[bildoo]

I need to cut out a pocket in 40 durometer urethane rubber that is molded onto a roll. I make the aluminum roll and it gets sent out to get the urathane molded on. To save money in mold making (because there would be 35 different ones at $2000 each) we are trying to cut out a pocket on the outside diameter. Problem being, the rubber is so soft all it does is tear. I tried using a 2 flute finishing endmill and freezing the part to -6 degrees F. (in a regular household freezer) but that didn't work. To get the final outside diameter the rubber company grinds it to size. I was thinking on trying a small grinding stone from like a dremmel tool. I also was thinking on freezing the part in dry ice or liquid nitrogen?

Has anyone had any experiances with cutting or ginding such a material?

Ideas?
Tool type?
Endmill (diameter, helix, coating)
Grinding wheel (type, coarse, fine)
Surface speed?
Feed?
Depth of cut? (I'm guessing really small as to not apply too much cutting pressure)


Thanks

[amishx64]

Does / can the pocket go all the way down to the center where the aluminum rod is?

A quick sketch (side profiles) of what you are dealing with would be nice.

[bildoo]

No the pocket leaves the rubber. 125 thick. Also the rubber is only. 25 thick where there is no pocket.

[Dorsal]

If the rubber is porous, make a fixture to submerge the roll in water (maybe you'll want to vacuum the air out of it when replenish the volume of air with water) and FREEZE it. Then you can machine it easily until the ice melts.
If non-porous, you could still freeze it in a chamber filled with gaseous Nitrogen. Again, you'll need to work fast to keep it from thawing while you machine it.

[bildoo]

I am out of town today, when I get home tomorrow I will make a sketch of the part.

[amishx64]

No the pocket leaves the rubber. 125 thick. Also the rubber is only. 25 thick where there is no pocket.

Well that makes things a bit harder. I had an idea with a razor blade.

I like Dorsal's idea. If that doesn't work, you may consider using liquid oxygen. I don't think liquid nitrogen would be cheap enough, suitable for enough parts, or easy to get your hands on.

Liquid oxygen, on the other hand, is easy to come by. Those compressed air canisters have liquid oxygen inside. Tilt the can upside down and spray on the rubber and you may be able to freeze it close to the temp of liquid oxygen, -297.3°F (-183.0°C).

Careful though, the stuff causes instant frostbite and makes your skin itch for days.

[bildoo]

This is a section view. The rubber being on top (hatched area) the rest is the aluminum roll. The pocket does not go all the way to the end of the part.