smoke coming out of 9729 lathe motor connector box

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John R
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Location: Sour Lake, Texas

smoke coming out of 9729 lathe motor connector box

Post by John R » Fri Jul 31, 2020 3:44 pm

I've done quite a bit of lathe work the last week and just now I noticed smoke coming out of the connector box on the lathe motor. I took the cover off of the box and could see no evidence of fire or blackened wires or anything like that, so put the box back on the tried the motor again. Same thing; smoke coming out of the box - actually out of the black grommet and screw in cap where the power cord enters. The motor didn't stop and the lathe turns but obviously I don't want to use it like this. I did a search on this on here and nothing came up. The lathe switch works fine it turns the motor off/on both forward and reverse.

This 9729 is ?? 12-18 years old and I've used extensively during that time.

Does anyone have any ideas here?

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NP317
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Re: smoke coming out of 9729 lathe motor connector box

Post by NP317 » Fri Jul 31, 2020 3:58 pm

I would first check for loose screw connections on the wires in the box.
If you have a hand held temperature gauge that can help you find a heat source without sacrificing finger skin.

With use and current cycling it is not unusual for screws to work loose, increasing resistance in the connection, leading to heat buildup.
If you find loose screws, remove them to fully inspect the wire connections and clean them as needed.

For future security you can add some conductive joint compound to the connections before putting them back together.
I found a tube of that goop at my local hardware store, which I used when assembling 220V ac wiring for our kitchen stove I replaced.
That was to meet electrical code requirements.
No smoke or flames yet...
RussN

John R
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Location: Sour Lake, Texas

Re: smoke coming out of 9729 lathe motor connector box

Post by John R » Sat Aug 01, 2020 1:46 pm

I looked again just now and the smoke is coming out of the electric motor case where the wires pass through into the connector box. I'm going to order a new motor from grizzly.

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liveaboard
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Re: smoke coming out of 9729 lathe motor connector box

Post by liveaboard » Sun Aug 02, 2020 4:12 am

I'm not familiar with that machine, but generally speaking electric motors are standard items and you can order a motor with the same power, rpm, and frame from any electrical supply for far less than a spare part from the lathe manufacturer.

I would advise a 3-phase motor and matching VFD.
I added a VFD to my ancient Czech lathe and it's a huge improvement, very worthwhile.

John Hasler
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Re: smoke coming out of 9729 lathe motor connector box

Post by John Hasler » Sun Aug 02, 2020 7:44 am

liveaboard wrote:
Sun Aug 02, 2020 4:12 am
I'm not familiar with that machine, but generally speaking electric motors are standard items and you can order a motor with the same power, rpm, and frame from any electrical supply for far less than a spare part from the lathe manufacturer.

I would advise a 3-phase motor and matching VFD.
I added a VFD to my ancient Czech lathe and it's a huge improvement, very worthwhile.
What he said. You can almost certainly get a better motor than what Grizzly would sell you for less money.

It might also be possible to get that motor rebuilt, though that might not be cost-effective. If it were mine I'd tear it down and see if I could fix it: motors are really simple.

Torch
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Re: smoke coming out of 9729 lathe motor connector box

Post by Torch » Mon Aug 03, 2020 6:11 am

Those motors are 3/4 hp AC induction TEFC motors, correct? Probably the thin varnish insulating the windings has deteriorated from heat over time and now one or more windings are shorting. The motor will not last much longer. You could get it rewound if there is a motor or armature repair shop in your area, but it might be more economical to replace.

And if you are going to replace it, this is an opportunity to upgrade it. I would not go bigger than about 1-1/2 hp, just because the machine and it's associated switches and wiring are not heavy enough for a bigger jump. Variable Frequency Drive is one option. Another is DC. One popular upgrade on these machines is to source a DC treadmill motor. You may be able to get a controller from the same scrap treadmill or you can buy a Pulse Width Modulated controller separately.

The advantage of VFD or PWM is variable speed with good low-speed torque. Add a tachometer to display the spindle speed and you can dial in the exact RPM you want on the fly.

The disadvantage is greater cost and the complexity of wiring it in.

John R
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Re: smoke coming out of 9729 lathe motor connector box

Post by John R » Mon Aug 03, 2020 6:34 pm

20190420_160424.jpg
Guys I've already ordered and paid for the Grizzly replacement. It's on back order and according to Grizzly the next batch will arrive on 8/25. This thing (the 3 in 1) is a tool to me and not a hobby in itself. Thus I'm into the most simple/easiest fix and not some exotic do over even it would be better/stronger after I've done it. I'm no electronics expert so would really have to study up to do the things you are suggesting and am just not into it. Oh I could do it I think but I just have no interest in doing so. I'm 75 years old, bought this thing well used 12-18 years ago, and if the replacement motor I'm buying lasts as long and this original motor that is probably well longer than I will last. I appreciate the input though.

The main thing I do with this machine is replicate oem carburetor linkage from mid-50s to mid-60s muscle cars. Not heavy duty work but one needs a lathe and mill to make it look right.
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