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Lathe won’t spin up to speed

G

Gevan Marrs

Joined
Nov 18, 2024
Messages
15
Likes
4
Location
Puyallup Washington
IMG_9754.jpegCraftsman 2hp variable speed lathe. Has worked fine for months, but suddenly stalls and won’t turn. Formerly I could turn the spindle by hand- now it seems bound up and I can just turn it with the chuck wrench. Tore it completely apart. Rear bearing spins free and easy. When the rotor is removed from the magnetic housing, it spins free and clear, easily. But when placed back in the housing and carefully aligned and tightened, still binding up. I’m mystified. Help?
(And thanks, I’m not seeking opinions about whether this is a good lathe. Just helpful comments, please. TIA)
 
Some older electric motors have a felt seal near the bearing that requires a couple to a few drops of oil to keep the bearing lubricated. I doubt that what I'm letting you know about is your problem, but I do hope that you find a quick resolution to your issue.
 
Looking at the manual it appears to be a direct drive (no belts) lathe with a brush type motor. Is there a gear reduction between the motor and the spindle? I would assume something in that area is bound up.
 
Yes, it is direct drive with no belt. Yes there is a gear reducer. I pull the shaft out completely. The gear reducer is as free as a bird so no biting on either end of the bearings only when I insert it back in the magnetic case.
 
I may have to go that route. After playing with it all day, I am convinced the rotor coil is rubbing on the stator magnets. It can be turned by hand, but is very "sticky". Yet there is no play in the bearings to allow it to have shifted... note the rub marks on the left end of the rotor coils. Thanks for the suggestion.IMG_5742.jpeg
 
Richard Elliott said:
Are the magnets still Tightly glued inside the motor housing?
That glue can fail due to heat and/or age.
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Beat me to it. I used to see that a lot on Kohler starter motors when I was in the OPE business - starter would get hot (due to engine overheating/ lack of maintenance) and all kinds of magnets could come loose from their original epoxy glue - not just starters either, but flywheel magnets (for alternators) were also a common issue (more often on twin opposed engines which were notorious for being tucked in to small engine compartments and never getting the cooling systems maintained) Also even a bit of impact on the housing of the motor can cause magnets to crack or separate, so when seeing that sort of rubbing given the magnets in the housing, one of the first things I'd do is a close inspection of the magnets - Another possibility is the end cap (which also holds the bearing for the rotor shaft) could have shifted or torqued a little bit allowing the rotor to shift slight off center of where it should be (were any of the through bolts even slightly loose?) Just a few things to think on, perhaps but if its out of your depth a motor repair shop (or starter generator shop, etc) may be of some help to resolve it...
 
Can you feel whether the resistance is smooth or grinding? I wonder if the coils are shorted. It would have the effect of having 2hp of braking force. One test is to try to rotate with the wires disconnected.

If it is mechanical I would check whether each component is aligned, particularly the gearbox.

Also I just noticed that it's a brushed motor, I would make sure the brushes aren't cooked and each segment of the armature is clean and not shorting to the neighboring contact point.
 
I think these last two comments are on the right track. I was drilling out the center of a very large block of dense, wet plum wood and the motor was clearly working hard, and getting warm. When the output shaft is turned with the chuck nut and a wrench, (power disconnected, brushes removed) the resistance “pulses”, like skipping from one coil section to the next. Without the magnet stator in place, both the inboard and outboard bearings turn freely and I cannot detect any play. I am confident that bearings, brushes and gear reduction are all ok. As for the magnets, they seem to be glued tightly, but I suppose may have shifted with heating. They do seem to be wear marks of the rotor and a bit of metal filings on the magnets, so something is physically rubbing. I guess it’s off to the repair shop. Thanks to everyone here for assistance!
 
Michael Brown said:
Can you feel whether the resistance is smooth or grinding? I wonder if the coils are shorted. It would have the effect of having 2hp of braking force. One test is to try to rotate with the wires disconnected.

If it is mechanical I would check whether each component is aligned, particularly the gearbox.

Also I just noticed that it's a brushed motor, I would make sure the brushes aren't cooked and each segment of the armature is clean and not shorting to the neighboring contact point.
Click to expand...
The resistance is not “scraping”, but “pulses”, like magnetic from sector to sector. There were some metal filings stuck to the magnets. Could these be magnetically connecting to and dragging on the rotor? I tried to remove them all, but challenging.
 
The carbon brushes are not shown in the picture but they should be checked. If the brushes are worn down such that they only make intermittent contact with the commutator bars then that would explain why the motor does not get up to speed and appears to pulsate rather the scrap. The planetary gear box would probably make it seem like the motor is bound up when trying to turn it manually at the output end.
 
