Cutting holes in foam

Hey dudes/dudettes.

I have a project where I need to make really nice clean holes about 90mm diameter by about 40mm deep in upholstery foam and was wondering if anyone has done this before.

I’m thinking maybe a holesaw which has had the teeth removed and then sharpened up might do the job…

Or is there another way? Who knows… stay tuned.

I once carved out a foam seat base off a 3d model by soaking the foam in water, freezing it overnight and running it on the CNC mill …

Typically, a foam converter will use a waterjet to cut such a hole.

If this is a DIY, get a steel-rule die made. It will cut the foam no problem. The die should cost more than $100.

If you are trying not to cut all the all through, that will be difficult. You could use the steel-rule die, cut through, trim to the proper length, glue back in place. Or center the steel-rule die so it can be placed in a drillpress chuck. Nick the edge of the die, use it as a drill. Compress the foam around the hole, remove the 40mm with a long-bladed box cutter.

Are the holes going all the way through?

I was thinking possibly something like this, making sure it was very sharp and at a very slow speed…

I’d recommend a combination of the above - soak it, freeze it flat and then use a metal cutting 3 1/2" hole saw (has tiny teeth rather than the demo hole saws with big knarly teeth) with a center guide bit on low speed to the depth you need.

I’d like to be there when you us try to cut a “grabby” material like foam with that fly-cutter … at a safe distance of course.

I’m thinkin’ hot-wire cutter? Maybe from a modified soldering iron/gun ?

See >

I have often seen household electric carving knives used in foam/upholstery shops - see video below.
Depending on diameter needed you could make your own foam hole cutter by sharpening edge of appropriate diameter metal pipe and a bench drill in this example.

Go to Clark Rubber and look at what they use. From memory the big one on Magill Rd near the Royal used an electric carving knife too.

Just to throw out another possibility, although the best approach really depends on the qualities of the specific foam you are working with, you might consider sharpening the mouth of a piece of steel piping and using that. With a softer metal like brass you can actually sharpen it by hand with an exacto, but steel you’ll likely need to use a lathe to cut a sharp edge.

I had to cut holes some ~10mm felt recently, and any conventional drill bit would not have worked because it would catch on the material. So I chucked up a steel pipe with a sharpened edge in the drill press and it worked quite well. This is also a good tool for cutting holes in something like foam core. You can also make cuts with it free hand, twisting it back and forth.

Of course if you aren’t going all the way through you’ll need to find a way to cleanly trim out the waste.

Note though you might need some kind of core in the pipe ‘bit’ you fashion, so that it isn’t deformed when you chuck it in the drill press.

The soak and freeze method sounds pretty cool, never heard of that!