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Pressing Bronze Oilite Bearings into QCGB

evanthayer

Aluminum
Joined
Jun 13, 2018
Hi All,

I am attempting to press a new bronze bearing into the QCGB casting bore for the central shaft of my 1952 9A. I've pressed a number of bearings in but each has compressed past the required shaft OD clearance during installation, preventing central shaft insertion or rotation.

I measured the ID of the bore and the OD of the bearings and found this:

Bore ID = 0.7465
Bearing OD = 0.7525

I'm assuming the issue here is the interference fit? I've got 6 thou and I'm guessing it should be around 2 thou? Is the next step turning the OD of the bushing down by 3 - 4 thou? I don't have another lathe but I can finish the restoration and use it to turn the bushing down and install the QCGB later. What have other people done?

Thanks!

Evan

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Per BostBronze info in Boston Gear catalog, minimum would be .0015 press. Bore for your .7525 bearing would be less than .002 less - which it is far from since you say it is .7465

I fully expect SB made them an odd size so they could sell you the "proper size" bearings:D
 
johnoder said it right. Skip the std sizes-- machine oversize oilite to fit with .0005 to .001 press fit and install with loctite 680/690 retaining compound and you're good to go. Have machined several older QCGB units as such and they're running just fine . PM if you have a question about this process.
Johnny
 
When pressing bushings the ID will always be affected. Even if the bore was as clean as can be, and the entrance chamfered, it will shrink the ID some.

If you press crooked, bore has a ding, or you mushroom the bushing, it will be worse.

Where possible, I press the bushing, then bore it out, especially if I'm making it from scratch. Then the ID will be spot on.

Kinda hard to mount a qcgb in a lathe though :D. Might even be tricky clamping down if you have a mill.

If you're pulling bushing out to machine. . .The worst part for you is tightening the bushing in the jaws of a chuck without distorting it. It shrunk in a perfectly round bore. . .now imagine what your 3 or 4 jaw will do to it.

If you're only a couple thou off, I might consider leaving the bearings pressed in. And turn the shaft down a couple thou. Assuming you feel good the ID of bearing looks good and round as is, pressed in.
 
thanks guys for getting me on track. i'm going to turn down that bearing and then shove it (delicately) in with some loctite!
 
Is there anything special for turning down a bronze bearing/bushing ? Having never done one before & have always wondered if the machine work will cause the bearing/bushing to clog .
thanks
animal
 
Is there anything special for turning down a bronze bearing/bushing ? Having never done one before & have always wondered if the machine work will cause the bearing/bushing to clog .
thanks
animal

Same Boston Gear catalog cautions against negative rake tools that tend to CLOG pores in the Oilite
 
If it's solid bronze, no problem. If it's a sintered bronze, use the sharpest tools you've got to reduce smearing the surface. Positive rake is good, although maybe watch out for your particular bronze alloy being a bit grabby like copper. Insert like might not be high (doesn't matter if you just have one or two to do) but try one of the polished high-rake chipbreakers for aluminum, like Korloy AK or AR. If you have a cylindrical grinder or hone, you could leave a bit of excess material on the lathe and clean it up on the grinder/hone.
 
Evan and animal, I prefer using my Everede boring bars with adjustable carbide inserts; rough size the bore then I'll diamond grind to give fresh cutting edge and finish to size. Probably a little overkill, but it eliminates the smearing issue completely! Be sure to clean the oilite O.D. with Acetone. Have had issues with lacquer thinner in the past. Good luck
Johnny
 
Agree that Oilite is not a good choice for that bearing application. Oilite tends to cut un-hardened shafting and is difficult to machine properly. Oilite is called for where lubrication is difficult or sporadic. Since those bearings are (or should be) lubricated routinely there's no need to accept the negative aspects of oilite bearings.
 
The answer is YES. Oilite will remind you of cutting cast iron with the particles flying in your face & (btw--you will want to clean the scroll in your 3-jaw chuck afterwards 😉) ;
Solid bronze will cut somewhat like brass; minimal rake angle tooling helps control grabbing material. Definitely agree with above recommendations for solid if you have some available. Would also cut lubrication grooves in bore after properly sized to aid oil distribution
 
Typically in our shop we press in bushings then ream them afterward, if I were you I’d either buy the correct size reamer, or use an adjustable one and ream to size, I’d be a bit concerned with the bond of the loc-tite to the sintered bronze, which is most often impregnated with oil, another concern here is that the loc-tite May seal the surface of the bushing, preventing new oil from migrating through the bronze.
 
Honestly I’ve been going this way and that way in my head on how to get this done. I think your recommendation makes the most sense - I get a known strong fit (I’ve pressed in & out several bearings already) and a precision bore without over removing material.

The bearing’s current uncompressed ID is 0.626” which is the correct 0.0005” clearance on the 0.625” OD shaft. It fits well. I’ve just ordered an adjustable reamer (5/8” to 11/16”) so i can dial it in exactly (the 0.626” tap was 10 weeks out!)

I’ll report back.

Typically in our shop we press in bushings then ream them afterward, if I were you I’d either buy the correct size reamer, or use an adjustable one and ream to size, I’d be a bit concerned with the bond of the loc-tite to the sintered bronze, which is most often impregnated with oil, another concern here is that the loc-tite May seal the surface of the bushing, preventing new oil from migrating through the bronze.
 








 
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