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fitting (?) a shaft to new bronze plain bushings

Billy Boy

Hot Rolled
Joined
Jan 30, 2005
Location
San Francisco, CA
So, I've got my new wire/tubing bender more or less done, and I've pressed my sintered bronze plain bearing in place. They are held in place with a press fit as the holes are reamed to .749 and the od on the bushings was .7505.

Now when I try to slide my .625 shaft into place, there is interferance. I can press the shaft through the bronze bearings with no trouble, but I am unable to spin the shaft if i do this... even when I slip a sprocket/key over the end and grab the thing with a gloved hand, the shaft won't budge.

I've read alot recently about how acurate plain bronze bearings can be, so I'm wondering what to do here.

I figure the easiest thing would be to simply get a .625 reamer and size it up, but I just want to make sure that their isn't some other (better) approach.

Could I make a reamer by simply form realiving my shaft?

B
 
Reamers are generally not recommended because they "smear" the pores in the oilite and inhibit the lubrication process. You might try a soft broach ...

Make a steel shaft with a series of small steps, each one slightly longer than the length of your bronze bearing. The first step is the pilot and should be the same size as the existing bore. Successive steps are slightly larger - maybe just a few tenths (.0001) with the final diameter the size that you want the bearing bore.

Don't deburr the steps, leave those sharp corners. Press the soft broach through the bearing bore taking care to start the tool perpendicular to the bearing.

Good luck !
 
Maybe you could:
Measure the ID of the bushing.
Determine how much needs to be removed to get the clearance you want.
Press it out of what it's pressed into.
Chuck it in the lathe.
Measure the ID.
Remove the amount determined above using a sharp tool.
Press it back in place.

Roger
 
If you can chuck up the part holding the bushing, use fine sandpaper to just polish off .0005 to .001 on the id and see if that gives you enough. If you can't, chuck up the shaft and polish that up with sand paper.
 
I would try to turn the shaft using a little more leverage. I have fitted a few bushings by spinning a shaft close to the final size thru the bushings with a drill motor and lots of oil.
 
Thanks guys.

I desided that since this is going to be a very low rpm situation I'd risk the pores and ream the bushings with a piece of form realived shaft. Seems to be working well, and I can still see the pores.

Thanks again.

B
 
I've had this problem as well. Trouble is, the sintered bronze is so soft that when you make a "hard" interference like you did here, the bushing compresses and the ID no longer fits. Also, when pressing in the bushing, you'll likely deform the end you are pressing on, again reducing the ID.
Bronze bushings should not be a hard press fit.

Regards,

Benta.
 
The bushing's press fit is way too tight. That's why it was made .0005 oversize, to fit a nominal .750 bore with the proper press fit.
Oilite, or sintered bronze bushings just crush and collapse when fitted too tightly in a bore.
I'd ream it out to fit the shaft. All this hooey about not being able to machine oilite without messing up the pores of the metal is just that. It's done almost every day in most commercial shops with no detrimental effects, in fact most of the time while you're turning it, the stuff will throw oil all over you.
 
You can usually just take a precision fitting insturment (hammer) and carefully go around the shaft, tapping gently-to-medium hard in a radial direction, and it will help seat/clearance the two pieces.

You don't need no steenkin' reamers.
 
All this hooey about not being able to machine oilite without messing up the pores of the metal is just that.
Pete913, you may be right. However, I like to use procedures developed by the folks who design/manufacture the parts, in this case the oilite bearings.

The technique that I described in my post above is the one recommended by Boston Gear and is contained in the technical reference section of their bearing catalog.

BUT having said that, the engineering recommendations of the manufacturer are doubtless intended for maximum bearing life under way more stringent conditions than the one described by the OP.

Since Billy Boy's application is modest (VERY low speed and infrequent usage), his decision to ream that bore sounds like a practical one ...

I'll stick to the method recommended by Boston for my applications. I have four or five of the soft broaches I described, made over the years, for the most common sizes of small bearing bores. Didn't take long to make them and it takes only a few seconds to size the bores.
 








 
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