Vol. 16: 5-Minute Foam Factory

Cut 3D shapes out of styrofoam.

By Bob Knetzger

Photos by Garry McLeod, Bob Knetzger

Illustrations by Bill Oetinger

+ Downloads & Extras:

Conic Sections

Combine a raised and angled stand with a circle-cutting action and you can cut cones!

Spin the foam around the angled axis and you'll cut a cylinder with an angled edge - a cone.

Surfaces of Revolution

Cut compound curved surfaces with a straight wire! A cone cutter with an offset axis will create a "hyperboloid of revolution" - the same shape as a power station cooling tower. Use an angled pin as with the cone, but position it so that its axis and the cutting wire are skew lines: nonintersecting lines in different planes.

Spin the foam carefully around the pin. The angled axis will cut a twisted shape. You'll have to break apart the surrounding ring of foam to free your part. Try various angles and distances between the pin and the wire to make gently or tightly curved shapes in different sizes.


For perfect results with complex shapes, make a cardboard template to use as sort of "slide guide." Cut your shape out of thin cardboard, then pin it or tape it with double-sided tape to the foam.

Slide the hot wire along the edge of the template as you cut the foam.

You'll get a smooth and accurate cut. If you happen to stray wide of the edge, just go back and cut again. Use the template over and over for identical perfect parts.


Picture Cutouts and Silhouettes

Here's a single-cut project that makes a fun silhouette or cutout paper doll figure. Print out a picture of a figure on label stock. Carefully cut out the figure from the background.

Peel and stick it to a piece of EPS foam (a black meat tray looks cool!).

Then use the paper figure cutout as a slide guide as you cut.

Make a notch at the bottom and add a small stand - makes a fun stand up figure!

Picnic Plate Planes

Make a glider from a sytrofoam plate. Cut a swept-wing slide guide pattern from a piece of chipboard.

I've also included a shape that will make a separate tail fin. Slightly bend the pattern to conform to the dished shape of the plate, double-back tape it in place, and then cut with the hot wire.

The final cut piece has up-curved wingtips thanks to the plate's shape. Cut slits to join the fin and body. Also cut some slits in the trailing edge of the wings to make ailerons; bend them up to adjust for more lift. Tape on a penny for a nose weight and give it a toss -watch it glide!

Use the slide guide over and over to make an entire squadron of gliders from picnic trash.

Identical Snowflakes

Cut a stack of foam pieces to make a bunch of identical parts all at once. Make a snowflake template by folding a 6"-diameter chipboard circle into sixths, then cutting out your design. Leave the folded edges uncut; that way there'll be no closed "holes" in your snowflake design.

Unfold the template and pin it to a stack of styrofoam picnic plates.

Carefully cut along the guide to make a stack of identical snowflakes. Make some small slits at the outside edge of the snowflakes.

You can connect them slot-to-slot to build a snowflake sculpture.

You can also make multiples of various thicknesses. First cut the profile shape, then turn the part on its side and use the fence to cut thick or thin slices, like a deli meat slicer. I cut a skull shape, and then cut slices to create skull-shaped decorations.

TIP: To cut a "doughnut hole," just poke a small pilot hole through the foam with a pencil. Then unhook the nichrome wire from the rod, thread the wire through the poked hole, and reconnect the loop over the notch. Turn on the hot wire and cut the hole!

Double- and Triple-Cut 3D Shapes

Create a 3D shape by making 2 cuts at 90° to each other. First, draw matching front and side views of a three-dimensional shape.

Use the guide fence to square up a block of foam, then carefully tape your front- and side-view templates to the block. Be careful to line the views up.

Now make the top-view cut. (I've temporarily removed the shape to show the result of the first cut.)

Leave the shape inside the cut-off block. Turn the block on its side and make the side-view cut. When you remove all the cut-off parts, you'll have a sculpted shape.

This exploded view shows the bear shape surrounded by some of its cut-off parts.

You can also make shapes with 3 views for even more details. Check out this mini "dart" glider, complete with hook for launching with a rubber band!

It was created by making 3 cuts, using top-, side-, and front-view shapes as guides. When making a 3-axis part, remember to keep all the parts together in a block as you cut. This helps keeps the x-, y-, and z-axis cuts at a consistent 90°.

Adapt these cutting techniques to fit your project, whether it's functional boat hulls, custom-shaped insulators, or fanciful decorations.

Now ... what will you make with your hot wire foam cutter?

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