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Drilling a 9/16" hole in ~2" thick rubber

bloomautomatic

Cast Iron
Joined
Oct 17, 2012
Location
Pennsylvania
We need to drill some 9/16" holes in rubber blocks that are about 2" thick.

These are part of an assembly and have to be drilled in place, horizontally. We have a mag drill with a regular chuck and one with 3/4" weldon chuck for slugger cutters.

We are using punches for the 1/2" thick material and they work well. They won't work for the thick stuff.

We tried a slugger cutter on it, but it gums up on the inside. Tried a forstner bit and it snapped off (I wasnt there so I'm not sure how they did it, may have been using a hand drill.)

A regular twist drill works on the 1/2" stuff, but it seems like its burning through more than cutting.

Due to the size of the it, I dont know that freezing is really an option.

Open to any ideas! Thanks.
 
Try a thin wall stainless "punch" drill, basically large hypodermic tubing with a sharp, conical edge that tapers from outside in. Run at low speeds with a bit of soapy (detergent) water to cool and lubricate the cutter.

For use with a mag drill, you might have to adopt a shank, if you can do this on a Bridgeport you can hold the tubing directly with a collet. You may have to dismount the drill to pull the core, or drive a sheetmetal screw into it and pull out.

Some distortion will occur as you go deeper, especially if you allow the drill edge to dull. A "outside-in" cone edge will tend to cut close to OD size, a "inside-out" edge will tend to cut small as the cone angle pushes material outward, which snaps back on drill removal.

Don't hurt yourself, a properly sharpened tube end is quite, uhh, sharp!
 
I'd look into avoiding having to do this. It's a loser.

But if I did have to do it, I'd try a spinning cutter that basically resembled a punch (a perfect circle, very sharp edge). It would also need a good relief for the plug to go into. Basically, a tube or pipe with a sharp end. And I'd use lots of lube.
 
I've had success cutting rubber with hole saws. Never 2" deep however.

Is it possible to melt it out with a heated piece of tubing?
 
If you can tolerate two ops, consider roughing it out 1/8" or more undersize, probably with a twist drill since you should not care too much about this hole other than its existence. Then go back with the sharpened tube for finishing.

2" is pretty deep, and the cone-shaped cutter is asking for a lot of deflection. Note that rubber is more incompressible than steel. It deforms much more easily, but do not confuse that for compressing. It still needs somewhere to go, and the volume of the cutter is displacing something somewhere. The end result is the central slug climbing its way up the middle, and all the internal stresses associated with that will ruin your size, finish, or heat treat if you let it go long enough.

On the other hand, with even a modestly-sized pilot hole there is a void for the displaced material to escape into, and you will be glad to have provided it.

Edit to add: The "safe" rule of thumb is to avoid 90% volume fill whenever possible, to account for rubber's high CTE compared to metals. So, size your pilot hole to remove at least the volume of the finish cutter + 10% of final size volume, but leave a bit of beef to slice off when you go back for it.
 
I have some tubing ordered to make the cutter. Your comments about having a pilot hole make sense.

We'll try them all out and see what works!

Thanks everyone.
 
Hole saw- grind out every two teeth or so to give the swarf a place to go. Run the saw slow so you cut the rubber and not grind it up. Peck the saw to get the swarf out, and use a lubricant- WD 40, soap water etc. If you burn and melt the rubber, it will win.
 
I have had really good luck drilling rubber with a forstner bit.
Might need to try it again, using some lube. I didn’t use any lube but I was only drilling 3/4” thick.
 
Depends on how hard the rubber is. There's a range of possibilities. If it's fairly hard try a 2-flute
slot drill. Run it pretty fast, WD-40 or something similar for lube, peck often.

We drilled a bunch of holes in some fairly thick rubber years ago and I know the above process
worked pretty well. The rubber was pretty hard but I have no idea what the durometer was...

Edit: Just remembered that you're talking about using a mag drill which probably limits your RPM.
I know we were turning the drill pretty fast. Wouldn't hurt to experiment, though. A new, sharp
slot drill would be best...
 
I have a fabric product that requires some 1" holes in the fabric. The 1" punch didn't work well.
So I went to Hazard Fraught and got the set of cheap hole saws. I took the 1" hole saw, ground off the teeth, then having only a drill press at the time, stuck the hole saw in the chuck, and a teardrop rotary burr in the vise, like a lathe, to bevel the inside. Works great on stack drilling fabric in an MDF fixture/clamp.
 








 
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