drilling holes in soft open-cell foam

Sounds as if you will need either a punch or you will have to burn them through the sponge (as with a heated probe, not flame!). The former method (IF you can find some good steel punches -- the kind with hollow centers and a sharp beveled ring) will probably be the best as the other tends to leave melted detrius around the holes.

Cookie Sewell

I think they use hollow punches with a sharp edge, compress the foam, then punch it. If you don't mind the mess (and the smell, which is really bad with polyurethane) you could heat up something metal of the diameter of the hole size you want you want and melt it through, although this will leave some goo on the inside of the foam. Don't get it too hot though; polyurethane will ignite and burn, and emits toxic smoke when it does.

Pat

I think this is the way to go

Yes, and I want to keep the cells open, while the burning, I imagine, would seal at least some of the cells.

Thank you for the ideas!

Leather working shop; they have them.

Pat

Here's another idea: My dad says that he used to make holes in foam rubber by soaking it in water (getting it full of water like a sponge does), freeze it, then drill a hole fairly quick right out of the freezer.

You'll have to wait a heckuva long time for the water to drain and for the foam to dry out afterwards

Hope this helps!

-andyh

This is a really cool idea. I have access to liquid nitrogen and to a

-80C kelvinator - so it should be a piece of cake... I guess.

It also leaves a nasty oily residue as the chemicals in the foam break down. You should be able to find a 1/4" punch fairly easily at a leather working shop, and possibly at a good-sized fabric or hobby store also. When you punch it, you probably want to do it on a piece of wood, so as not to dull the punch after it cuts through the foam.

Pat

Boy! Now that's a clever idea...somebody was thinking outside the box on that one.

You can dunk it in hot water after drilling it. That will melt out the ice. After that, just squeeze out the water like a sponge.

Pat

Watch out if you stick it in that; the warm water will make the liquid nitrogen boil, and you don't want to get splashed with that. I think the Kelvinator sounds a lot safer. I imagine you could dip the foam with no water in it into the liquid nitrogen and drill it after it was frozen, but something way in the back of my mind keeps saying that some odd chemical reactions may result from that... something associated with explosives.

You might want to take a piece of the dry foam and chill it down to -80 and see if that's drillable.

Pat

Freezing in a block of water and then milling is how aircraft honeycomb panels are shaped. The honeycomb structure is very fragile before it is skinned and this is the best way to create the required shape.

I tried the freeze-and-drill method, and it worked.

ummm..... and emits cyanide gas.....

wow. always cool to learn a new technique. now i gotta think of what i need it for.....

I mentioned the toxic fumes; that was found to be one of the leading causes of fatalities in airliner crashes as the passenger seats burned.

Pat

Freeze a fish and drill it before cooking, and you can serve holy mackerel.

Pat