Soft Start for Lathe?

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David2011
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Soft Start for Lathe?

Post by David2011 » Wed Apr 24, 2019 6:16 pm

For years I've lurked on this forum soaking up lots of good info. Now I have a question. My lathe is a 1978 Taiwanese Jet 10x24 that I like very much. It's a real lathe weighing in at about 600 pounds with the 3 jaw chuck and as capable as my skills. It came from a friend that was no longer able to use it. He got it and a Taiwanese copy of a Bridgeport mill in around 1982 and I bought them from him 11-12 years ago, none of which has much to do with the question.

The lathe tends to pop a 20A circuit breaker infrequently at its lowest speed and much more frequently on higher speeds. The motor is a 110V 1 HP model. I had the bearings in the motor replaced a few years ago but later realized it was probably the startup disengage that I was hearing as it spooled down. The motor repairman tested the current draw on his bench and said it was normal for the power of the motor.

In my mind it is clearly popping the circuit breaker due to the mass that the motor is trying to accelerate. There is no option to start the motor and then engage the gear train. The options as I see them are to run 10 GA wire and install a 30A breaker or to install a soft start device.

Has anyone used a soft start device to remedy this problem? Any recommendations on one option or the other? The existing wire is 12/2 and runs about 30 feet from the breaker box.

John Hasler
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Re: Soft Start for Lathe?

Post by John Hasler » Wed Apr 24, 2019 7:35 pm

You can go to a 30A breaker without replacing the 12/2 as long as the lathe is the only thing on the circuit. Branch circuit rules don't apply here.

pete
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Re: Soft Start for Lathe?

Post by pete » Wed Apr 24, 2019 7:38 pm

If it were me I'd first start by removing the drive belts and spin everything over by hand to make 100% certain there's nothing mechanical causing enough drag to sometimes kick the circuit breaker out. Mis-adjusted bearings, dry bushings, old congealed oil etc. Your not using grease anywhere in there by mistake are you? Circuit breakers can also get old and a bit weaker so that might? be part of the problem. At the low speed belt position there should be ample motor torque available to never trip a 20 amp breaker even with a heavy chuck and work piece. Somethings certainly not correct and I'm suspecting you've got a higher than normal mechanical drag somewhere between the motor, spindle and the carriage when power feed is being used. My using the wrong oil thinking I knew better than the factory recommendations cost me a $800 lathe motor one time just because the oil dried out, got sticky and caused enough drag to burn out the motor. I'd like to think I'm now a bit older, possibly a bit smarter and today I don't second guess the lube recommendations for anything.

Glenn Brooks
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Re: Soft Start for Lathe?

Post by Glenn Brooks » Wed Apr 24, 2019 9:07 pm

Iam with Pete on this. Sounds like something is dragging on the motor or drive chain to pop the circuit breaker. An excessive drag would cause the motor to work harder and maybe temporarily exceed your load rating. -Or some other load comes on line in that circuit, a shop heater maybe,(?) and adds enuf load to exceed the 20 amp rating.

Out of curiosity, what is the amperage rating stamped on the motor plate? If it’s high, like 13- 15 amps then yes you might be seeing an occasional peak amperage draw over 20. Particularly if you are stalling the motor with a heavy, overly fast or deep cut, But, seems unlikely.

Also, I assume you do not have a VFD in line in this circuit? Some VFD’s trip GFCI equipped circuits, as the low voltage control circuit in the VFD makes the GFCI think it’s in a short condition (when it is not).

Glenn
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David2011
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Re: Soft Start for Lathe?

Post by David2011 » Thu Apr 25, 2019 3:40 am

Pete, Glenn,

Thank you for excellent responses. They've gotten me thinking.

Just came in from the patio binge watching a TV series. I'm currently in SE New Mexico and it's just getting warm enough to sit on the patio in the evenings if the wind is light. Retired so time of day is less important. The breaker was replaced and it didn't make any difference. I'll remove the drag from the motor and see what happens but based on past tests I don't expect it to pop a breaker unloaded. I always start it with the bit off of the workpiece and power feeds disengaged. It has popped the breaker while making a cut a couple of times but that's rare. I seldom make heavy cuts and rarely work on anything over 2" OD. Now that I think about it I don't believe it ever popped a breaker at my last house. I've been in the current house and shop about 8 years. I built out the insides of a metal building that was on the property when I bought it. There's a 200 amp feed from the house to the shop. I ran lots of new wiring to accommodate the machinery room and two other rooms that are all insulated, air conditioned, good lighting and so on. All wiring was done to code and I made it a point to isolate the machinery from lighting and other draws. There is nothing on the lathe circuit other than the lathe and a single light on the lathe. Every air conditioner is on a different circuit. Lighting is on separate circuits from the wall outlets. I'll look tomorrow and see what the data plate on the motor says is a nominal draw. When it was tested at the motor shop the draw was between 9-10 amps. The motor guy said that was normal; that 110VAC motors generally consumed as much electricity idling as under a normal load but that is different from the startup load.

In its normal configuration turning the chuck manually turns the motor. Last night I released the pressure on the V-belt and turned the chuck. It does not turn easily like I see even much larger lathes turn in how-to videos. I taught gunsmithing at a community college and had an opportunity to use both ancient but lovable 14-1/2" South Bends and a brand new 14x40 (Enco if I remember correctly) that had a freewheeling by comparison spindle. It's been a few years but it seems like even the South Bends turned more easily than this Jet with the belt released.

There's no VFD in the circuit and no GCFI..

The only place that's greased is the gears. The recommended lubricant is chain lube. All other lube points call for SAE 30 WT motor oil. I think there's a good chance that the spindle bearings should be pulled, cleaned and lubed; replaced if necessary. The precision is still good but it whines at high speeds.

So far this does sound like a problem with old lubrication, doesn't it? I have a couple of gallons of kerosene on hand and will clean up the headstock's moving parts.

John Hasler
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Re: Soft Start for Lathe?

Post by John Hasler » Thu Apr 25, 2019 9:53 am

> Now that I think about it I don't believe it ever popped a breaker at my last house.

You may have had slightly higher line voltage there. That plus the voltage drop in that 30' run may have pushed the starting time * current product up just enough.

> Last night I released the pressure on the V-belt and turned the chuck.
> It does not turn easily like I see even much larger lathes turn in how-to videos.

Not good. Do the bearings get hot?

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ALCOSTEAM
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Re: Soft Start for Lathe?

Post by ALCOSTEAM » Thu Apr 25, 2019 10:49 am

If its a single phase motor you could be having the start switch sticking once in a while. The start windings draw a good bit of amperage that is NOT included in your motor nameplate ratings. It could also be a start winding beginning to fail. The high inrush and large magnetic fields can jiggle and loosen windings to where they rub and begin to short out or break and make an open winding.
Do you have an amp meter? Knowing what is really going on can make a big difference in diagnosing a problem. Also its not uncommon to oversize your overcurrent protection on a motor, and sometimes it can be several times the value of your motor nameplate ratings.

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SteveHGraham
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Re: Soft Start for Lathe?

Post by SteveHGraham » Thu Apr 25, 2019 11:13 am

I wonder if your breaker is going bad. My understanding is that breakers will generally let you get away with a very brief surge, which is probably why power surges fry electronics.

You can get a breaker which is designed to have a little more give without going up in amperage.

A new breaker would be cheap, and you could replace it in 10 minutes.
Every hard-fried egg began life sunny-side up.

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BadDog
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Re: Soft Start for Lathe?

Post by BadDog » Thu Apr 25, 2019 11:44 am

I think he said he just replaced the breaker with no improvement. And I think the slow breakers like used for big transformer welders are what you are talking about.

But I think you already found your problem. I've got a big 17" lathe, and with the drive disconnected, the spindle rolls relatively freely.

Assuming it's a gear head, the high rpm whine could be just the straight cut gears, not bearings.
Russ
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whateg0
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Re: Soft Start for Lathe?

Post by whateg0 » Thu Apr 25, 2019 12:45 pm

Is a GFCI breaker? I have a buddy who has GFCI on one wall and he can't start his mill without it tripping.

Dave

David2011
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Re: Soft Start for Lathe?

Post by David2011 » Thu Apr 25, 2019 4:35 pm

ALCOSTEAM wrote:
Thu Apr 25, 2019 10:49 am
If its a single phase motor you could be having the start switch sticking once in a while. The start windings draw a good bit of amperage that is NOT included in your motor nameplate ratings. It could also be a start winding beginning to fail. The high inrush and large magnetic fields can jiggle and loosen windings to where they rub and begin to short out or break and make an open winding.
Do you have an amp meter? Knowing what is really going on can make a big difference in diagnosing a problem. Also its not uncommon to oversize your overcurrent protection on a motor, and sometimes it can be several times the value of your motor nameplate ratings.
When the breaker pops it happens virtually instantly, well before the motor has time to spin up. It might make ¼ turn at the chuck. I don’t have an inductive amp meter.
John Hasler wrote:
Thu Apr 25, 2019 9:53 am
> Last night I released the pressure on the V-belt and turned the chuck.
> It does not turn easily like I see even much larger lathes turn in how-to videos.

Not good. Do the bearings get hot?
Never noticed them being anything more than warm. When I “spin” the chuck it only coasts for about a half turn. There’s no roughness but I would think that much weight/inertia would be good for a full turn or more. Am I overly optimistic there? I took the belt off of the pulley to check. If I spin it by hand one way and then the other I hear a tick from the bearing(s) when I reverse the direction. Is that tick cause for concern?
Hope I’m not coming across like an idiot. I know a lot about a lot of things but have never done any troublehooting on a lathe. I’ve built accurate rifles, 2 street rods, restored some fabric covered airplanes and refit a 28’ sailboat from the top of the mast to the bottom of the keel touching literally everything on the boat. This is on a very different level than all of that other stuff.
Glenn Brooks wrote:
Wed Apr 24, 2019 9:07 pm
Out of curiosity, what is the amperage rating stamped on the motor plate? If it’s high, like 13- 15 amps then yes you might be seeing an occasional peak amperage draw over 20. Particularly if you are stalling the motor with a heavy, overly fast or deep cut, But, seems unlikely.
Glenn
Checked the motor plate. It says 13 amps. It’s a reversible capacitor start induction motor. After a little Internet searching I found a formula for calculating the startup draw based on motor class. The plate says it’s a class H motor so at 1 HP the startup current can be from 31.7 to 37.2 amps at 110VAC and a little less at 120VAC. Maybe the breakers at this house are faster acting than those at the last house. They’re not the same brand as those at the last house.

There’s as much mass in the gear train of this lathe as I’ve seen in some 14” lathes.

David2011
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Re: Soft Start for Lathe?

Post by David2011 » Thu Apr 25, 2019 4:38 pm

To clarify on the friction of the spindle, when I see the clutched medium lathes turned by hand they look to be nearly friction free. Mine has some drag.

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