Don Wattenhofer said:
The carbon brushes are not shown in the picture but they should be checked. If the brushes are worn down such that they only make intermittent contact with the commutator bars then that would explain why the motor does not get up to speed and appears to pulsate rather the scrap. The planetary gear box would probably make it seem like the motor is bound up when trying to turn it manually at the output end.
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The brushes had been replaced a couple months ago and look good to my eye. I know how hard the gear reduction turned before - stiff but quite do-able. Now I can barely turn it by hand - very different.
 
Gevan Marrs said:
The resistance is not “scraping”, but “pulses”, like magnetic from sector to sector. There were some metal filings stuck to the magnets. Could these be magnetically connecting to and dragging on the rotor? I tried to remove them all, but challenging.
Click to expand...
Does the pulse still occur when the brushes are removed from contact to the stators? If the system turns freely once the coils are not electricity engaged I would inspect the speed control. Another way to inspect this is to compare forward rotations to reverse. They should be slightly different in feel when trying to rotate against the direction bias of the motor. Ie when the motor is set to forward, it should be harder to rotate it backwards.
 
Gevan Marrs said:
I think these last two comments are on the right track. I was drilling out the center of a very large block of dense, wet plum wood and the motor was clearly working hard, and getting warm. When the output shaft is turned with the chuck nut and a wrench, (power disconnected, brushes removed) the resistance “pulses”, like skipping from one coil section to the next. Without the magnet stator in place, both the inboard and outboard bearings turn freely and I cannot detect any play. I am confident that bearings, brushes and gear reduction are all ok. As for the magnets, they seem to be glued tightly, but I suppose may have shifted with heating. They do seem to be wear marks of the rotor and a bit of metal filings on the magnets, so something is physically rubbing. I guess it’s off to the repair shop. Thanks to everyone here for assistance!
Click to expand...
I had to read this one a few times and I now want to ask: are all the insulating inserts and spacers still where they belong? It sounds like the induction from the magnetic fields are activating windings at intervals but not constantly. I would check the end of the armature on the edge of the commutators to make sure they are not shorting together, for example on the bearing race. By design the surface is machinable to remove contamination and corrosion buildup from heat. There needs to be clean and clear lines between the contacts of the commutator where the insulation strips are located.

On a further note, I would check the windings for shorting. Getting the motor hot enough can liquify the enamel of the magnet wire creating shorts across the winding. Easy enough to check with a DMM
 
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Michael Brown said:
On a further note, I would check the windings for shorting. Getting the motor hot enough can liquify the enamel of the magnet wire creating shorts across the winding. Easy enough to check with a DMM
Click to expand...
When the windings in a DC motor armature are shorted the commutator bars will show burn marks on the edges that are caused by the arcing that happens when the brush passes between the bars. The photo of the armature does not show any sign that arcing has occurred.
 
Don Wattenhofer said:
When the windings in a DC motor armature are shorted the commutator bars will show burn marks on the edges that are caused by the arcing that happens when the brush passes between the bars. The photo of the armature does not show any sign that arcing has occurred.
Click to expand...
I typically don't work with this large of brush motors, there is a lot of surface that is blurry and shadowed so I can't see arcing burns (I can trust you are right). The com overall is very discolored, so I guess I would still turn down the surface to up the conductive properties and then perhaps also re-brake-in the brushes.
 
Just for closure on those that gave help. I took the motor and controller to motor repair shop. Without disassembly they tested the motor and say it shorts out. Guessed it needed re-winding at an out-of-state facility, couple hundred bucks estimate. Also said the controller board was defective, putting out AC instead of DC current. No estimate possible as to whether it could be repaired or replaced... All this for a lathe I purchased for just $200, so seemed like a poor investment. I ended up looking at, and eventually buying, a new Laguna 1216. I'm very happy with it (except for the cost, of course....). I figure it should have good resale value. Now I have a vintage monster lathe available to anyone who could benefit / rebuild / part out, etc.
 
Gevan Marrs said:
Just for closure on those that gave help. I took the motor and controller to motor repair shop. Without disassembly they tested the motor and say it shorts out. Guessed it needed re-winding at an out-of-state facility, couple hundred bucks estimate. Also said the controller board was defective, putting out AC instead of DC current. No estimate possible as to whether it could be repaired or replaced... All this for a lathe I purchased for just $200, so seemed like a poor investment. I ended up looking at, and eventually buying, a new Laguna 1216. I'm very happy with it (except for the cost, of course....). I figure it should have good resale value. Now I have a vintage monster lathe available to anyone who could benefit / rebuild / part out, etc.
Click to expand...
Some turners love to play with, repair, fix up, recondition lathes, and some of us just want to turn wood. Find one of the former to re-home your old lathe, and be content you are the latter.
 
You should have no problem finding someone to give it love, though it may take a little time. Get the 3-4 woodturning clubs in your area to put a mention in their newsletter. Also, there's a web site devoted to people who like reconditioning vintage woodworking tools. I can't recall the name, but maybe someone will pipe up.

(The Puyallup Farmers Market is my all time favorite. Too bad my daughter moved away)
 
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