vibration when running, exactly how much varies with the assembly of the case, machining was not the best.... It would be ok on a concrete mixer, but now too rough for my lathe.

I've lost a couple more weeks (and 40 quid in bearings and capacitors) now, so it will be a new 3 phase motor and inverter... Just need to decide what brand of motor - AMTEC, TEC, TECO and Brooks Crompton seem in vogue at this size... Any opinions welcome

Thanks Mark

Or you could take it to the motor rewinders. Not sure how much it would cost you. When contracting i had a guy near Leeds who charged about a 1/3 of the price of a new motor. Always made a good job too. It's an art of sorts.

Quite a few times we had motors giving the same symptoms as yours. No smell but lumpy in operation. Was usually one winding that had gone low resistance.

Steve.

Spend the money on a three phase conversion and a VSD, I know it looks expensive, but it transforms the machine and you'll only wonder why you didn't do it long since.

Goo d luck, do please keep us posted

Rgds Simon

I have a Chester Craftsman lathe, speeds 50 to 1200 6" centre Ht and fitted with a 1.5 hp motor.

Do the team consider that this might be underpowered ?, and yes, it is a pain changing the belt from one pulley to the other, but I,ve got used to it.

Forgot to add, 5 years seems a very short life for a motor like that.

Since the motor seems to be smooth when run up with an external power source, could it be that the motor is OK, but that something else is the cause?

Belts? A failing belt can cause rough running at the mandrel. Some cheap belts have poorly made joins.

A loose / worn pulley? Worn Key/keyway,

Bearings in the Headstock?

Is the chuck accurately aligned? Clean, undamaged thread and / or registers?

Keep us posted, please

Howard

Thanks Larry and Howard.

There is still vibration when running the motor on the bench, wired to a 13A plug...

I've "run" the lathe up to speed using a cordless drill (needs must) on the lay shaft and it's all feels as smooth as normal, I've had the top off the headstock and nothing was loose or rattled.... The keys are retained with csk screws and checked all of those....

There is no obvious deflection on the headstock with a DTI.... so think it's ok, I snugged up the headstock bearings a touch after 6 months and have had no hassles with them since.

Belts are Dunlop and pretty new, I bought 3 and used the best fitting pair.

I am as sure as I can be that it's a motor winding... Using a clamp multi meter I got no useful information.... It draws maybe 1 amp unloaded but I have nothing to compare it with; it's rated at 8.1A on the plate but that would be fully loaded... The current rises slowly as the motor gets warmer but only by 20%

I am going for 3 phase and an Inverter as it will be a better solution long term, not retired yet so now is a better time to spend the money than in a couple more years... or so I tell the domestic management

Many thankS
Mark

I'm not 100% sure what's going on here, but my reaction to 1amp current running light and a rated FLC of 8A is that the motor is definitely poorly, and maybe lost a few windings. I'd expect the off load running current to be round about half or maybe a third of the full load current, not an eighth.

The reduction in input power at light load with a squirrel cage induction motor - particularly a single phase variant - comes largely from having a lousy power factor at low load. The power factor is quite tricky to measure and it's generally more meaningful just to measure the effective current and see if it makes sense.

Which - for me - this doesn't. It's sicky poorly.

As an aside, the clamp meter knows nothing about power factor, it just measures the magnitude of the effective current, which is the vector sum of the real and reactive supply currents. At low load much of the measured current is at a low power factor (reactive current) so it represents a low input power even though the clamp - normally - displays a significant current. You can't just measure the line current and multiply it by the voltage (line to neutral in this case for a single phase motor) and call it input watts.

I just ran a moving coil clamp test on a low use 1/2HP Brooke motor plated for 4A that I kept as a spare.

No load, 6A start peak 3.5 A running, so yes you did get useful information from your clamp, that motor is dead.