Is My Lathe Motor Running Too Hot?

[phrog]

I recently bought the Nova Precision Midi Chuck for my HF 34706 lathe which was a Christmas present a few months ago. I've only had a chance to start using the lathe recently. While fiddling with the new chuck, I noticed the motor seemed awfully hot. So I did some experimenting.

Without the chuck on the lathe the motor (ambient temp of 79 degrees) the temperature reached 101 degrees after 5 minutes of no load. After 10 minutes the temperature was 110 degrees. And after 15 minutes, it had reached 123 degrees. With the chuck installed the temps were about the same.

Since there was no wood and no load, it seemed to me this might be a little hot.
What do you think? Is there something wrong or is this about right? Should I limit my turning to a certain number of minutes based on motor temp? What do you guys do? Thanks for any comments or advice.

[woodturner]

Without the chuck on the lathe the motor (ambient temp of 79 degrees) the temperature reached 101 degrees after 5 minutes of no load. After 10 minutes the temperature was 110 degrees. And after 15 minutes, it had reached 123 degrees.

What size and type of motor? Where are you measuring the temperature? What is the total run time on the motor? Does it get any hotter if you run it longer?

Those temperatures seem reasonable for a TEFC motor that hasn't yet broken in, but if it gets hotter than 125 F, something is probably wrong.

Is it drawing excessive current?

[phrog]

What size and type of motor? Where are you measuring the temperature? What is the total run time on the motor? Does it get any hotter if you run it longer?

Those temperatures seem reasonable for a TEFC motor that hasn't yet broken in, but if it gets hotter than 125 F, something is probably wrong.

Is it drawing excessive current?

Thanks for answering Woodturner.

What size and type motor? The motor is a 3/4 HP, 120V, 60 Hz that hangs off the headstock (not enclosed).

Where are you measuring the temperature? In the garage. Just kidding. I measured it about 1/2 inch above the steel casing and about an inch behind the start capacitor. (Little if any air movement there)

What is the total run-time on the motor? Guessing about 8-10 hours.

Does it get any hotter if you run it longer? I haven't tried running it longer because I wondered if 123 degrees was getting hot enough to ruin it.

Is it drawing excessive current? I have no idea how to measure current draw but can tell you that it hasn't tripped a circuit breaker yet.

Again, thanks.

[Tom Slick]

Unless it gets so hot you can't touch it then don't worry. 123* is not harmful for an electric motor.

[Daryl]

If you are running it off an undersized extension cord there likely would be some over heating.
You need a clamp on ammeter to measure the current draw.

[woodturner]

Thanks for answering Woodturner.

What size and type motor? The motor is a 3/4 HP, 120V, 60 Hz that hangs off the headstock (not enclosed).

I'm assuming it has a fan? What is the rated Full Load Amperage (FLA) - it should be on the nameplate on the motor.

Where are you measuring the temperature? In the garage.

Everybody is a comedian

Does it get any hotter if you run it longer? I haven't tried running it longer because I wondered if 123 degrees was getting hot enough to ruin it.

The first sign of a motor getting too hot is often an "insulation" smell. If you notice a difference, acrid smell, I would turn it off.

I would suggest a couple of things:

1. Make sure the pulleys are aligned - pulleys that are not quite aligned can push the motor shaft against the bearings and cause it to run hotter than normal.

2. Are the bearing sleeve type bearings? If so, do they have oil caps or need lubrication? If so, make sure they are lubricated.

3. Another poster mentioned extension cords. Is the FLA of the motor within the capacity of the branch circuit? If you are using an extension cord, make sure the wire is large enough (at least 12 guage, preferably 10 guage, assuming your motor is 15A FLA).

4. Check the voltage at the receptacle, ideally with the motor running. It's possible there is a wiring issue or other cause of low voltage, which can cause motors to run hot.

Hope this helps.

wt


Is it drawing excessive current? I have no idea how to measure current draw but can tell you that it hasn't tripped a circuit breaker yet.

Again, thanks.[/QUOTE]

[eezlock]

motor running too hot?

I don't think that is excessive for that motor by what you have said...but I would keep an eye on it all the same.If it were to get so hot that it would be unsafe to touch the outside case of the motor.....then I would begin to have concern. When you install the chuck and a piece of rough wood to start turning
that adds extra weight, mass, volume to the motor...all those factors can and will cause some extra heat to build up in the motor for a while. After a few minutes of turning.....let the lathe spin free to help disapate the heat...won't hurt anything, but will aid in cooling the motor.

[phrog]

Firstly, let me thank everyone who has replied to this post.

Secondly, I've tried letting the lathe run longer with the following results:
77* Ambient
92* After 5 Minutes
114* After 10 Minutes
126 * After 15 Minutes
138* After 20 Minutes
144 * After 25 Minutes
149* After 30 Minutes
152* After 35 Minutes
158* After 40 Minutes
164* After 45 Minutes
I stopped the experiment here due to fear of a melt-down.

