Styrofoam Cutter

As you know by now one project leads into another and that leads into............well you get the point. Well I need to back up about three projects to get to this point. For X-mas 2007 I had received a power speed boat called the Nitro Hammer from Tower Hobbies . I tried breaking it in in the garage but succeeded to break the engine. That's a whole other story. Anyway, I got the part to fix the motor the first week in August of 2009. I took the boat up to our cottage on the river and went out and proceeded to hit the dock on the first outing. Only minor damage to the nose. I didn't have it at full throttle or I would not be writing about this project. Anyway to make a long story short I get several runs in the next day. One problem with a nitro powered boat. If it quits out in the water you need to go get it. I used a friends jet ski to do this. A bit of a pain, but it worked. So during one of those rainy days I came up with the idea of a rescue boat. One powered by electric motors to rescue my stalled boat. So I figured styrofoam would be the ideal thing to use. I started carving some blue styrofoam up. Not a pretty sight. Then I remembered all the styrofoam cutters that I'd seen made for building real hover crafts. Ah! that's what I needed.

This isn't a tutorial on how to build foam cutters but a general description of one I built. Sizes can vary for what ever size foam you need to cut or what ever size of your project. I'll give general dimensions. You can use those to size your own cutter.

	First you need a board to slide the foam over to cut it. I used what was left from a tread mill. It's the piece that supports the belt that you walk on. It is MDF and coated with what I assume to be some kind of plastic. I made mine 1foot by 2 feet. Large enough for the rescue boat project. I drilled a 1/2" dia. hole at mid point of the board. Just above the board is what's going to be the overhead arm to hold the nichrome wire. It's what was left over from a project using MFD. I'd cut it apart there.
	I turned the front cut off portion around and will attach it to the other part using glue and screws.
	But first I added a frame around the outside made from scrap wood I had laying around. I cut a rabbit in it just deep enough to let the board stick above the sides by about 1/16".
	Added some glue and used a brad nailer to hold it all together.
	Next came the assembly of the over head arm.
	This is what happened to the MDF. Even with a hole drilled for the screw, the MDF still split. I used a piece of pine instead. I made the grove in the other piece of wood wide enough to fit the 3/4" pine in and glued and screwed it down.
	I also cut a dado in the frame to accommodate the whole over head arm assembly and screwed it into the frame.
	While I waited for the glue to dry I came up with a power supply. It's a computer power supply that I used the 12 volt supply from. I needed to figure out just how much wire I needed to get it just hot enough to melt the foam for the size nichrome wire I'm using. So for wire .015" thick, I needed about 19 to 20 inches of wire. This turns out to be about 6 to 7 ohms.
	Here's a sample cut. Looks good. Now back to the cutter.
	You'll notice I've only got about 6.5 inches. Not quite enough.
	My next plan of attack was to use some aluminum to make the over head arm. Problem was when I cut the flat piece in to two smaller strips I was going to put them on the mill and mill the edges parallel. Unfortunately I only had a couple to t-nuts to hold everything down and it didn't include the two strips. This has lead to another project of making T-nuts for the mill. But that another subject.
	I dug around in my spare wood pile and came up with some more 3/4" by 3" wide pine and a 2" X 4" I could use. A few pieces of wood and some glue and screws and I had assembled another over head arm.
	Here's a better view of the dado that the 2" X 4" fits in.
	Fitted and screwed in. No glue. I might want to change this at a future date.
	And there we have it. Now I need to add the arm and other parts.
	Here I'm setting up two pieces of aluminum angle's. I'm using 1" angles for this. I drilled two holes using a #2 drill to clear the 1/4"-20 screws and wing nuts that will hold the angles on the wood.
	Next two of the same holes, #2 drill for 1/4"-20 screws. I screwed a piece of aluminum block with a hole through the top between the angles. This will support the upper end of the wire.
	What you see here is a 1/4"-20 bolt with the head cut off. I then annealed the bolt and drill a hole through the bolt. Then I cut a slot with the Dremel cut off disk so I could hook the wire into it and tighten it up with a nut on the top. Also note how I wrapped the wire around itself.
	I cut off a piece of copper pipe and threaded it over the twisted wire.
	Then the piece of pipe was squeezed to hold the wire from coming unraveled. I did the same for the other end except I used a piece of brass bar to hold the wire.
	Here I'm doing a trial cut with the computer power supply. I later used a 15 volt power supply that I found.
	Here's the same piece. The cut looks very clean.
	A final view of the temporary hook up using the 15 volt supply. I use an alligator clip to adjust how much heat the wire puts out by moving it up and down the wire. The further down the hotter the wire gets. Careful you don't get it red hot or it can catch the foam on fire. Use extreme caution when cutting foam like this.

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