how hot is the motor supposed to get?

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Forum topic by fumehappy posted 04-25-2013 04:04 AM 3250 views 0 times favorited 33 replies Add to Favorites Watch
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137 posts in 2426 days

04-25-2013 04:04 AM

Topic tags/keywords: lathe motor turning

So i’m kinda new to the old wood turning thing. i’ve had an old montgomery ward lathe kicking around forever. found a motor for it last summer, 1/3 horse, 1725 RPm. This matches the spec of what originally came with the lathe. Today I was working on my lathe bench and was doing a mock-up to confirm it was going to work as planned. Motor ran cool with nothing attached, and then with the belt on the empty lathe. But once I put a piece of wood in, that sucker got too hot to touch within about a minute of turning time. A bit of smell too, but no smoke. Motor is old, probably from the 40’s or 50’s, pics to follow shortly. It says ball bearings on the sides where the arbors are bushed, and I don’t see anywhere to oil it.
Are they supposed to get that hot? It does spin freely with no load, and when you plug it in, it just hums for a bit, and then usually needs a spin to get going.

33 replies so far

View murch's profile


1380 posts in 2798 days

#1 posted 04-25-2013 07:37 AM

Mine is a 1/2 hp. It only gets hot enough that you’re glad to put your hands on it on a frosty morning.

Seriously though, electrics is not my area but if a motor is too hot to touch in such a short space of time it’s
probably on it’s last legs.
Hard to know with something that old though. Maybe it’s just loosening itself out and will be fine after some
cleaning and maintenance .

-- A family man has photos in his wallet where his money used to be.

View rustfever's profile


759 posts in 3484 days

#2 posted 04-25-2013 09:46 AM

I have heard somewhere that an electric motor should run at a temperature of not over 40F above ambient temp

-- Rustfever, Central California

View EEngineer's profile


1115 posts in 3787 days

#3 posted 04-25-2013 10:09 AM

when you plug it in, it just hums for a bit, and then usually needs a spin to get going.

This is an indication there is something wrong! If it is capacitor start, check the cap and the centrifugal switch to make sure they are operating. If it has a separate start winding, again, check the centrifugal switch. Are you sure that the motor is ever getting up to full running speed?

Motors are very rugged beasts. You probably have not destroyed it yet running it like this but it will die eventually unless you address the starting issue.

-- "Find out what you cannot do and then go do it!"

View Shawn Masterson's profile

Shawn Masterson

1325 posts in 2122 days

#4 posted 04-25-2013 11:13 AM

Put a meter on it and check the amp draw

View alph's profile


11 posts in 2037 days

#5 posted 04-25-2013 11:54 AM

get a new one, they’re only $50 at harbor frieght. if you have to “spin” it to get it going, it sounds like the bearings are all gummed up, if it’s 50years old, you got your monies worth out of it.

-- alberto angelo

View fumehappy's profile


137 posts in 2426 days

#6 posted 04-25-2013 01:12 PM

EEngineer, what would be the best way to do that? I have a multimeter available to me to check the amperage. I”ve never worked on a motor before, but now is a good a time as any to start…


View fumehappy's profile


137 posts in 2426 days

#7 posted 04-25-2013 01:12 PM

To clarify, there is a cover on the bearings, I just took it off to inspect them.

View dhazelton's profile


2789 posts in 2470 days

#8 posted 04-25-2013 01:58 PM

”...if it’s 50years old, you got your monies worth out of it.” Never. I’d rather spend $50 to refurbish a 50 year old American motor and understand how it works than buy a new Chinese one that will probably burn out in five. These motors are simple to disassemble. Basically once you take those four square nuts off the whole affair just pulls apart. If the bearings are in good shape and don’t feel notchy when you turn the inner race I would just clean and repack. There’s a motor shop near you somewhere, just have to look in the phone book. You can take the capacitor to them to check (the cardboard covered doodad in the base) and they can sell you a new one. The wiring in the base is just wire nutted together I believe so it’s easy to disassemble. Only thing to do with the windings is blow all the dust out or use some CRC electrical cleaner. I would wire in a new 20 amp switch and grounded cord on the front of the lathe stand so you don’t have to use the toggle on the motor base. Make sure you mark the top of the end housing as I think they only go together one way. If it’s running hot you may have the belt too tight which stresses and overheats the bearings. Just pull it apart and clean and repack everything and check the wiring and test it – you have nothing to lose.

View fumehappy's profile


137 posts in 2426 days

#9 posted 04-25-2013 02:05 PM

Yeah, i’ve been doing some research since I posted the pics a little while ago. I want to try the rebuild for that reason, and to learn something for myself. Found this thread on a different site, and I’m going to work off that as a template.

Motor Rebuild

View dhazelton's profile


2789 posts in 2470 days

#10 posted 04-25-2013 02:15 PM

Your motor is significantly easier than that one – I don’t think it has that centrifugal switch assembly for one, and the capacitor is in the base with the rest of the wiring. I redid the exact same motor a couple of years ago, but it ran fine to begin with. It was just packed with sawdust and I replaced the bearings because mine were replacement sealed bearings that felt dry (that’s why I like the original type like you have). You really only need to take off the end where your pulley is, pull out the inner armature and shaft and leave the outer windings alone in the housing. You may find nothing wrong with your capacitor but it may be a loose connection in the base. Have fun.

View REO's profile


929 posts in 2248 days

#11 posted 04-25-2013 02:37 PM

check your pulley diameters, and rpms. you may be high on the spindle rpm and that would make it work harder. Split phase motors have no capacitor or start winding switch the start winding and main windings stay on all the time these motors are for low torque applications. kind of self regulating loads like fans and grinders. you could use it but you would have to limit yourself to extremely light cuts.

View 8iowa's profile


1586 posts in 3935 days

#12 posted 04-25-2013 02:47 PM

dhazelton is spot on. Take it to a motor shop for a little TLC. This motor is worth the expense. I would probably invest in a new set of bearings while it’s at the shop.

I suspect that it is rated 55 degree C temperature rise over a 40 degree C ambient. A 40 degree C ambient translates to a maximum “room” temperature of 104 degrees F. Add the full load temperature rise of the motor (55 degrees C) and you get a maximum temperature inside the motor of 203 degrees F. The outside temperature of the motor won’t be that hot, but since the human limit is around 125 to 150 degrees the motor will be too hot to keep your hands on it. However, the motor is still just fine.

-- "Heaven is North of the Bridge"

View dhazelton's profile


2789 posts in 2470 days

#13 posted 04-25-2013 03:36 PM

@Reo, there is still a little cardboard covered capacitor in the bases of these. If not a start capacitor what is it? I agree with the point that lathe work is hard on a motor and 1/3 HP is not much. Mine powers an old Sears 6×48 belt sander with disc though and it’s fine for that.

View TheDane's profile


5534 posts in 3837 days

#14 posted 04-25-2013 03:40 PM

+1 for taking it to a motor shop. They can either rebuild your motor or make you a good deal on a rebuilt motor they may have sitting on the shelf. The shop I used to deal with (in La Crosse, WI) put a decent warranty on their work.

-- Gerry -- "I don't plan to ever really grow up ... I'm just going to learn how to act in public!"

View fumehappy's profile


137 posts in 2426 days

#15 posted 04-25-2013 03:58 PM

Checking google image search for similiar lathes, the motor pulley does appear significantly smaller. This is just one I picked up at a flea market, so I know it’s not original. I have a smaller step pulley I can try and put on there when I do the cleanout.

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