I'm looking to do some machining (reducing the outside diameter) on some sintered bronze bushings to be used for bearings.
It's going to be light cuts, as the parts are small (10 mm diameter) and I can't clamp them, but will be holding them on a steel shaft made for the occasion, with a bolt through the bushing hole fixing it.
My question is: what geometry of the tool (HSS)? I've not been able to find references for sintered bronze. A bit of "trial and error" is possible, but it would be nice to start approximately right. My own guess is neutral rake like for brass, but…….
I think your guess would be fine so long as the OD is not the intended bearing surface. Seems I read a long time ago that if you're actually modifying the bearing surface itself then you want to use a very sharp high positive rake tool to keep from smearing the metal across the surface and closing off the oil pores (assuming when you say sintered that its an oil impregnated material). This shouldn't matter if you're modifying the OD such that it will press into your bore.
I recommend sharp carbide because I have found sintered bronze to be abrasive. HSS edges just don't hold up. I think the reason is hard copper-tin intermetallic particles in the sinter. I suggest either a brazed carbide tool that you sharpen yourself to a keen edge, or an insert with no "hone", which is the intentional "blunting" of the cutting edge often used to reduce chipping of the cutting edge. Since you are turning the OD, I wouldn't worry too much about closing the pores. I have heard of re-opening smeared pores, but don't know how it is done. I imagine you would have to de-oil and re-oil the bushings in doing so.
How do you "de-oil' a sintered bronze bushing?
I use em for all sorts of stuff that they were never intended to do, and I would love to know how to "de-oil" them.
I tried burning the oil out once and ended up with a tary mess.
Try soaking one in a solvent that will thin out the oil. Then put it in boiling water to get the rest of the oil out. Finally, heat it enough to get rid of the water.
Just don't use the best pot in the kitchen.
Take the coffee pot off the hot plate and put the bearing on the hot plate. Turned on of course. Every so often pick up the bearing and wipe the puddle of oil off the hot plate. Keep doing that until you pick up the bearing and there isn't any oil on the hot plate.
The reverse is true for putting oil into the bearing, except, you add oil to the puddle while the bearing is hot, then turn the hot plate off. The oil will wick into the bearing as it cools.
Thanks to Metlmunchr and Rklopp for good feedback.
Using the reference to "oil impregnated" to extend my Google search I hit pay dirt [img]smile.gif[/img]
The guess at the tool rake being neutral was right, and the tip to use a carbide tool is also right on.
Thanks for pointing me in the right direction, great forum, this!
Just to finish this one:
I did the OD machining, which actually was a nobrainer, cut was fine, basically you just get powder as residue. [img]smile.gif[/img]
The BIG problem was holding the workpiece... this stuff is so soft that it deforms permanently with just a little too much pressure (almost like lead). Junked 3 parts before I got the balance. Then, of course, you need to do really fine cuts, 'cause the workpiece is held so loosely.
In the end it worked.....