Question about sleeve "plain" bearings.

[DaffyJeffy]

Hi everyone. I'm primarily a woodworker so forgive this question which probably has an obvious answer. I've taken apart at least three different machines recently that all featured sleeve bearings (bushings) with oil-cups for lubrication. I don't understand how these work. Each time I drove the bushings out, I was expecting a hole in-line with the oil cup as a means to oil the shaft, but each time, to my surprise, the bushings didn't have a hole. Are the bushing (presumably bronze?) porous or something? Does the oil just get absorbed into the bushing or what? How does this work? I want to know because it's time to put some machinery back together and I want to do it right. THANKS!

 

[A_Pmech]

Although uncommon, it's possible the machine was built with sintered bronze bearings designed to be lubricated. Oilite bearings do not generally require lubrication as they receive a "lifetime" load of lubricant during manufacturing.

In standard practice, a journal bearing is lubricated by a drip or wick system which requires direct access to the journal surface through a hole in the bearing shell.

 

[rsanter]

Yes, they are porous and the oil soaks into them

Bob

 

[DaffyJeffy]

Thanks for the response. It seemed really strange to me that I observed the same scenario three times recently.

The first instance was a blower on my old furnace. I had been putting a few drops of oil in the cups every year. Finally I had to take the whole thing apart for a repair, and that's when I noticed that the bearing was soild, without a hole for oil to get to the shaft. I thought, "what a stupid design. All this time I'd been oiling these bushings and the oil can't even get to the shaft".

Then more recently I took apart two pillow blocks that support a 5/8" arbor on my shop. Same thing. No holes in the bushings under the oil cups.

Then I took apart a third machine, a small pully-driven grinder. Same Thing!!!

I thought, for sure I'm missing something here.

I guess when I replace the bushings (in the later two machines), I'll drill a hole through the bushings in-line with the oil cups.

 

[larry_g]

I guess when I replace the bushings (in the later two machines), I'll drill a hole through the bushings in-line with the oil cups.

How old/many years have the machines been running in this configuration? I suspect many years and they have had a long life. By drilling a hole in the bushing you will allow the oil to run through the bearing and leak out through shaft clearance in short time. Having a sintered (porous) bearing in there the oil will absorb into the bearing and release slowly as designed. I'd suggest you do a bit more research on this before re-engineering a system that has been proven to work well in millions of installations.

Now if your using a non-sintered bearing then you have to allow a pathway for the lube to get into the bearing/shaft interface. There are lots of different plain bearings out there and a proper way to lube lube them. Know what you have and then what is the proper lube to use in your application.

lg
no neat sig line

 

[DaffyJeffy]

All good info. Thanks. I'll take a look at what Mcmaster has. Are all bronze bearings porous?

 

[mtrcycldude]

If you are going to go to the trouble to oil it then put a hole in there. Bronze bushings are made soft to wear out without damaging the shaft. Bearing wears out and it gets replaced.
Some bronze is infused with oil (called oil-lite) but I have never heard of a porous bronze material.

 

[DaffyJeffy]

Very good point.

 

[rsanter]

Sintered ( not machined) bushings are all porous. If you drill a hole then the oil will run out quicker than you want. That's fine if you want to convert to using a grease zerk but otherwise leave it as it was. If anything you can use a small V file and file a small V groove around the outside of the bushing in line with the oil cup so the oil can get better distributed around the bushing

Bob

 

[larry_g]

.
Some bronze is infused with oil (called oil-lite) but I have never heard of a porous bronze material.

Oil-lite is a sintered (porous ) material.

lg
no neat sig line

 

[DaffyJeffy]

Thanks everyone for your knowledge and insights!

 

[marinusdees]

Sintered means a lot of small spheres and the oil fills the interspaces. Do not use detergent oils in the oil cup. The detergent eats the bronze. If it has oil cups, it is meant to be oiled. DOH.