I do not normally do much with Styrofoam as it always feels like I end up with a large mess of little white chunks that stick to everything and hang around for months after the event. But here I find myself carving some items out of foam to later be hard coated and molded. But this time I have decided to build some temporary tooling to ruff cut the foam into basic shapes to reduce the amount of carving and maybe mess. So using some scrap material around the shop we will build a large 55 inch cutter for a single use and an smaller cutter with a table base for more usage but still very limited to likely less than half a dozen times. But this table version I think I will keep around on a shelf (folded up) for potential usage in the future.
Large Bow Cutter
For the one and done 52 inch cutter I have ripped down some scrap t1-11 siding to 3 inches wide. This piece has additionally been trimmed to 50 inches long creating the spine of the cutter. The arms are made out of some scrap trims of ¾ inch plywood and screwed to the spine with three drywall screws at a slight angle. Additional drywall screws have been placed at the ends of arms for mounting the nichrome cutting wire and a small spring to keep the wire tight as it heats for cutting. To get power to the cutting wire I am suing some scrap 16ga copper I had in the drawer, the nichrome is 26ga and the only thing I bought for the cutter. Using an online calculator (why do the math by hand) http://www.jacobs-online.biz/nichrome/NichromeCalc.html we can back into the needed voltage and current based on the wire size and length and needed 600F to 700F degrees. For this I got about 26 volts and 2 amps, as this is a scrap project I am using the closest thing I have which is a 24 volt 20 amp supply which makes the wire a bit on the cool side but works so I have added a small piece of copper wire to one side to effectively shorted the cutting wire three inches brining my temp up for the 24 volt supply. This works for me as the billet of foam I am cutting into a cylinder is only 48 inches wide.
|single use bow cutter next to foam block
|lower arm showing nichrome wire attached to spring, power lead and arm.
|The table version foam cutter I am starting with a scrap piece of melamine and squaring it up in the table saw to be an 18 inch square. This size is completely arbitrary and based on the largest square I could extract from the scrap. I them ripped down some scrap 2×4 into 1.5 by 1.5 inch sticks about 40 inches long. Again this length is solely based on the length of the scrap, but we will need enough to build a base on the melamine so four 18 inch pieces if you miter cut or something a little different if you just but the pieces together like I have done.
|View of the table bottom showing how the sides are attached. Plaase note that all the wood is glued and screwed together for strengh. The black wire coming through the side is the end of a wall power supply. The supply converts wall power down to 12 volts dc at a max of 5 amps. Much less current is needed but this is what i had in the parts drawer. You should calculate the needed voltage and current based on your cutting wire length. http://www.jacobs-online.biz/nichrome/NichromeCalc.html
|trim from the 1.5 by 1.5 I ripped down for the sides holds a screw that provides a mount for the nichrome wire and power cable. The Nichrome wire passes through a 1/4 inch hole in the the table top
I did not feel like clearing some stuff from in front of the metal saw so I have built the arm that holds the upper end of the cutting wire out of some scrap 1 inch PVC I had. The size of the pipe was a bit odd and I did not have a drill bit that size so I measured the outside of a 1 inch coupling and found it to need a 1 5/8 ths hole and I have a bit for that. So my version has a coupling glued into the table platform with the arm inserted into the fitting for a good fit.
This worked fine for holding the pipe straight but the tension I have placed on the nichrome wire is causing the arm to bow a bit and the wire to tip forward about ¼ inch over the 25 inch height making it not square to the table. If you are only cutting thin material this likely will not be an issue but if I was needing more precise cuts it would have been an issue for my 20 inch deep cuts. If I use this again in the future I will replace the arm with some ¾ inch steel tube bolt it to the side of the table.
Some scrap solid rod I had made a perfect holder for a 10-32 screw to hold the wire and spring. On the inside a piece of 14 ga copper is attached to the head of the screw and runs through the pipe into the base
|First cut in making a candy shape on the cutter