Machining Pink Foam

[Carlo Urmy]

First of all, my apologies for asking a question that has been asked a million times before on a variety of different forums. I've actually done a fair amount of reading on this, both on this forum and on others, and have gotten some seemingly contradictory information.

Basically, I'm wondering about appropriate tools, feeds, and speeds, for machining pink insulation foam. From what I've read, I seem to be hearing two (seemingly contradictory) approaches. Some people are saying to use two-fluted upcutting bits (either standard helixes, or special foam cutting bits), at very very low rpms (5-8k), and feed rates around 6 ips. People advocating this approach generally warn about melting onto the bit, hence the low speeds and high feed rate. Other people seem to be recommending using four-fluted endmills, running at high rpms (15-20k) and moving between 6 and 10 ips. People advocating this approach seem to be mostly worried about finish surface, and don't mention melting as a problem, despite the higher flute count. Does anyone here have good experience cutting pink foam, and can help clarify this? I'm having touble knowing who to trust on this.

My other question is about pass depth. Is this a concern at all when cutting pink foam, or is the material so soft that you can run bits as deep as they will go? Does either shallow or deep cuts contribute to heat build-up in the cutting head? I'm using a relatively low-torque router on a shopbot gantry, if that matters.

Thanks in advance.

[Guy Hilliard]

Carlo;

Razor sharp 2 flute up spiral tooling is absolutely essential. 18K and 3 - 4 ips works for me.

Depth of cut is limited only by the flute length of the bit.

[Jerome Stanek]

1 or 2 flute upcut works well foam is very easy on the bit and easy to cut. you want a faster travel so it doesn't heat up and reweld.

[Jim Underwood]

I've been told by people that machine plastic that a faster feed rate is necessary in order to make chips rather than create heat and reweld (melt). So chip load calculations will help, but trial and error is really the only way to make sure you get it right. If you're melting the plastic, either your RPM is too high, or your feed rate is too slow. The acceptable range is much narrower than for wood.

[Dan Mullen]

I've cut alot of pink foam to use as forms for lost foam castings. I used a sharp 2 flute up cut bit and ran at about 30 ips feed. You can do a little fine sanding with a light touch if you need to touch up anything.

Dan