DIY: Table Styrofoam Cutter
Trays holding meat you buy at the grocery store, egg cartons, shipping peanuts and hundreds of other commonplace items you use every day are made using Styrofoam, also knows as Expanded Polystyrene, or "EPS." You'll find EPS used to package electronic products and protect them from damage during shipment, yet surprisingly, EPS is also used in building construction. The large "Roman pillars" you see in front of a building often have a core of EPS that's coated with a chemical to seal it and add strength, then surrounded by concrete to give the column weather resistance and durability.
EPS can be cut into virtually any shape using a Styrofoam cutter. These cutters come in many designs ranging from computer-controlled cutters to table-style cutters. Here we're going to build a Styrofoam cutter table using resistive wire that gets very hot when an electrical current is passed though it.
First Considerations
Pressing a hot wire against Styrofoam causes it to melt. If the wire is sufficiently hot it makes a clean cut and tends to seal the tiny bubbles in the foam as it passes through. There are several kinds of wire generically known as resistance wire that can be used to cut Styrofoam. Nichrome 60 and Kanthal alloys are specifically designed to heat up to over 2000°F (nearly 1100°C), which is more than enough to do the job. In many cases a power supply of just ten to 20 volts (AC or DC) is sufficient to heat the wire to an orange glow. The best power supply is a variable transformer known as a Variac, because it allows you to set the current flow and thus the heat generated to just the right level. Batteries can be used, however at least a 12 volt battery and suitable means of adjusting the current flow are needed.
Nichrome 60 and Kanthal wires are available in a number of gauges that range from 16AWG to 32AWG (American Wire Gauge). These correspond to diameters of 0.0508 inches (1.29032mm) for 16AWG to 0.0050 inches (0.12700 mm) – the latter being roughly the thickness of five human hairs.
Thinner wires pose more electrical resistance per foot than thick wires, so choosing the right gauge wire to cut Styrofoam is important. Generally, wires between 20 and 32AWG work well.
Materials & Instructions
The fun of DIY projects is that you can use almost any material you have on hand to make this Styrofoam cutter.
1. The Styrofoam cutter is built upon a cutting table board. You can use laminated shelving material, plywood (smooth side up) or even Masonite or peg-board. Mount screw-on rubber feet at each corner on the bottom side of the cutting board so it doesn't slide as you push Styrofoam through the Nichrome wire. You may wish to draw parallel grid lines across the table to keep your work aligned as you work with different sizes of foam.
2. The guide block at the rear of the cutting board gives you a guide against which you can hold large pieces of foam, if necessary.
3. The L-bracket can be made from:
Wood. It has the advantage of being non-conductive, easy to work with and inexpensive.
PVC pipe with an elbow. Joining PVC pieces requires a primer and glue and may cost a few dollars more than wood.
In each case, the vertical dimension of the L-bracket determines the thickness of foam you can cut. The extension of the L-bracket limits the width of foam you can cut when pressing it against the guide board. Therefore, consider the sizes you expect to cut and size the cutting board and L-bracket accordingly.
NOTE: If you use wood or PVC to make your L-bracket and want a lot of vertical clearance – or a very long horizontal reach – you may want to build the bracket like this, with a tensioning wire supporting the horizontal arm.
You can mount the L-bracket to the guide board by drilling through the guide board and the L-bracket, then inserting a long machine screw with a wing nut at the rear of the L-bracket. This allows you to tilt the entire L-bracket to make angled cuts. A small dime store protractor can even be glued onto the rear of the guide board to "calibrate" the angle of tilt you choose. The "hole thru" in the cutting board allows the Nichrome wire to move freely as you tilt the L-bracket. Drill the initial hole (¼ inch drill bit), then tilt the drill forward and back to enlarge and lengthen the hole into a "slot."
Your power supply can be as simple as a 12 volt charger available in any retail electronics department. It should have a 1 Amp capacity or better. Alternately, you can use a model train transformer, which gives you variable voltage and, therefore, temperature control of the Nichrome wire.
Because Nichrome wire stretches as it heats up, use a small spring to attach the Nichrome to the L-bracket. The spring takes up the slack in the wire, keeping it taut as you cut your EPS foam. If you are using wood or PVC for the L-bracket, simply install a wood screw or self-tapping screw (or eye bolt) into the end of the bracket, then attach the spring to it.
The Nichrome wire can be attached beneath the cutting board with an eye bolt or screw. Pull the wire through the hole in the table, tight enough to stretch the spring to about half its length. Then wrap the wire several times around the screw or eye bolt.
Make sure your power source is OFF. Connect the leads from your power source using alligator clips directly to the Nichrome wire (not to the spring or screw) at the end of the L-bracket; and, at the connection point beneath the table. For a neat assembly, use electrical tape to hold the wires in place on the L-bracket. Beneath the table you can staple the power source wires to the bottom of the cutting table so they don't tangle or get in the way of your work.
Finally, to cut foam into circular or even conical shapes you can add a small piece with a nail driven through it and a guide at one end. Place the guide against the front of your table, then place the foam piece you wish to cut over the nail. Turn on power and slide the entire piece up to the hot wire. You can then rotate the foam around its center (the nail) to cut an almost perfect circular piece. By tilting the L-bracket you can cut conical pieces.
Conclusion
Building a Styrofoam cutter is a simple project that can often be done for about $10.00. A few pieces of found material, wood, PVC pipe, four rubber feet and miscellaneous fasteners – along with the Nichrome wire – are all it takes to build the cutter. Be sure your power supply heats the Nichrome wire to a point where it glows a dull orange. As you push foam through the hot wire, keep steady pressure on the piece. If you hold the foam stationary for too long you'll burn a circular hole rather than getting a clean, smooth cut.