Machining rubber

[HuFlungDung]

Rubber machining requires a very sharp cutter, I know, but even this was not working satisfactorily in one job I took on. I was machining a lattice pattern something like a waffle iron, little squares created by machining a crisscross of channels in 2 axis.

There seems to be a "skin" on the top, even though the entire part was surfaced, so this would leave a heavy attached burr to the top edge of nearly every post: too much work to remove with an exacto knife, and too interrupted to use a shaviv deburring tool on. Oh, allright, I did have to deburr one entirely by hand

What I came up with was a heavy collar that was slipped over the body of the cutter, and setscrewed in position with only the exact amount of the cutter flutes exposed below, as I needed for the depth of cut. In this case I was using a 5/8 high helix 2 flute slot mill, and cutting .187" deep.

The collar serves to "hold down" the top of the rubber surface so it would cut, instead of being rolled ahead of the cutter. The cutting action reduced the chips to crumb instead of flakes, but by following the cutter with a vacuum, I was able to cut without stopping.

The plunge points I made beforehand without the collar on the cutter.

[castguy2003]

Neat Trick, I used to hate machining soft urethanes for similar reasons

[wjbzone]

I can tell you what not to try while machining rubber. I was trying to turn a rubber bushing down from a 2.5" OD to 2.4". The material was only deflecting and no cutting. (lots of smoke)

I decided to freeze the rubber. A little while in a freezer, did no good. I filled a tank with about 2" of liquid argon, and dropped the rubber in for about 5 minutes. I fished it out with a wire, and as soon as I touched it with a leather gloove. BAM!. The rubber shattered into hundreds of pieces. Glad I had on safety glasses.

Bill.

[HuFlungDung]

Thanks for the warning, Bill. I was thinking about something extreme like that

[wms]

HU,
I've used DRY ICE before to cool down some parts made of rubber, for machining and had good luck. Also used it to tumble rubber parts in the tumbler to deburr the edges. That also works pretty good.

I think liquid nitrogen or argon are, as Bill stated, way to cold. Something about stopping all the little electrons and neutrons

[wms]

Originally posted by wms I think liquid nitrogen or argon are, as Bill stated, way to cold. Something about stopping all the little electrons and neutrons

Mr. Science says:
Dry Ice temp = -112F (-80C for my Metric Freinds )
Liquid Nitrogen = -196F (-320.8C) Cold, cold, cold!

[Klox]

Years ago we had to machine a rubber component. We freezed it with liquid nitrogen and then machined it. It worked! Maybe we did something right? We did not have a explosion like wjbzone described. Very interesting.....

See you guys
Klox

[CAMmando]

Havent machined a whole lot of rubber, but U have frozen it (dry ice) and also ground it at room temperature. When the application permits, grinding works pretty well.

[CHIPPER]

I'll 2nd that about grinding it, I often have to enlarge the I.D. of cuttlass bearings that have a very soft rubber insert in them and after trying many different methods, mounting a coarse stone on a tool post grinder works like a charm, leaves no burrs at all and a very smooth finish, a little coolant keeps down on the smoke produced.

[sorincnc]

Had to do some machining on rubber sheet (about 1/16 thick. Not having much success, I tried using a diamond bit (just like dremell sales). Used with very high RPM (10K spindle) the bit actually was grinding through the ruberr and worked great. I had some problems with the heat first but turning the coolant took care of that. If your machine doesn't have flod cooland you might want to try one of these cold air guns . They work extremely well when in need for really cold air or when coolant use is not allowed or available. They go for about $150 but are worth their weight in gold when you need one (I also machine lots of specialty plastics that might be afected by the use of coolant.
Regards,
Sorin

[cleve]

Thanks to everyone for the come back, reguarding the mechining of rubber. This is a great site. I just recievd my first mill, it is a trak DPM SX2 w/ prog. spindle. Im in the learning curve. Thanks
Cleve.