Scrappy Hot Wire Cutter

This is my first instructable so it's also kind of scrappy, messy, not really refined. It just had to be made.

After seeing a few Instructables on hot wire cutters and wanting to spend nearly nothing on one, I gathered the following parts and made one.

Parts:

1. (1) 10x32 x3" machine bolt
2. (3) 10x32 x2" machine bolt
3. (1) 10x32 x1" machine bolt
4. (7) 10x32 nut
5. (1) heavy solid core wire 12", like 20 amp Romex.
6. (1) wood scrap for table, 10" x 5"
7. (1) scrap of wood for feet
8. (1) spool of nichrome wire
9. (1) auto fuse, 6 amp.
10. (2) female spade connectors
11. (1) power supply 12v 2 Amp
12. (1) 1" PVC pipe cap
13. (1) 1" PVC ell
14. (1) 1" PVC pipe, 12 inches.
15. (1) 18 gauge wire for power
16. (1) wire nut or solder.
17. zip ties, electrical tape, connectors of your choosing.

Tools:

1. Hand Saw
2. Drill
3. Crimper
4. Wire cutter
5. Wire stripper
6. Needle nose pliers

Optional but recommended:

1. Soldering iron and solder.
2. Heat shrink tubing.
3. High amp DC connectors.

Creating the table is easy. Here I'm just holding the parts to get an idea of the final shape.

Drill a hole in the wood and the cap where you want the mast to be, centered near the back. Use a 10x20 nut and bolt to secure the PVC cap to the table.

The PVC mast needs some holes drilled for holding the nichrome wire and stiff wire extension. Two at the stubby end, one at the long end, and one at the elbow. I found that it was easier to drill the PVC elbow from each side instead of straight through to make a better alignment.

Assemble the mast and table but don't glue anything, it's easier to adjust and put away if you can disassemble it.

To create the stiff wire extension, bend the heavy solid core wire as shown into a hook and loop.

The hook end goes in one hole, the loop is firmly attached with a 2 inch 10x30 machine bolt.

Check that the heavy wire extension is long enough before trimming. Leave enough wire to form a hook above where the nichrome will go through the table. The heavy wire extension also protects the PVC from the heat, it is important to not have the nichrome wire touch anything that melts.

Use some string to test routing of the nichrome wire path and find the point on the table where the wire will be vertical. It's a good idea to try and center stuff as much as possible. When you have found where the wire should go through the table, drill a hole there. Note how the nichrome is held away from the PVC mast.

For the bottom I decided against wood screws, being too long and such. So instead I used a 1" machine bolt and countersunk it. Again I made a hook in the heavy wire but left enough wire after the hook to act as a handle for adjustment later.

You should really use a fuse when dealing with high current DC devices, and they are easy to inline, just get two spade connectors, a fuse, and a crimper. If there is stress from the wires, zip tie them together.

The wiring is very easy. From power positive to fuse to nichrome wire back to power negative. The alligator clamp is to change resistance if needed. Here the feet have been glued on, one of the feet has a hole drilled to manage the return wire. I've soldered the return wire (ground, to power negative) to the heavy gauge wire but a wire nut could be used I suppose.

The pipe behind the nichrome is just so you can see the wire.

When winding the nichrome wire, keep the following in mind:

1. The wire should be vertical.
2. The wire should be under tension.

This is actually pretty easy, just tie the nichome to the bottom, pull the top tight and tighten the nut securing the wire, and then adjust the heavy Romex wires. Note the heavy Romex wire is bent down from tension. It isn't very much since the heavy Romex extension acts as the spring, so it's only a little tension, enough to make the wire straight.

Before attaching a power source, you should measure the resistance with a multimeter. I measured 11 ohms without using the alligator clip, and 6 ohms when attached at the top hook. This meant that 1 to 2 amps would be going through a 12 volt dc source. This seemed reasonable. Power is volts times amps, so again with a little fudging, 12 watts to 24 watts.

The first test cut worked. Amazing. Also the released gasses are very nasty so do this outside! A test of closed cell foam also worked. I decided to try a small project.

I decided to make an Instructables Robot out of closed cell foam and a printout.

Stencil
I printed out the Instructables Robot and went over it a few times with a marker to try and transfer it to the closed cell foam. I then drew directly on the foam to create a path to cut. I then cut it out, printed a color version of the robot, cut that out, and glued them together. Not bad for a first try.

When cutting very narrow pieces, you could see the individual cell strands.

Assembly

This final shot shows the alligator clamp at an intermediate position on the nichrome wire, as I needed a little more power.

So there you have it, it's time to make a hot wire foam cutter.