machining rubber

and then drives

ll bits don't make

That's an awfully small hole. If it was any larger, I would make a hollow punch, like a leather or gasket punch,punch, and press it through the rubber.

Paul

then drives

don't make

Freeze it with liquid nitrogen, then drill the holes. You could try just putting it in the freeze depending on the type of rubber compound. or just wait a couple of weeks and put it outside. :)

John

When I was in industrial research, the strategy was to freeze it in liquid nitrogen. Then we could grind it. We were making drive pucks for experimental tape recorders. You had to work fast!

I've cut thinner sheet goods on the lathe using two sided tape, a round wood block in the chuck, and a blade in the tool post. The last time I had to size smaller holes I made a hollow punch and a carrier for the blank. The punch went in the tailstock chuck, slowly advanced it with the blank turning. Went well..

Grind your bit so it looks like a wood bit. I used to drill larger holes in rubber conveyor belt with a modified drill bit that looked like this.

LN2 comes to mind as the ideal "fixative". Cheap, too.

LLoyd

At the tire factory they machine rubber at room temperature by grinding. The "cutters" are like the carbide grit edge type, looks a metal grinding/sanding wheel. Try an abrasive type bit in a high speed spindle, like a Dremel tool or similar. The finish of a white wall and white letter tires is one of the results of this type of grinding. You do have to control the feed, perhaps some air to get the rubber dust clear. Our white sidewall buffers blow air while the grinders are down.

RogerN

Not with all that rampant Global Warming out there!

I have successfully machined rubber on the lathe by grinding with the tool post grinder. That's about the only thing that has worked reliably for me. For your application, how about putting a small grinding point in the Dremel?

Pete Stanaitis

----------------------

Wes wrote:

then drives

don't make

That's an awfully small hole. If it was any larger, I would make a hollow punch, like a leather or gasket punch,punch, and press it through the rubber.

Paul

------------------------------------------------- Here's something to consider.

Depending on the hardness of the rubber, it doesn't respond well to straight punching, but does quite well if you rotate the punch. To hold hole size, the punch should have a body size of the desired hole, with a hole bored, maybe ten thou wall thickness remaining. The cutting edge should be beveled towards the bore in this case, so the OD is the determining diameter. If the piece that is removed from the punch is the target piece, then the bevel should be the opposite direction, so the bore determines the size of the part. In that case, the bore should be the desired size, with the ten thou wall added to the OD. The cutting edge should be sharpened by spinning the cutter at high speed, applying fine stones to both the angle and the straight sides, alternately,until the wire edge has been eliminated. The cutting edge should be very sharp.

In use, spinning at a slow speed is adequate, and a little lubrication often helps. Depending on the rubber in question, you may use a light lubricant (kerosene) with success, assuming the material is oil resistant.

Cutting a clean hole is best accomplished by cutting into a piece of wood, or other soft material that won't readily dull the edge. I've used a piece of urethane with excellent results. Do a dry run with a stop set, so you barely break the surface of the pad on which you cut the rubber. The pad is best clamped in place, so the punch always hits the same spot. That way you don't damage the cutting edge by repeatedly hitting the bottom of the formed circle, and you get a clean cut. This work is best accomplished in a drop spindle mill (like a BP), but you can achieve reasonable success with a drill press, assuming you can slow down the spindle adequately.

Harold

This is the punch set chemists used to punch holes in cork and then rubber stoppers:

jsw

I'm wondering if a 3/16" paper drill bit would work? They have them as small as 1/8".

I found some more paper drills here, they have 5/32" and more styles to choose from, not sure if the Teflon coating would help or not.

I needed to make a counter sink for a 8-32 SHCS in 1/2" thick material.

Wes

-- "Additionally as a security officer, I carry a gun to protect government officials but my life isn't worth protecting at home in their eyes." Dick Anthony Heller

I'm curious if dry ice would be good enough? Somewhere I saw a design to make dry ice using compressed CO2. Wish I could find it now. We have CO2 for welding that I could tap.

Wes

-- "Additionally as a security officer, I carry a gun to protect government officials but my life isn't worth protecting at home in their eyes." Dick Anthony Heller

McMaster has some of those bits. Sadly, only by 16ths but I did order a few in my size range to try. Thanks.

Wes

-- "Additionally as a security officer, I carry a gun to protect government officials but my life isn't worth protecting at home in their eyes." Dick Anthony Heller

I guess you never chilled a six pack of beer with a co2 fire extinguisher. :)

John

then drives

don't make

A piece of stainless steel tubing used as a drill bit should work too. Sharpen the end by using a conical grinding burr on the inside of the tubing. This will work if the material is not too thick.

John