Boring a Bronze Oilite Bushing

[snub]

This is more of a 'can I' question, as opposed to a 'how do I'. I wish to take an oilite bushing and bore the i.d. to fit a shaft I have that is an odd size. I have heard that doing this will close the pores in the bushing and it won't release the oil properly. Is this true? This is for a shaft that will be turning 30 RPM.

I was wanting to use a needle roller bearing, but the shaft has an o.d. of 13.93 mm. So a 14mm bearing would be sloppy. Perhaps there is some way I could increase the diameter of the shaft with some shim stock?  All comments and suggestions are appreciated.

[arnoldb]

Hi Snub

I'm not sure about the bushing and how it will behave - but at 30 RPM I don't think it will be much of a problem...

If you have a knurling tool and don't mind working on the shaft, a light knurl where the bearing must go should do the job to increase the size the small bit that's needed to use the bearing though.

 , Arnold

[Stilldrillin]

In a previous life, long ago. I used to machine oilite, regularly.....

Don't remember any special instructions....... 

David D

[Ned Ludd]

Hi Arnold,
I hope I misread your suggestion to knurl a shaft to make a bearing surface for a needle roller. You knurl a surface, if really positively absolutely have to, to make a shaft bigger to fit the inner track of a bearing, not a needle roller. A needle roller has no inner track and uses the shaft itself as a bearing surface.
Ned

[snub]

 ^  I thought that too, but I did find a company that sells miniature roller bearings that have a sleeve on the inside:









On third thought, I could probably machine a bushing for the shaft to take it up to 16mm.

[Lew_Merrick_PE]

Hey Snub,

1) There should be some clearance between a shaft and bushing.  This is called a Running Clearance -- something you can look up in Machinery's Handbook.  If your shaft is ø13.93 mm and your bore is ø14 mm, then your clearance is 0.07 mm (i.e. .0028 inches).  You really only need to cut that in half to get a good running fit.

2) There is no problem cutting oillite bronze so long as you use sharp tools.  The warnings you hear are really for dull tools that will "mush over" the pores.

3) One solution would be to knurl the shaft and then turn it down to very slightly oversize and finish it to size using abrasives (which will round the "corners" of the knurl to keep them from digging into your bushing).  Another solution would be to turn down the diameter slightly (say 1.5/1 mm or so for a nominal ø14 mm), press on a sleeve, and machine the sleeve to the desired size.

When I began my apprenticeship, I asked Herr Meister Muller the difference between an apprentice, a journeyman, and a master.  His reply was, "An apprentice, he makes a mistake and knows not what to do.  A journeyman, he makes a mistake and can repair it.  A master, he sees the mistake before he makes it and avoids it."  (A) I have yet to find a better definition set than this; and (B) after more than 40 years, I am still only a journeyman...

[arnoldb]

Hi Arnold,
I hope I misread your suggestion to knurl a shaft to make a bearing surface for a needle roller. You knurl a surface, if really positively absolutely have to, to make a shaft bigger to fit the inner track of a bearing, not a needle roller. A needle roller has no inner track and uses the shaft itself as a bearing surface.
Ned

Hanging my head in shame - Ned's absopositively right.  I missed the reference to needle rollers , and knurling the shaft won't work for that - thanks Ned! - it will only work for a fixed inner race.

 , Arnold

[Ned Ludd]

Hi Arnold,
No need to hang head, it happens to everyone, you see something and read another. It does show how useful these forums are, if one chap drops a minor bo**ock,  there are others who will jump in and point out where the info is suspect, and yet more who will come up with a better idea.
Ned