Machining Rubber

[ctwo]

Friend wanted a bearing pocket machined into each end of some rubber bushings. I only had one snag and one tearout, but no lost parts. I went with a somewhat aggressive back rake on a small boring bar made from square HSS blank and sharp as I could go.

What is the general strategy? I was taking about 50 thou cuts at high speed. Too little would just push away and too much would get the rubber to split around the tool which could pull the rubber into the tool and cut in too deep.

[Harold_V]

Rubber cutting tools are available. They resemble the material used for making dies for punching gaskets.
Depending on the hardness, rubber is a real trial to machine. It responds very well to grinding, however. Use a small air grinder or a Dremel with a coarse wheel which you can shape according to your needs. That should work nicely.

H

[Bill Shields]

I have found that frozen rubber is easier to machine (quickly)...after you figure out the coefficient of thermal expansion.

Grinding is really the easiest way, if you have the facilities to do so.

You also want to wear a mask since you do NOT want to breathe the dust that is created...

[ctwo]

This guy is funny. He ran a machine shop (where I once worked) for ~25 years. He calls me up with a "very simple" lathe job...

The first one I tried, it snagged half way and pulled the part out of the chuck. The things were hard to hold because they were already hollow.

Thanks for all the tips and warning.

[warmstrong1955]

I haven't turned any rubber, but did do quite a bit of urethane tube. Not sure how it compares, but think it would be easier to work with than rubber.
A big collet would have been ideal to hold it I think, but I used my 6-jaw chuck.
I also did like you say, and sharpened some HSS with very aggressive rake, and sharp. A regular parting tool didn't work, too wide, and tended to rip & tear. I ended up grinding one that looked more like a knife blade.

I didn't try freezing any.....but I think I will if I ever do any more.

Bill

[SteveM]

Is there any way to adhere it to something to stiffen it up?

Either double stick tape or some adhesive that would release with temperature, water or solvent?

Steve

[rrnut-2]

I froze it to 50 deg below, but then we had a freezer that would do that. Sometimes I had to use dry ice to freeze it.

Jim B

[Harold_V]

I haven't turned any rubber, but did do quite a bit of urethane tube. Not sure how it compares, but think it would be easier to work with than rubber.

Depends on the hardness. I had a piece of food grade urethane that was too soft to machine----worse than rubber. The harder stuff? Oh, yeah! It works great.

Many years ago I owned a 24' Cruisers Gran Bateau. It was powered by a Chev 350 with a Mercruiser outdrive. The hydraulic trim cylinders were fitted with rubber bushings that extruded badly, and quickly. I got real tired of changing them out (at least once annually), so I made a full set of urethane. The originals were still fitted years later when the boat was sold. It's really nice stuff, and, hard enough, machines quite nicely.

H