Press fit for bearing

[Furnace]

Could someone please tell me what would be a slight press fit for a bearing that has an .875 outside diameter. I need to bore a hole in a piece of 12L14 for this bearing and Im not sure how much to undersize this hole. If you cant tell Im new to all of this, so any help or sarcasm would be greatly appreciated.

[precisionworks]

.8741 to .8745 is the chart recommended sizing.

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Barry Milton

[darryl]

How are you measuring the bored hole? I only ask this because I had a bit of fun to start with when measuring a hole and expecting a good fit- to my horror the hole came out larger than I wanted despite me taking much care in boring it. That's when I learned that the dial indicator I used would read three thou small, with the hole therefore being three thou larger than indicated.

I don't know if this is a standard, but this slight overlap of the inside jaws prevents the thing jamming when you try to open it from fully closed. If this small overlap wasn't there, the inside jaws could 'pass' each other, preventing the caliper from opening.

If your final passes are to test fit something, you can take a few passes to remove small amounts of material each time, then test fit. Easy enough. But if the hole has to be a fixed size smaller than the thing that fits it, such as when needing a shrink fit of parts, or a press fit, then you'll have to be able to know exactly how large your bored hole is strictly by measurement. Do some experimenting on scrap to find out this difference in your indicator's reading between inside and outside measurements, and only then can you rely on it to tell you the true diameter of a bored hole.

Just thought I'd bring this up again for those who didn't know, or who have forgotten to factor this in.

[This message has been edited by darryl (edited 06-13-2005).]

[Evan]

For that sort of work I will make a plug guage from brass. I cut it with a taper of .001 over one inch. This allows easy measurement to .0001 based on how far the guage fits in the hole. Be careful not to jam it in the hole.

[Last Old Dog]

Darryl, is this bore measurement task a good job for inside mikes and a calibrated 0-1" outside mike? Or even a simple GO-NOGO gauge?



[This message has been edited by Last Old Dog (edited 06-13-2005).]

[JCHannum]

The dial caliper has it's limitations in measuring inside diameter.

Depending on the size of the hole, small hole gages or telescoping gages are your best bet. Get good ones, Starrett, B&S, Mitutoyo or Lufkin. Avoid the low priced imports.

They take a little practice to get the technique, but once mastered, very accurate readings can be made.

[Mike Burdick]

I think Evan brings out a good point here. Sure it’s nice to have just the “right” measuring instrument but - if not - one can make something very easily to do the job just as well – if not better!

[Furnace]

I have a set of the hole gages but theyre imports, the few times Ive tried them I didnt trust them. Im going to try the go-no-go gage and see if I can get it that way. This is a mount for a bearing for my little 7x14 cross-slide, in case any of you have tried it. Thanks for the help.

[JCHannum]

Loc-Tite products are the great equalizer in applications such as this. Especially in a lightly stressed installation as this, they can make life much easier.

A go-no go gage will only tell you if the hole is too large or too small, it will not tell you how much material to remove.

The tapered plug gage, if you can make one, will only tell you the diameter of the top of the hole, not if it is straight or tapered. It is also of little use in a shallow hole.

Get good tools and become proficient in their use. It is all part of the process.

[Evan]

It works for me JC. I have built a lot of projects using ball bearings that are a light press fit. After a while you end up with a handy set of plug gauges. If you do the boring right the top of the hole should be the same size as the middle. If it isn't then you have more basic problems to deal with first. For my designs through holes are the rule. It is pretty easy to come up with ways to retain the bearings. Stepped shafts and collars come to mind.