Jack shaft overheats.

mjhenks

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I rebuilt my LOGAN 400 a few years back. I also built a variable frequency drive and installed that at the same time.

The jack shaft Has new bronze bushings and I made a new SS shaft for it to overhang farther for the larger Baldor 3PH motor.

The jackshaft assy runs smokin hot. It overheats is 5 min at moderate speed. I have oiled it and the belt tension is not high. Not totally sure why right now. Fits on the bushings seem fine and it turns freely until it overheats.

Has anyone ever installed ball bearings in their jackshaft? Looking for a solution or understanding on why.

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First guess is the moment is too large.

The length of unsupported shaft caused much pressure on the bearing and it is possible that the pressure causes the oil to be pushed out of the way like a wiper due to the pressure.

A ball bearing would help but moving motor so pulley is in correct place would be better.

To test loosen tension so it just barely holds and see if it running this way runs any cooler.

Which bushings are getting hot?

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I tried to keep it as short as possible so totally understand your point. Will test with almost not belt tension. Darn 3PH motors are way bigger than original.

Both bushings get hot at about the same rate.


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Agree with above Belt is out too far
If both are getting hot then something is not right.

"New" bushings.

What you mean "new"?

Original replacement parts or Something made or general replacement type thing?

If the bushing is not an oil impregnated type then it needs to retain a film to work.

That means a somewhat critical sizing that depends on the lubricant type.

You could consider honing out a bushing to allow a bit of oil to form a film.

Another trick is to place o - rings on the bare shaft against the bushing to retain the oil a bit.

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New meaning oil lite bearings from McMaster Carr with the right OD but were bored for the ID. Fit i do not recall exactly but was with-in .0005" if the shaft OD. I have oiled the bearings anyways to see if that would help. The bearing visually takes the oil in from the top original oil holes and the oil can be seen exiting the bearing after a while.

I am going to do some testing to confirm it is just the shaft overhang and will report back. If it is that then i will be in a pickle on how to fix it and retain the lever arm to switch pulley's in the head stock.
 
I would agree with tq60 that the shaft needs to be supported closer to the motor. I would also bet the rpm is too high for the bronze bearings. I have a similar setup on an old Seneca Falls machine with a 1750 rpm motor and an almost 12 to1 reduction between the motor and the jackshaft. In this case the maximum spindle speed is about 650 rpm. There has never been a problem with the jackshaft bushings overheating.

I also have a Sheldon machine that uses a jack shaft setup. This setup uses pillow block ball bearings. Also there's very little distance between the driven pulley and the bearing. I can run the spindle speed on this machine up to 2,200 rpm without problems.

Sheldon Jackshaft assembly.

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Seneca Falls jackshaft assembly.

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Can you turn the motor around and move the pulley next to the bearing, may have to make traveling motor mount
Motor should be reversible. Didn’t see any oil cups or on bearing bosses may be a good idea to add a couple .
Just a thought
 
The other thing I just noticed is your motor and jack shaft pulley ratios.
On small Logans the shaft pulley is LARGER than the motor pulley. It looks to me as though the shaft is
turning much to fast and you're compensating with the VFD.


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Here's the pulley setup on a Model 200.


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Here's a pic of a Model 400 I just found online:

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You know the saying speed kills. Also I know they say you don't need to but did you drill a hole thru the bushing so oil gets to the shaft? I agree your pulley system is over speeding the lathe itself. It's old not a 2,000 rpm machine. Just guessing if your motor is 1750 your pushing the Jack over 2,750 to 3,500 rpms. Melting the bushing quickly
 
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