Adjustable Hotwire Foam Cutter With Fence

Initially starting with Creativeman’s Mighty Goliath I decided to create a foam cutter that was adjustable for various angles, had a fence to facilitate straight cuts, made removal and installation of the hotwire easy, and folded for taking less space when stored. Additionally, I wanted the table to be an element unto itself – the idea was to use a battery charger as my transformer, along with a separate control box and foot pedal (that are used in other projects) so that I would not have to have a single power source and controller for the three tools I use them with.

Step 1: The Table

1. As pictures explain quite a bit I won’t go into to details of the construction but I will point out a few of my reasons for building it the way I did. For those not familiar with hotwire cutters there are several other folks with instructables that explain the theory and even include electrical diagrams. I am no electrician (although I have been known to provide them with employment if not entertainment) but a basic knowledge of wiring is all I needed for this project.  For the table (please excuse the Jackson Pollack design – I reused my children’s design table which I painted this way to hide their messes - if you can’t beat ‘em join ‘em) I decided that a round shape would give me more space and made it easier to place my fence at any location in regards to the wire. The elongated slot gives enough room for the wire when the arm is rotated and is probably wider than it needs to be. Four legs form the base and the arm is made from three separate wood pieces, two horizontal and one vertical. At the pivoting section of the arm, provided by a 6 inch bolt, there is enough friction between the two wood pieces to hold the arm tightly without shifting. The fence is just a smooth piece of rectangular aluminum and has a small bolt at one end with a round wood washer to clamp or pinch the table to hold it tight. At the other end I use a cheap plastic spring clamp since it is easy to place at any point on the length of the fence.

Step 2: Arms

1.A small spring at the top of the arm puts some pressure on the wire and will take up slack as the wire heats up – I use #10 guitar string and also bought #12, 14 and 16. This #10 cuts well even with multiple layers (up to 4 inches thick) so I haven’t tried anything else. The wire arm is adjustable past 45 degrees however you have to keep in mind that you must cut in-line or parallel to the axis of the arm – meaning the fence has to be parallel to the bolt on which the arm rotates to have a true 45 degree cut. I put witness marks in ink on the back of the lower support that the vertical arm is bolted to. The lower attachment is a smooth shank bolt, screwed into the lower vertical arm that the wire wraps around and continues over to a small cable clamp. The clamp makes it easy to adjust the tension of the wire and bolt gives the wire something smooth to curve around and provides good contact for electricity.  The lead is attached with a small bolt to the head of the smooth shank bolt after drilling and tapping it. I attached it to that instead of the aluminum bar as the bolt is not tightened down and doesn’t have good electrical contact to the bar – again it’s purpose is to give the wire a smooth radius to pull around as it goes to the clamp. This bolt should be on the same axis of the adjustable arm but even if it isn’t the spring on the top arm will stretch to compensate for the wire being pulled tighter when you reposition the arm.  

Step 3: Battery Charger Connections

1. Two bolts at the ends of the leads (white wires that follow the two horizontal arms) are where the leads for my battery charger are attached. This is the same spot you could attach your configuration of a power supply and control box (transformer and dimmer switch for example).

Step 4: The Box

1. This old wine box is the most useful part (to me anyway) of this system. I have two other tools in which I use this box - a chestnut roaster made out of an old washing machine and an old hair dryer that is used on a metal melting blast furnace. Both systems require that I adjust the voltage to them to modify their speed – since I only had one switch (used to control an old ventilation system) I needed it to be interchangeable between my uses. My battery charger also sees double duty for de-rusting metal parts (i.e. electrolysis). Sometimes I even use it to charge batteries. In any case I didn’t want to dedicate these tools to any one use. Hence, I created “the box”. Basically it has two outlets (in Italy they have 4 different types of plugs – no one agrees on anything here) so I had to make it adaptable to various plugs. It has an on/off switch and a separate variable speed switch. The typical dimmer switch (found in Home Depot) incorporates both of these (push on/off and turn to vary the voltage) although they might not have the same amp/voltage rating.  The three pronged plug (old phone system connection) goes to my foot pedal.

Step 5: Foot Pedal

1.  A very beneficial addition to any hotwire system is a foot pedal – credit for this idea goes to this website; http://www.horrorseek.com/home/halloween/wolfstone/HalloweenTech/fotmak_MakingFoamTools.html - I got some great information from these folks. For any of you working with foam I highly recommend a foot pedal, I cannot emphasize just how handy it is. For the pedal to work I have a light switch (common in older Italian homes) that is a simple spring contact switch – push and hold to turn it on. To disconnect the pedal from the rest of the system I used an old lever-type switch (see inside box in previous step) that my grandfather had amongst his bits and pieces collected over many years in refrigeration (Depression Era folks didn’t throw anything away, luckily for me). When the switch is closed electricity flows through it but when open electricity can only pass through the foot pedal. A regular plug could be used in place of my three-pronged telephone plug, but I wanted something that couldn’t be accidently plugged into with anything else. Again, I am not an electrician and am not including any schematics here.  A basic idea of wiring is all I used and you would need to adapt your materials to your use. My stuff is a bit different as I live in Italy.

Step 6:

1. This is how the system looks when connected. The battery charger is plugged into the box and the box is plugged into a regular wall outlet. The foot pedal is plugged into the box and the lever switch inside the box is opened. The leads to the battery charger are connected to the bolts on the arms of the cut table, and I am set. Before actually cutting any pieces I make a few test cuts to make sure the wire isn’t too hot for the type and thickness of foam I am cutting. As far as storage, with the wire loosened from the cable clamp and the arm resting all the way down against the table this table (hanging vertically) takes up about 6 inches of wall space. 
I welcome any corrections, comments, or alternate ideas!