Foam Cutter Setup
Here is a simple, inexpensive, safe foam cutter you can make and use that really works. By Lee Aston
THIS IS MY CUTTING SYSTEM
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POWER SUPPLY ASSEMBLY - See the attached schematic of the foam cutter.
1. THE POWER CORD. Cut the female plug off of a 3 wire extension cord (with ground). Leave the male plug and at least 4 feet of wire.
2. THE GFI. Expose 4 inches of the internal wires and strip 5/8 inch on all three wires; connect to the power source side of a GFI outlet. The small side of the plug goes to the hot connection, and the large side of the plug goes to the common. Make sure the ground is also connected. The GFI will not cut the power to the bow from the transformer but it will cut the power inside the power supply and to the transformer. Use an outlet power checker to make sure you wired it correctly.
3. THE DIMMER ON/OFF SWITCH. The dimmer is both the power control and one of the two on/off switches in the circuit. The dimmer will have three wires in most cases, two black and one green. The hot side line out (or load) of the GFI is connected to one of the dimmer's black wires. The other black wire goes to the hot side of a regular wall outlet (the small slot side). The green wire connects back to the ground connection on the GFI outlet. I have built 3 of the power supplies as described and have found I like the slider version of the dimmer switch better than the rotary version. The slider version is the same shape as the GFI and a square face outlet can also be used to make the final product look better and fit under a readily available triple switch plate or outlet cover.
4. FUSES. It has been recommended that a fuse be place both between the dimmer on/off switch and the transformer and between the transformer and the cutting bow. I have not used fuses in my present power supplies but would like to pass along this safety idea.
5. THE WALL OUTLET. The household outlet will be controlled by the dimmer along with the transformer. The hot side (or small plug side) of the outlet is connected to the second black wire from the dimmer on/off switch. The common wire from the load side of the GFI will attach to the common wire side (or large plug side) of the outlet. Connect a wire from outlet ground back to the ground on the GFI. I plug a 40 watt bulb that is in a two prong plug adapter in this outlet to let me know that the power is on and if the power is reduced by the dimmer.
6. THE TRANSFORMER. A 24-volt 3-5 amp transformer is preferred. The 120-volt connections on the transformer are connected to both sides of the wall outlet. Use the screws on the wall outlet for easy connections. You might have to solder wires to the transformer connection points. When you mount the transformer on its wood base, make sure you install a ground wire from the frame of the transformer back to the GFI ground. Silicone any exposed wires or connections to prevent accidental contact. Sources for the transformer are listed at the end of the instructions.
7. THE CUTTING BOW. The bow is made from a 1" x 4" x 54" pine board. I drilled a 3/8" hole at 90 degrees two inches in from each end. In each of these holes, I gently tap in a 12" landscape spike that is sold at local hardware stores. Do not slant the spikes, because if you slant the spikes, the rubber bands tend to slide up the bow as it is being used. Longer bows can be made as needed. It only costs about $5.00 to make a bow. I have five different bows all for different purposes.
8. THE BOW SUSPENSION. The bow is suspended by a nylon cord tied through two holes in the bow. This is attached to a triple chain of #64 rubber bands that reach up to an eyehook in the ceiling. A triple chain means you make a rubber band chain with three rubber bands at a time. This chain will connect to an eyehook in the ceiling and needs to be long enough that the bow will gently rest on the table in an upright position. I like the rubber bands because they are inexpensive and simple. This suspension method lets the bow float as though it had little weight and is much simpler than the weight and pulley systems I have seen. This suspension system uses very little space and is what I used back in my apartment days. It works so well I keep using it.
9. THE CUTTING BOW POWER SUPPLY WIRE. Make sure you connect to the 24 volt connections on the transformer. Cut off both ends of a regular two-wire 13-amp 1600-watt extension cord wire. Attach 12-15 feet of the wire to the bow. Alligator clips with insulating covers are recommended for attachment to the cutting wire.
10. THE SECOND ON/OFF SWITCH. I put a house light on/off switch on the end of the bow without the rubber bands. (See the schematic.) Put a regular switch plate on the front of the outlet. Make sure you silicone the back of the switch so you cannot ever touch the bare wires. This switch lets you control the power without letting go of the bow.
11. THE CUTTING WIRE. I like single strand 0.020 chrome nickel alloy fishing line. The 0.018 is rated at 69 pound test. The 0.020 is rated at 88 pound test. This wire keeps the amps to 3-4.5 on the transformer. Check the amps before you cut whichever wire you choose. You don't want transformer failure. The cutting wire is wrapped around the chain link a couple of times and then around itself several times. Try not to kink it because it will be weak. A broken wire can cost you a foam core or a knuckle or two especially while stretching the rubber bands. A source for this wire is listed at the end of the instructions.
12. ELECTRICALLY ISOLATE THE CUTTING WIRE. You need to try to electrically isolate the wire so that you can only make electrical contact with power by touching the cutting wire itself. Insulate each of the spikes with heat shrink or electrical tape and wrap a strong small cord through the chain link several times; tie and superglue it so it isolates the cutting wire from the spike by leaving a small gap. Make sure this connection is strong because there will be tension on the wire.
13. RUBBER BANDS AND CHAIN LINKS. There will be one 1.5" chain link on the switch side of the bow and two of the 1.5" chain links that are still connected on the rubber band side of the bow. I leave a 6" gap to put the #64 rubber bands across to properly tension the cutting wire. I usually have 4 or 5 #64 rubber bands doubled through the chain link and stretched around the spike. The rubber bands automatically adjust the tension as the wire stretches and have enough stretch to tolerate the anchor for the bow that will be described later.
14. THE OUTLET RECEPTICAL BOX. I have installed my GFI outlet, my dimmer on/off switch and the wall outlet in a regular three fixture plastic receptacle box. I use a matching face plate to cover all electrical wires. I wish I could also get the transformer to fit but I haven't figured that one out yet. I mount the box on a piece of wood and mount the transformer next to it making sure the transformer frame is grounded to the GFI. I also put silicone or hot glue on all exposed transformer connections to prevent accidental contact. No bare wires should be exposed anywhere on the power supply.
I hope this information will be helpful. I am a hobbyist not an electrician or an engineer. What I am going to tell you is the way I have made my foam cutter work for me. There are many other good ideas out there and I encourage you to seek out other ideas and methods to make your foam cuts as safe and precise as you can.