In response to previous questions and comments let me state the following:
The pulleys appear to be aligned okay to me. I see no wobble. I don't know what sleeve-type bearings are but my instruction manual does not mention anything about lubricating bearings; so I assume that is not the problem. I'm not using an extension cord. Tool is plugged directly to an outlet which is about 10 feet from the supply box with a 12g line. The circuit breaker is a 20amp. The voltage at the receptacle is measuring 120 with the tool running. There is no amperage statement on the motor or machine anywhere that I can find. The electric cord is not the least hot; only the motor casing.
I do not smell anything unusual but I've been told that I don't smell good.

My question is: Do you ever run a lathe this long (or longer)? Should I be concerned?

Again, thanks to all who have responded.

[Tom Slick]

I don't have a specific answer if you actually have a problem but if it makes you feel any the lowest max temp. rating for electric motor windings is about 220*f some are rated as high as 350*f. The lowest rated motor allows a 140*f temp. rise over ambient. You are not anywhere near a meltdown.

Does the motor seem to have power when under load?

[woodturner]

164* After 45 Minutes

My question is: Do you ever run a lathe this long (or longer)? Should I be concerned?

164F is abnormally hot, even though technically within spec as Tom noted. I regularly run my lathe for more than an hour at a time, and the motor never gets too hot to touch, even with a large blank or chuck.

I looked on the HF site and your lathe has a 1 year defect warranty. It appears it is within the 1 year, so I would take it back. I'd probably talk to the store first before I drug it down there - maybe they can give you another motor or something like that, or maybe there is a known issue that they will know about. You could also try the customer service phone number.

There is no amperage statement on the motor or machine anywhere that I can find.

6 A according to the HF product page. Seems low for a 3/4 HP motor.

[LCHIEN]

...



6 A according to the HF product page. Seems low for a 3/4 HP motor.

6A is about right... that's 720 watts. 720 watts = .96 HP if the motor is 100% efficient. If the motor is about 75% efficient (probably a reasonable number) the numbers are right.

Looks like that lathe has a variable diameter pulley system to change speeds, I would guess it might have some friction load. Still its a wild guess but just spinning you might be drawing 2-3 amps. If it's 75% efficient then the motor itself would be dissipating around 75 watts. THink of a 75W light bulb in a metal box of that size -

Offhand the temps sound high. you need ammeter to check (like a kill-a-watt meter, they're cheap and very easy to use,) Also I don't see how you can measure the temperature a 1/2 inch away in free air very consistently. The case temperature would be a much better indicator and probably hotter.

[phrog]

I don't have a specific answer if you actually have a problem but if it makes you feel any the lowest max temp. rating for electric motor windings is about 220*f some are rated as high as 350*f. The lowest rated motor allows a 140*f temp. rise over ambient. You are not anywhere near a meltdown.

Does the motor seem to have power when under load?

Yes, Tom, the motor does have power under load. Thanks for the info - it makes me feel better to know that I'm probably not headed for an immediate meltdown. (or a splash of molten copper while turning)

[phrog]

164F is abnormally hot, even though technically within spec as Tom noted. I regularly run my lathe for more than an hour at a time, and the motor never gets too hot to touch, even with a large blank or chuck.

I looked on the HF site and your lathe has a 1 year defect warranty. It appears it is within the 1 year, so I would take it back. I'd probably talk to the store first before I drug it down there - maybe they can give you another motor or something like that, or maybe there is a known issue that they will know about. You could also try the customer service phone number.



6 A according to the HF product page. Seems low for a 3/4 HP motor.

Thanks WT for the practical info. Just getting started in turning, I really didn't know how long a practical session would last. I thought about the warranty when I realized my motor was pretty hot. I looked and I'm covered through Feb of next year. I think I may talk to the HF manager about it and get his opinion. Again, thanks for your continued input.

[phrog]

6A is about right... that's 720 watts. 720 watts = .96 HP if the motor is 100% efficient. If the motor is about 75% efficient (probably a reasonable number) the numbers are right.

Looks like that lathe has a variable diameter pulley system to change speeds, I would guess it might have some friction load. Still its a wild guess but just spinning you might be drawing 2-3 amps. If it's 75% efficient then the motor itself would be dissipating around 75 watts. THink of a 75W light bulb in a metal box of that size -

Offhand the temps sound high. you need ammeter to check (like a kill-a-watt meter, they're cheap and very easy to use,) Also I don't see how you can measure the temperature a 1/2 inch away in free air very consistently. The case temperature would be a much better indicator and probably hotter.

Wow, Loring, where do you get all those numbers? (You must be an EE.) I took three years of college physics (long, long ago) but remember very little about electricity.

The temps were measured with a non-contact thermometer about a 1/2 inch from the motor housing. I realized this was not too scientific but would give a reasonable relative estimate. I'll look into an ammeter. Until now, I've never needed one. Thanks much for your comments and advice.