Soft Start for Lathe?

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BadDog
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Re: Soft Start for Lathe?

Post by BadDog » Fri Apr 26, 2019 4:43 pm

Not sure how it would really be directly relevant as long as you are trying to spin it in "neutral" (between H/L or Back/Direct), but are you certain it is a "gear head"? Do you have multiple levers that you throw to get specific gears to control rpm? Or does it have a variable speed, typically based on a Reeves type belt drive?

I looked for some old Jet lathes sized and dated as you describe, and they all appear to be direct drives. If it's not a gear head, then some of the specifics on how to proceed and what to check will change. Gear heads are oil bath, either slung or pressure feed that require very infrequent service. Direct drives typically have an open head casting that requires periodic service, specifically to access and lubricate the back gear and dog clutch mechanism.
Russ
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BadDog
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Re: Soft Start for Lathe?

Post by BadDog » Fri Apr 26, 2019 4:49 pm

This is an example of an old Jet 10x24. It's unusual in that it has small oil reservoirs and sight glasses for the main and support bearings, but is a direct drive with back-gear, not a gear head. Another tell-tale is the drive-side banjo tumbler, where gearheads (that I know of) use an internal reversing gear with shift fork.
Image


This appears to be a nice reference site. I can't link pictures because of the size restraints.
Jet 10x24
Russ
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RMinMN
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Re: Soft Start for Lathe?

Post by RMinMN » Sat Apr 27, 2019 7:20 am

One picture is worth a thousand words and in this case it might be worth more than the thousand words. Open the top of the headstock and take a picture of the inner workings. That would instantly show what kind of lathe you have.

Circuit breakers can come in fast break or slow break. The slow break will allow higher currents for a split second to allow motors to come up to speed. You may need one of these. Even with the slow break one can trip them with multiple starts. My tablesaw will do that occasionally as during each start up current will bring the breaker part way to tripping and with enough starts will trip it.

The motor on your lathe and mine are probably identical, a 1 HP capacitor start motor. There is no soft start to these motors but there shouldn't need to be as the lathe is sufficiently underpowered that the motor will do no damage as it comes up to speed. My chucks screw directly onto the spindle and will not unscrew with starting in reverse if tightened properly because there is insufficient torque in startup to do so. Being a capacitor start induction motor one cannot go from forward to reverse without stopping the lathe as one could with a 3 phase so that won't affect the startup.

David2011
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Re: Soft Start for Lathe?

Post by David2011 » Sat Apr 27, 2019 1:22 pm

Russ,

You made a light come on for me. I never understood exactly what the term 'gear head" meant. I had confused quick change and gear head just because I didn't know the correct terminology. I have only had a little instruction on lathes and mills; mostly self taught. Yes, it is clear now. That is identical to my lathe other than the power switch.

RNinMN, I've been inside the headstock a zillion times lubricating and changing in/out of back gear but I didn't know the difference between direct drive and gear head even though I have used a gear head lathe in the past. I just knew that some required moving a belt and others required moving levers to change speeds. I appreciate the help in getting the terminology right. Like yours, this is a screw on chuck. I've changed chucks many times when I needed a 4 jaw but lately everything has been new projects so the 3 jaw has been all I needed. I haven't had any issues running it in reverse but I haven't needed to use reverse much.

Now that I know the right words, if I ever get another lathe it will most likely be a gear head with a clutch, unless a nice piece of old American iron falls in my lap. Even though they're an old design I like the South Bend 13"-14" lathes. Getting a good one is becoming more difficult.

David2011
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Think I found the problem

Post by David2011 » Sat Apr 27, 2019 1:41 pm

Oops! I typed the previous response earlier today and then failed to submit it.

Some time later, I worked with the lathe going through everything I could think of before pulling the bearing caps. With the tumbler disengaged there was not much noise coming from the lathe. I cleaned and lubed the gear train and took a look at the belts. The spindle belt seemed excessively tight with only about 1/4" of deflection so I took a link out of it and adjusted the tension. The motor belt also seemed too tight so I backed the tensioner until it also had about 1/2" deflection. I ran the lathe on all speeds without tripping a breaker. I haven't made any chips yet but I couldn't start the lathe at any of the high range speeds without tripping the breaker. Now it starts and runs happily at all speeds. I ran it with the tumbler engaged and disengaged at all speeds and without a doubt the whine I described earlier is from the straight cut gears. Time will tell if that was all there was to the problem. I can look back and correlate the changing of the belts with when the popping of the breaker. Both occurred about the time I moved into the current house. My time with the lathe will be limited in the coming weeks as we try to complete a move from New Mexico to the Houston area.

