Posted by bpfink on September 10, 1999 at 09:37:57:

In Reply to: Where to find foam? posted by Uudam on September 09, 1999 at 14:43:29:

Using foam as the pre casting or form media can have major advantages in lower costs and workability. Like any other media though it has it's pluses and minuses.

There are many types of foam but basically two you will find most usable.

Both can be gotten at most lumberyards since they are sold as sheet insulation. Both come in various thickness and sizes from 2 x 8 ft sheets to 4 x 8 ft sheets (plus some others).

Urethane foam is generally a tan / yellow color and can be worked with razor sharp knives or wood working saws but really NOT with hot wires or heat cutters. The dust from ANY foam is a bad thing so lungs must be protected and later floor dust from them will last a long time so it has to be collected, discarded and eliminated. Urethane foam will not break down much with paints or fiberglas (polyester resin) coatings so it is used sometimes also the basic form for surfboards or small boats, etc.

I don't use this very often, just if the need arises.

I never use it for a hot metal poured on burnout system. It does NOT burnout well that way at all.

I have used it for either direct modeling where a rubber mold is to be taken off of it, or when the burnout is to be a conventional 3 to 7 day lost wax investment burnout at up to 900 degree F.

The Styrofoam used most is gotten in sheets from 1/2 inch thick on up to 12 inch thick blocks. This also comes in many different densities and closed pore sizes so carving it is different with each. It can also be so dense you can nail into it if you get the heavier roof covering type. Fine pore sizes can be carved, sanded and shaped to a high degree of control and I usually start out by cutting it into basic sizes on a table saw with a course blade. Again, collect any dust and discard... I do that by having it vacuum sucked and blown right from the enclosed saw and into a steel drum OUTSIDE and covered with a very fine stainless steel screen lid (like on a gas line filter but a whole sheet) and then adding a few cups of gasoline or lacquer thinner which then quickly turns it into a thick paste. This is obviously dangerous as you are dealing with several potential problems:

#1 dust (of any type)

#2 plastic that will not breakdown if inhaled

#3 gasoline or thinners

so all precautions must be taken when using wood working tooling on the plastic. The resulting paste dries to a hard skim pad like the pancakes mother used to make and we throw them out same way also.

An alternative is shaping with a hot wire or hot knife and there then is no dust. Of course the fumes given off are poisonous so you still have to be careful and vent real well (like outside or in front of a large exhaust fan).

Hope this is a start.

The kind of foam that coffee cups are sometimes made from (with the fine beads stuck together) is also available in sheets but is NOT one we use. It works but has little control when detailing or shaping to a specific need.

There are other posts here on artmetal regarding the uses of foams so check around here. Nearly everyone has something new to add to the usage and safety. A section down the list Casting Forum list (Bramyak1) labelled FOAM SCULPTURE may help also.

bpfink

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