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Bronze for bushings

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steamdave10/01/2019 20:32:18
495 forum posts
39 photos

I need to make a pair of bushings for a silver steel crankshaft which will rotate about 4 - 500 rpm.

I've got some bronze - drawn, I believe looking at the spiral marks on it. It's playing hell with the drills, just as bad as phosphor bronze: the hole seeming to close in on the drill and then the inevitable seizure. I could continue by boring, hoping to hit the correct size.

Regardless of technique, if I can machine it successfully will it in fact be good as a bearing material?

The Emerald Isle

Neil Wyatt10/01/2019 20:50:38
18899 forum posts
734 photos
80 articles

Should be fine, especially at such a modest speed.


Paul Lousick10/01/2019 20:58:46
1901 forum posts
673 photos

If used for a crankshaft, the hole should be finished by boring or reaming to ensure a running fit with the shaft. The finish with a drill is too rough and will not produce an accurate diameter hole.


steamdave10/01/2019 22:51:30
495 forum posts
39 photos

Shaft diameter is 1/2". The original intention was to drill 29/64, true up with a boring tool and finally ream.

With confirmation that the material is suitable, looks like I will be doing a bit more boring than originally anticipated!

The Emerald Isle

duncan webster11/01/2019 00:35:17
3710 forum posts
69 photos

Just bore it to size. Make a gauge a couple of thou small, when that will go in take very fine cuts until the crankshaft (or whatever) will go in.

John Olsen11/01/2019 04:03:57
1223 forum posts
92 photos
1 articles

Have you tried the dodge of taking the rake off the drill cutting edge? For turning bronze we use zero or negative rake tools, the same actually should apply to drills. What you do is stone away the spiral behind the cutting face. It doesn't take very much to make them stop grabbing. You don't need to touch the actual end of the drill.

Of course a drill you have treated like this is no longer quite so good for steel, although they will still work, however it is better to modify a drill that is kept separate for brass and bronze, preferably a few in a few desired sizes.

It could be LG2 bronze, which often comes with spiral marks on it. That is made and sold for making bearing bushes.


Edited By John Olsen on 11/01/2019 04:05:21

ChrisH11/01/2019 18:22:31
1009 forum posts
30 photos

Just set up 2" of Colphos 90 phosphor bronze in the 4 jaw to start making a new bearing bush for my lathe apron - don't ask why.

Got as far as drilling out and starting to bore the bush to fit a 5/8" dia shaft (which I also had to remake!). It drilled and is boring beautifully, speed about 400rpm cutting beautifully with no grab or seizure on any tool. Recommend it!


Ian S C12/01/2019 10:26:51
7468 forum posts
230 photos

About fifteen to twenty years ago one of the ?bronze bushes in the thread cutting gear box on my Taiwanese lathe failed, I had a bit of phosphor bronze hollow bar, and used that to make a new bush. It was bored on the lathe, no reamer was available, so it was fitted as bored.

Ian S C

Andrew Johnston12/01/2019 11:13:11
6407 forum posts
682 photos

The bronze will be fine for the application. Many bronzes have a tendency to grab drills; I use slow helix drills to start and then bore. I rarely ream; the last time was for my traction engine water pumps. Same as drilling, the material seems to close up slightly in that the reamer is very tight to turn by hand after reaming.. To get the water pumps rams to fit I had to grind them 3 tenths undersize. So either my secondhand reamer is fudged or the material closed up slightly.

I wouldn't bother with the reaming, just drill and bore. Measuring small bores accurately isn't simple. I usually make up a plug (or use a piece of the same silver steel as the crankshaft) and assess the fit once near to final size.


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