Earlier I said I hope I didn't sound like an idiot. Now I feel like a total idiot overlooking something so simple.

Thank you all for the help and encouragement in finding the source of the problem!

David

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Re: Soft Start for Lathe?

Post by Glenn Brooks » Sat Apr 27, 2019 1:53 pm

Sounds promising. Particularly the bearing caps. That suggests you might have split bearings- solid yellow metal spherical castings, split in half. If so, similar/identical to my 1919 circa Dalton lathe. These are easy to work with. First off, put a dial test indicator on the chuck and insert bar stock in the spindle and pull upwards. Proper tension on the spindle will result in .002” upwards movement. (.002 clearance allows for a film of lubricating oil between spindle and bearing surface.).

More clearance means the bearings are worn and/or loose. Less means the spindle is binding against the overly tightened bearing cap, causing the spindle to not turn and the motor to stall. This could be your problem. Try loosing the bearing cap screws and measuring the spindle play. Then set it properly with shims undermthe bearings and try your motor again. If it trips the breaker, try going to the 30amp breaker.

FWIW,my experience is the bearing caps come looser over time, not tighter. So all of the above might not mean anything...

Still, it’s always good to check spindle play every once in awhile, to assure precision matching if nothing else.

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David2011
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Re: Soft Start for Lathe?

Post by David2011 » Sat Apr 27, 2019 4:59 pm

I'll check the spindle play. The bearings are conventional tapered roller bearings held in place with end caps. No split bearings. I've run the lathe at its highest speed a few more times today and it hasn't tripped the breaker yet so even if the belts were not the entire problem they were certainly a big factor.

Everything I've machined on the lathe for a long time has been at 295 rpm except for threading. I'm looking forward to the improved flexibility.

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SteveHGraham
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Re: Soft Start for Lathe?

Post by SteveHGraham » Sat Apr 27, 2019 5:00 pm

A cap can't dump charge until it stores it.

I build guitar amps that use capacitor pi filters. One of the concerns with high capacitance is sucking a huge amount of current as soon as the amp is turned on.

Electrolytics go bad over time. I don't know if they ever develop momentary internal shorts that would cause breakers to pop, but they do blow up and so on. I didn't know it was possible for an electrolytic to last 41 years.
Every hard-fried egg began life sunny-side up.

David2011
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Re: Soft Start for Lathe?

Post by David2011 » Sat Apr 27, 2019 6:28 pm

Steve,

I know you're right about a cap having to charge up before it can dump but if a motor is being started and stopped repeatedly the cap should still have a charge from the last time the lathe was running. OTOH, maybe at its age it isn't holding a charge for very long. Not gonna stick my tongue to it to test. I know how to test voltage retention with a voltmeter and resistor but it's just too easy to replace it. An American made 400 MFD cap (that's the spec on the motor data plate) is only $11.00. We're in the process of moving to our new house so I'll replace it when I move the lathe.

John Hasler
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Re: Soft Start for Lathe?

Post by John Hasler » Sat Apr 27, 2019 8:14 pm

> I know you're right about a cap having to charge up before it can dump but if a motor is being started and stopped repeatedly the cap should still have a charge from the last time the lathe was running.

When the motor slows down after you shut it off the centrifugal switch closes, discharging the capacitor through the windings. Retained charge would have little effect anyway: there just isn't that much energy there.

David2011
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Re: Soft Start for Lathe?

Post by David2011 » Sat Apr 27, 2019 10:29 pm

Ah, that makes sense. That's different from an air conditioning motor or other capacitor start motors that don't have starter windings. So much I have learned about other similar stuff is different with this motor. I didn't think about the switch discharging the cap. Thanks!

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NP317
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Re: Think I found the problem

Post by NP317 » Sat Apr 27, 2019 10:36 pm

David2011 wrote:
Sat Apr 27, 2019 1:41 pm
[snip]
Earlier I said I hope I didn't sound like an idiot. Now I feel like a total idiot overlooking something so simple.
[snip]

Don't feel bad about not knowing things.
My past learning experiences are like my machine shop's scrap box: Filled with the results of ignorance, followed by "Uh, Duh!"

Fortunately you are smart enough to ask!
Welcome to the learning process.
~RN

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