Hotwire Foam Cutting Table Electrical

Constructing the Table

This is the second part of my guide on building a hotwire foam cutting table.  In the first part of this guide we constructed the table.  Here we are going to wire up the electrical parts of it so the NiChrome wire will get hot enough to cut the foam.

Covered in this article:
Wiring
Using your table

The components for the electrical side are fairly simple.  You need some NiChrome wire (I got 30 feet of 33GA wire off eBay for $5.99 including shipping), some electrical wire, and a power supply.  I got my power supply from Radio Shack and it's a 3-12V adjustable power supply.  I think it was meant as a replacement power supply for a number of electronic goodies but it works good for this application as well once you cut the connector off.  You will also need some wire nut connectors similar to these from Home Depot.  I found a small pack that was only a couple of dollars that is much better than the large container since we only need a couple of them for this project.

First lets connect our wires up to the eye bolt that is holding our NiChrome wire.  Expose a section of the wire at the end then pinch it between the two nuts on the eye bolt.  Put these nuts as far towards the eye part as possible so you have the most room possible for tensioning the cutting wire.
	Next run the wire down the cutting arm.  I used a staple gun (similar to this one from Home Depot) to hold the wire in place.  I used black wire for the cutting arm and red wire underneath the table.  However, you can use whatever color scheme you want, even use one color for the entire thing.  It really doesn't matter on something as simple as this, I just did it so I could easily tell which wire went where.
Here's a close-up of the wire being held by a staple.  You need to make sure that the wire is in the center of the gun or you might penetrate the wire with the staple and cause a short or shock you if you touch it while the power is on, and that's generally what is considered a bad thing.
	Here is the wire attached to the lower cutting wire bracket.  I chose to solder the wire to the bracket to hold it in place.  You can easily just use a small bolt and pinch the wire like we did on the eye bolt.  If I had to do it over I probably would use the bolt method because (in case you can't tell) I suck at soldering and it took me forever to get something to work that I was happy with.
Here you can see where the wire runs under the table.  I simply used the staple gun to attach it to one of the legs and ran it to the back of the table.  Nothing fancy here.
	Here's a shot of our power supply.  Originally I think it was supposed to be a replacement power supply for a number of different gadgets and you can get different plugs for it to attach to.  I got this off the Radio Shack web site here.  There are other links to it scattered around this article but if you're like me you don't want to have to go digging for them so here it is again.
It almost seems a shame to cut up a neat little thing like this.  But I did it anyway.  All you have to do is cut off the end plug then separate the two wires where they were connected to the plug.  Then expose a bit of the wire inside so we can use the wire nuts to attach them to our table wiring.
	Here you can see the connection to our table wiring from the power supply wires.  There's nothing complicated about it just gently wrap the metal ends of both wires around each other (twist them together) then screw on the wire nut and the connection is complete.  It really doesn't matter which one goes where since the wire will get hot no matter which way the current is flowing.  I could have put a switch here to turn the table off and on but I chose to make it as simple as possible and the way you turn the table off and on is to plug it in or unplug it.  If you were going to put a switch (not covered in this article) then you would put it here between one of the wires to the power supply and the table.
The final step for our table is to attach the NiChrome cutting wire.  I attach it to the bottom bracket first because there's not as much room under the table as at the eye bolt and you don't have to worry about tension or anything else while putting the cutting wire on.
	Next attach the cutting wire to the eye bolt on the cutting arm running through the hole in the table.  Try to get the wire as close to the right tension as you can here so it's less work to get it later.  To adjust the tension on the cutting wire simply tighten the wing nut then once you get the tension you want run the bottom nut up to the bracket and make sure the wing nut is tight.  You have to have the bottom nut up to the bracket or the eye bolt will move when you try to cut something.  If you want to loosen the wire, either for replacement or to swing the arm up, simply loosen the wing nut do whatever you want and replace the wing nut and tighten to the proper tension. Tensioning sounds complicated but it's really not.  After you do it once it's very simple to do.

Using the table

To set up the table to cut a piece of foam first you need to set the guide board.  To set the guide board take your ruler and measure out the distance you want to cut from the cutting wire.  Place the guide board at this distance and use the spring clamps to hold it in place.  You need to pick the voltage on the power supply before you plug it in.  If you pick something too high the cutting wire will glow briefly then melt and you have to replace it.  While this is kind of neat to watch it's not desirable.  I went with the 3 volt setting and it works fine.  The 4.5 volt setting causes the wire to glow which is way too hot and will shorten the life of the wire (it looks cool though).

Here is the table set up to cut a 2 foot piece of foam for a Flames of War modular table.

You make the cut on one side then rotate the piece 90 degrees and do a second cut and bingo!  You've got a 2 foot square table piece ready for you to turn into a modular table section.  I actually set the table to cut 1/16th of an inch short of 2 foot.  This is because the friendly local gaming store has a frame built around the edge of their tables to keep models, dice, and other stuff from falling over the edge.  The extra 1/16th of an inch gives me enough space on one side of the table to reach down and remove a piece without much problems.

Here's a shot of the tape measuring the piece after cutting

And finally a stack of cut pieces ready to be turned into an Omaha beach table.  They're leaning back against my exercise bike so they don't end up perfectly flush.  I couldn't figure out how to get them to all stand up perfectly straight AND take the picture at the same time.  More on the gaming table in a future article.

Conclusion
I had fun with this project and I've already used this table for several other things I hadn't anticipated.  This should be a useful piece of equipment to keep around for a long time.  If I had to do it over I probably would have made the height of the cutting arm 4 inches instead of just 3 so I have more room to work with.  That's just me, the 3" height works perfectly.  At some point in the near future I'm going to be making an attachment for the cutting arm to allow circular cuts of the foam but that will be a later article.