question on big box blue foam sheets...

[rbarrow]

I bought a 2" sheet of blue insulation foam from a big box store for some 3D prototyping. I have tried 100 combinations of bits and RPM to get a clean cut (like I see on a few other posts here) but all I get is a ragged edge melty look.

I know that high rpm and flute count are typically the combination for this stuff but I am beginning to wonder if I have bought the wrong stuff (although this is all I see they have).

This stuff has a plastic film on it as well that I peel off...if that help ID it.

Am I using the right stuff? Don't see any pink foam or I would check it out.

Roy

[billp]

Roy,
Are you using a ball nosed bit for these cuts?

[rbarrow]

Both em & ballnose. Running between 15-18k rpm. I guess I want it to cut like HDU which I know it won't.

[steve_g]

Roy

See last page of this document.

SG

http://www.talkshopbot.com/forum/showthread.php?t=15176

[rbarrow]

Interesting!

Slow & conventional. A combo I had not tried.

Thanks for pointing me to that excellent piece of work Steve!

[Brady Watson]

It seems that they have changed the 'formula' on the blue & pink sheets as of late. They are not the same as they were in years gone by - R-value has gone up and machinability has gone down. The new 'pink' boards I have seen are much darker in color than the bright Owens pink color, and they DO MELT quite easily - and load up the bit with styro-taffy...

Depending on the brand you get, styro may no longer be the beginner's best friend...

-B

[steve_g]

It seems that they have changed the 'formula'

Anyone

Do the speeds given in the "Router Bit Basics" article I directed Roy to still work? Do I need to Up date the document?

SG

[rbarrow]

Brady...
That was my first thought...something has changed. I used some old blue foam many years ago and I recalled it machining a lot better than what I just bought. Didn't try the slow speed conventional cut however....

I was just trying something inexpensive and quick to prototype some 3D stuff...and

[propellers]

Roy, We commonly use foam to proof our programs before cutting the actual part. Home Depot carries pink foam, Lowes blue and green, we do not use the green due to the plastic covering and its expensive compared to the other two colors. The density is the same on both foams and they are both PolyStyrene and cut identical.

We use a Bosh flat bottom 1/2" two flute srtaight bit purchased at Lowes. The best results for us is 10,000 rpm and feed rates 1.8 - 2.1. Our depth of cut is .25" - .5".

[rbarrow]

Been a while Lonnie! Thanks for the tip on speed/cutter...I'll see if that gives me what I am looking for.

Roy