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I need to cut 2x2 ft square pieces from a sheet of memory foam. Not sure what tool is best for this. Any ideas? In the future I'd like to cut circles and eventually sculpt irregular shapes, I don't know what tool can be used for this sort of job.

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3  
Time to invent the memory knife! –  Doresoom Aug 16 '11 at 3:22
    
I used to know this, but I forgot. –  Pete Becker May 16 '13 at 22:11

7 Answers 7

up vote 9 down vote accepted

For thicker pieces you might find you get better results by compressing the foam before cutting it. You could make a simple straight-line clamp out of a couple of 2x4s linked with a door hinge -- just put your foam in between, clamp the open end shut with a C-clamp, and use one edge of the wood as a guide for your cut. For your curved cuts it might make more sense to make a plywood die to match the final shape and press it down by hand or with something heavy before cutting around it.

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3  
Compressing first makes a ton of sense. I used to run a blinds franchise and had to cut honeycomb shades occasionally. Compressing then cutting resulted in near factory edges. –  Evil Elf Aug 16 '11 at 14:23
    
Thanks -- using this trick for honeycomb shades is an awesome idea too! –  Mike Powell Aug 16 '11 at 21:48
    
It is hard to visualize, could some one post a picture of how the setup looks like? –  haridsv Oct 1 '11 at 18:06

If this were styrofoam, I'd recommend a hot knife (basically a wire stretched taut on a frame similar to a jigsaw, and electrified to heat it). However, visco-elastic foam will behave differently and you probably don't want to be breathing in the fumes produces by melting it.

In this white paper from the Polyurethane Foam Association regarding visco-elastic ("memory") foam, the PFA states that most conventional tools including saws can be used to cut VEF. However, care must be taken to go slowly and not deform the foam too much with the cutting action, because the slower recovery of VEF to its original shape will cause defects in the kerf line and possibly cause the saw to bind more easily.

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a really sharp knife should do the trick.

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I used a sharp razor knife on my memory foam. You can make a line and just make long cuts. Do not try to cut through it all at once. Start by making your first cut deep enough that you can follow it through and make a straight cut. Just keep cutting down your line until you are through. Take your time and be careful and you will have a clean cut. Don't use a saw or hot knife you will just ruin your topper.

A razor knife is your best tool for this.

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2  
I was afraid this was the answer. It's what I do too, but it requires a steady hand and a ton of patience. I've yet to make a cut I was remotely pleased with. –  Steve Jackson Aug 16 '11 at 12:12
    
If you wanted, you could make you a mark with a chalkline or some straight edge to go by. Mine was not perfect either. But the sheets will cover it :). If you do not want to sell it the future, dont worry about it being too messy. It will still work the same. –  lazoDev Aug 16 '11 at 17:30

An electric fillet knife does great at cutting this stuff. Seriously. Give it a try if you have one.

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1  
Agreed (and I'm guessing so does Yitchak, who might not've realized they go by more than one name). It's that strange electrical appliance that you'd see in the 1970s for carving turkeys or roast. –  Joe Aug 29 '11 at 20:39

I use an electric carving knife. It works great.

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If you don't have an electric carving knife, which is the best tool, use a serrated bread knife. Same action on both.

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