Need "Rule of Thumb" advice for Oilite bushings.

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Electrojim
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Need "Rule of Thumb" advice for Oilite bushings.

Post by Electrojim » Tue Jan 18, 2022 5:10 pm

Need a bit of guidance here.

I've got a turntable, part of an old piece of sound recording equipment that I'm restoring. The turntable has a dead-nuts-on 0.750" steel shaft that drops into a cast aluminum well and sits on a nylon ball at the bottom. Problem is that the well ID is too sloppy and there's noticeable play when you rock the turntable from opposite edges. I have the feeling that steel on aluminum might not make the best bearing anyway; other turntables from this era (1950s) had bronze sleeve bushings pressed into the well.

What I'd like to do (or have done, actually, as I don't have the proper equipment and even less skill) is bore-out the well to 7/8" and press-in a couple of 1-inch-long thinwall Oilite bushings: one down to the bottom of the well, the other flush with the top. This would leave an inch or so in the center that could form an oil reservoir. Question is, for a shaft that's exactly 3/4", would I use .751" or .752" ID bushings, and what size bore-out would I specify for the hole? I don't have a feel for how much such a bushing might shrink as it's pressed-in. In operation there would be very little side load on the bushing.

All ideas welcome; thanks for the help.

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Bill Shields
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Re: Need "Rule of Thumb" advice for Oilite bushings.

Post by Bill Shields » Tue Jan 18, 2022 10:40 pm

Were it me I would get the size to size ID bushings you need...have someone bore the frame out slightly oversize and loctite the bushings in place

This way you to not need to worry about ID size after pressing into place.
Too many things going on to bother listing them.

Electrojim
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Re: Need "Rule of Thumb" advice for Oilite bushings.

Post by Electrojim » Wed Jan 19, 2022 12:06 am

That sounds like a safe bet. I was afraid that after squeezing the bushings they might have to be reamed, which I don't think Oilite likes much. Thanks.

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Bill Shields
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Re: Need "Rule of Thumb" advice for Oilite bushings.

Post by Bill Shields » Wed Jan 19, 2022 10:42 am

You are correct...but it can be done.

A modern alternative could be a synthetic bearing held in place with loctite.

Concern would be that if the bearing wall is too thin....the loctite can actually cause the bearing to compress va bit thereby effectively reducing the ID
Too many things going on to bother listing them.

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Rich_Carlstedt
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Re: Need "Rule of Thumb" advice for Oilite bushings.

Post by Rich_Carlstedt » Wed Jan 19, 2022 5:20 pm

Rule of thumb is to know what the ID and OD of what the oillite bushing has
The OD's are larger than standard size and so is the ID.
That is so that the "Bore" of the housing determines finish ID bore size
Hypothetical numbers here as it has been a few years since I did this at work
.. And remember that Oillite bearings are somewhat elastic , being made from powdered metal
So take a 3/4 " OD bushing with a 1/2 " bore ( ie !)
The bushing will have a .753 OD and a .502 bore.
So if you want a .500 bore , you need a .002" compression , and that means the housing should have a .751 bore
Manufacturers make the bores , so subsequent replacements are on size.

It also helps that when inserted , that the tool match (!) the desired size
You don't just push on the 3/4" diameter when inserting , the bushing will close up (coke bottle sort of )
So your tool should have a .500 OD Pilot as well ...and have a chamfer at the beginning of the bore
The bushing then resizes when inserted and the pilot prevents it becoming undersize in Bore
Remember !!! it is elastic
In critical applications, Have a spare on hand and put the spare in a test hole FIRST... and measure your size change to know the correct bore size.
Rich

Electrojim
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Re: Need "Rule of Thumb" advice for Oilite bushings.

Post by Electrojim » Wed Jan 19, 2022 5:56 pm

Holy moly! All that makes very good sense, nice tutorial, thanks. Trouble is, I'll be looking for someone to do this job for me, beyond my pay grade. But at least I'll know the trouble the guy can get into and will discuss this beforehand. Nice tip on having a spare bushing; glad I ordered three!

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Re: Need "Rule of Thumb" advice for Oilite bushings.

Post by Conrad_R_Hoffman » Mon Jan 24, 2022 12:56 pm

A turntable bearing needs to have very small clearance. It runs at slow speed so getting a proper oil film to avoid metal to metal contact is difficult. IGUS bearings can be great, but the tolerance problem is near to impossible in a one-off situation. I'd do Oilite, but you will have to bore or ream it. Probably can't do that in-situ so next best thing is a drop-in piece. Maybe a thin wall tube with Oilite in each end, bored, reamed or honed to size, then held in the hole with some mild adhesive so you can get it out. Shellac or similar. The old AR turntables used a babbit sleeve that was sold commercially, but I don't know if that bearing company is still around. I don't know if you could pour a babbit bearing if the hole was made larger.
Conrad

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