Shaping rubber

I've successfully ground rubber on a lathe with a toolpost grinder. It's not fun at all. The rubber tends to grab (it's rubber, after all) and it helps to direct an air blast at the work to keep it cool.

I've heard you should freeze rubber before machining it. Obviously, it will warm up quickly, so work fast. If it were me, I might cut out the 1" circle of 1/2" rubber sheet using a hole saw with 5/16" pilot, then put this on a mandrel and freeze it on the mandrel, then pop it in the lathe and quickly turn your taper. Might work, you don't have much to lose. You can also use 5/16" threaded rod as a mandrel of sorts, face/center drill the ends, tighten the work onto the rod with nuts/washers, drive between centers with a lathe dog ..

GWE

This might be a job for a castable rubber.

Ken.

As has already been suggested, you can grind runner successfully.

If you're not concerned with sticking with rubber, you might consider using some urethane instead. If you get some that is hard enough, it machines quite nicely, and will outlast and outperform rubber.. You need sharp tools with considerable positive rake to machine it.

Harold

Rubber shaping is pretty easy with a high speed sanding disk. Even the softer materials will usually yield if you have patience. I used to fit a lot of rubber recoil pads to gun butts and an 8" disk loaded with

100 grit AO paper, spinning at 1750 RPM made sanding to 1/64" tolerances pretty easy with a little practice.

Randy

Chuck in a lathe if you have one or in a drill (press)that is secured to your bench with clamps. Get it spinning pretty fast and hold a running belt sander against it. When I raced RC cars on asphalt we used soft sponge rubber tire and thats how we trued them after mounting on the wheel. A coarse rasp or Surform plane works pretty good too.

Hockey pucks are machineable, and inexpensive.

Steve R.

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As already mentioned, the secret is getting the rubber cold. Dry ice in RV antifreeze can be applied with a squirt bottle or mister. Careful, the solution is so cold it will freeze burn you. I've used IPA in place of the antifreeze, but folks on this NG thought I was nuts as this can catch fire in theory.

Of course, razor sharp HSS tools with a huge positive rake, maybe 20 degrees, almost a super thick knife.

Karl

As has been stated there's several ways of doing this. The real question is how hard is the rubber. The harder the rubber the easier it will be to machine. If it's really soft rubber then freezing becomes the most desirable method. Preferably with something like dry ice (liquid nitrogen works but you need to be careful or it will cause the rubber to explode, BTDT). Harder rubber can be machined a little with a really sharp tool but will still be hard to get a good finish. The best method I've used on rubber is to sand it. I've used a disc sander to sand rubber vanes (made from conveyor belting) to size with good luck. The biggest problem is the huge mess. A shop vac in the right place helps but it's still a mess.

Wayne Cook Shamrock, TX

Seems a waste to use India Pale Ale....

The easiest way is to use a rotating knife to cut the rubber. It will shave off very nicely that way. Don't forget to relase any pressure on the rubber when you measure it or you will be measureing it wrong.

-- Why do penguins walk so far to get to their nesting grounds?

Certainly a waste to serve it that cold...

Mark Rand RTFM