Cutters and speeds for styrofoam?

Instead of a hot wire, how about a hot thin strip of metal bent into the right shape ?

Cutting styrofoam does not leave a very smooth surface and is very messy.

Hi Tim: Extruded foam (not "beadboard") sands nicely and quite rapidly at fairly modest speeds. I used a 2" dia sanding drum, 80 grit, on a drill press at about 3000 rpm to sand a number of extruded-foam disks. With a cutter, the foam tends to tear at 3000 rpm, though higher speeds might do the trick.

Suggest getting a few scraps of foam from a nearby construction site and trying a few different mounted grinding stones; round, cone-shaped, etc.

Hope this helps -- P'rfesser

Oh, what a mess. I've been building with styrofoam panels (SIPs), so I know wherof I speak, as all the onsite cuts involved a circular saw and a chainsaw before we could get to trimming with the hot knife. Foam bits get everywhere, have lots of static tendencies, and head unerringly for air intakes on power tools. Avoid if at all possible, put in twice the suction you think you need if you decide to go this route. But I don't think you need to...unless this is more than a half-circle of bowl, or you need very high precision. Normal woodworking tools seem to cut the stuff fine at normal woodworking speeds - the carbide tipped circular saw blade tips would be doing about 200feet per second if my math is any good. Feed could be very fast when cutting without the OSB panel on the outside that I have.

With a stiffish "wire" (the formed cutter for inletting 2x8 into panel edges uses electric heating elements, similar to MSC bendable heating elements listed on page 4469 of thier catalog online) and a good fume extractor, bend the hot wire into a 12 inch diameter circle, or enough of a circle to suit your job. Might want to be 11-3/4 or 11-1/2 inches due to the way these thick "wires" cut/melt foam.

Plunge into the foam, turn 180 degrees, done. If plunging in makes too much of a defect, buy an ice cream scoop, study the scoop wiper mechanism, and replicate that to slice the hot wire though from face to face - but it's a trickier job than the first method.

If it is more than a half-circle, you could possibly make a "P or d" shape from the element if the opening is at least 6 inches, enter at an angle, pull to center, and rotate 360 degrees.

The metal band saw works great , smoother than from the factory. I think the hot "wire" will work if it is somewhat rectangular , but haven't tried it yet. Others into models use battery chargers and soldering irons with coat hangers. I know nothing of dead shorting stuff like this to cut foam, but I'm going to give it a try someday soon. I ran into a bunch of huge foam and want to cut leading edges for airfoils , the only other way for me would be to have 8' wire and jigs at both ends.

A friend told me IIRC 36 grit sand paper. 6 " isn't that big , what

12 inches. I would think if you could regulate it just hot enough so that it wouldn't distort if pushed too hard (turned in your case) it would work.

What if you made a tool like a wood ball covered with fiberglass resin or such and covered with sand and then spun it into the foam...

Hmmm, I don't know if I should say thank you or say your welcome.

If you don't mind making a simple jig, you can do this incrementally with a hotwire cutter.

The general idea is to make something like a hot wire flycutter having a "cutter" that might be a hotwire loop about the size of a spoon or even smaller. All you need is a cutting "tip".

You rotate both the work and the cutter, with the work oriented at 45 degrees as on a tilted rotary table. Maybe make a little rotating platform using a lazy susan bearing (just a couple of bux). If you have access to a large enough drillpress with a table that can both tilt and rotate, that would be ideal. My old Duracraft drillpress would almost do it, having 6-1/2" of depth from center of table to column.

The "flycutter" should have a radius of 4.243 inches. (That's 6 inches time cosine of 45 degrees.) It might just be a bent stiff steel rod with the small hotwire loop or U on the end. Only the end need do any cutting.

Line things up so the vertical "spindle" axis about which the hotwire flycutter rotates goes thru the center of what will be the spherical cavity. Then start rotating both the cutter and the workpiece, gradually lowering the cutter a bit after each rev of the workpiece and many revs of the "cutter". The cutter would be rotated by hand thru one rev and then back so you don't wind up the wires.

The cutter will take small bites as it and the workpiece are rotated. You will eventually reach a point where you'll have a hemispherical cavity of 6" radius. Final finish can be quite good if the work is rotated slowly with many revs of the cutter on the final pass.

I have not done this in styrofoam, but I have made spherical cavities in aluminum and delryn this way on a mill using a boring head.

SNIP

I did the same thing. Got any photos?

It may be necessary to form wire with increasing diameters. We have made some convex forms for fake carved stones using 14 gauge nichrome wire. There are several incarnations of hot wire cutters used for movie props on this web folder:

.

A tip about hot wire cutters is to use a foot switch to avoid the divets from the heat of the wire when cuts are stopped mid-cut.

Hope this helps

Rod Grantham

Ran into it again and keep forgetting. I think I mentioned it before , but...

I had a big piece of foam from a stereo or something under the planer and was intrigued when I cleaned up and thought it was a new type of packing and then realized that the stainless curled swarf was melting C shapes right though the foam and dropping on the ground.

So, you should be able to make up a hefty jig and heat it with a torch and go for it.

Found what your looking for and proves it can be done. Just don't know how to put the site on here. Go to Hot Wire Foam Factory

Thanks for the name -- I found their site and it has some interesting tools. We ended up buying some bendable tube heaters (1/4" diameter) and a temperature controller. I plan to make a D-shaped tool from the heater and rotate the foam block on a lazy-susan bearing to cut out the hemisphere.

Again, thanks to everyone who posted tips and suggestions!

(BTW the url for HW foam factory is

)

Sunworshipper wrote: