What size hole for press fit?

[jpowersny2]

Progress is going a little slower than hoped or anticipated, but that's alright. It's fun making parts twice .

The bearings that I'm using are 0.500 in diameter. I made a plate that accepts them. I used a 1/2" endmill. It's nearly a perfect fit...the keyword being "nearly". There is a very small amount of play that I'm not happy with. I'd rather press fit the bearings in so that there is no play at all. My plan is to make a new plate open up the recess by boring it on the lathe. But, what diameter should the recess be for a snug fit...steel into aluminum?

Here's what I have so far:

prev. thread: http://www.homemodelenginemachinist.com/index.php?topic=968.0

 

[Cedge]

Jpower
I'm not the expert on machining, but I'm pretty good at escaping from corners I sometimes find myself stuck in. It's possible you might be able to save the part with a trick I've used a few times. If the hole is only slightly oversized, I use what is called a dapping or doming tool to cheat it back to a smaller diameter.

$29.00 for a pretty nice set at Harbor freight and it has uses for contouring or doming metal as well.

The tool is placed over the hole and lightly tapped with a hammer. The lip shrinks a little which snugs things up a bit. Sort of like the idea of knurling a shaft to make it a little larger. This probably wouldn't work in a high stress application but our small engines are not heavy torque devices.

Steve

 

[mklotz]

There's a program (look for the FITS archive) on my page that will answer your question.
It uses the data from Tubal Cain's "Model Engineer's Handbook".

For a push fit, you want a hole size of 0.4997" for a 0.5000" bearing.

Unless you're fairly expert, hitting something that close will be difficult. I'd recommend reaming the hole to 0.5000" and then using Loctite.

Do yourself a favor and buy a bottle of Loctite 609 (IIRC) Press Fit Assist. Every shade tree machinist should have some. Clean the parts thoroughly with carb or brake cleaner before using it. It makes an astoundingly strong bond once it sets - your bearing will never work loose. (However, like many of these anaerobic adhesives, it can be freed by applying heat.)

 

[Cedge]

Marv
Ya gotta love Loctite. Blue for removables and red is for forever . LOL It doesn't let go until things get above 500° F.

Steve

 

[kellswaterri]

Hi Cedge,
the great ''BALL BEARING'' trick...my old Inspector would be spinning in his grave if he saw that one ... EX/ Air craft fitter,
All the best for now,
John.

 

[jpowersny2]

Wow! Excellent suggestions. I had thought about using epoxy, but decided against it. I hadn't considered loctite. As I am no expert, I really doubt I can hit 0.49997! I like Cedge's solution too. I have to think about this a little more.

 

[rake60]

Bearing press fits are pretty tricky on this scale.
For an industrial bearing I've always cut for .001 to .0015 press.
Cut a .500 -.0015" and you will be able to tap the bearing in, but it will exert enough
radial pressure on the bearing to load it up where it will not turn freely.

.0005" would be the maximum press. Or, .4995 diameter.
I certainly can't hit a tolerance that tight on MY home machines!
I cut for -.0015 then hand polish it to the finish size.

Rick

 

[mklotz]

Marv
Ya gotta love Loctite. Blue for removables and red is for forever . LOL It doesn't let go until things get above 500° F.

Steve

609, the stuff I recommended, is green. The red and blue stuff is more for screws, I think.

Also, I see I made a mistake in my post. I meant to say ream the hole to 0.501, the size one gets with an "over" reamer from an "over and under" reamer set. (Note to self: It's not sufficient to tell people to proofread their posts. One must do it oneself, as well.)

Everyone, not just newbies, should have a set of (fractional) over and under reamers in his arsenal.

 

[jpowersny2]

I don't know where to find the green stuff, but it sounds perfect:
http://tds.loctite.com/tds5/docs/609-EN.pdf
I'm going to get some.

 

[mklotz]

I don't know where to find the green stuff, but it sounds perfect:
http://tds.loctite.com/tds5/docs/609-EN.pdf
I'm going to get some.

McMaster Carr has it - I just checked - 10 ml for $11. Others may have it as well. Check an industrial supply house in your area.

 

[jpowersny2]

Ordered. Thanks. I've got other parts to make while I wait, which is a more productive use of my time then running around looking for it.