Hot Wire Foam Cutter

First things first

Warning, electricity and heat can be dangerous if you're not handling it correctly. Know what you're doing or don't do it. Don't touch active cables! Even tho this is a low power application you should always exercise caution! This is a hobby device and not a professional or industrial grade device!

Usually nichrome wire is not food safe. So it's not a butter knife.

This device will melt/burn the foam. This will release fumes similar to what you know from ASA or ABS. Even materials that are considered to be safe like PLA might release toxic fumes if heated up above the approved temperature! So use it in a well ventilated area or even better outside. Don't inhale the fumes!

General

I don't know if the urge to have an electric foam cutter or the project that created the need for an electric foam cutter has been first.

This model will require a print bed with about 220x205. If requested I can also offer it in different sizes, but it fits my print bed and my needs well, hence I did go with this size. 

It's really addictive and funny, don't forget you had a project you were working on. Or if you need a reason to justify getting the Foam Cutter, have a look at the XRP Amphibious. :D

The design has been inspired by H steel bars modified to be 3d printer friendly. 

Print Settings

No support or brim is required. No special settings are needed. The model has been designed in a very printer friendly manner. Because we're dealing a bit with heat and tension I did go for PETG rather than PLA. ASA or ABS will also be a good choice. I wanted it to be quite durable, so I did go with 4 walls and 50% infill.

You can make an optional PAUSE at layer 63 in case you want to place the wires while printing rather than fiddling around afterwards.

Additionally needed

• 2x M8 bolts, total length of 20mm or longer
• 4x M8 nuts
• Nichrome wire, e.g. 0.2mm width
• Wire, 26 AWG or thicker.
• A power supply (depends on your setup)

Power Supply

What power supply would be the best pick for you can be calculated, I found this Nichrome Wire Calculator online and used it for a rough estimation. It also offers you a lot of information if you want to dive deeper into this topic. My input data has been

• Nichrome 60, 32 Gauge, 10 inches
• Copper Lead, 26 Gauge, 6 feet
• 800 Fahrenheit

Eventually it told me to use a PSU with 10.2V and 1.13 Amps. I'll use a lab psu, but if you don't have one you can alter the temperature to see what might fit your need. E.g. if I increase it to 960F it told me I can use a 1.3A with 12V which is more mainstream.

Assembly

As mentioned in the Print Settings, either you did add the wires to the frame during printing or you do this now. Keep them longer for now. You can cut them to size later.

Put the bolt in from the bottom of the frame and lock it in place with a nut on the other side.

Remove about 4cm of the copper wires isolation and wrap it along with the nichrome wire around the bottom of the thread, secure it in place with another nut. Proceed the same on the other end and ensure the nichrome wire is firmly stretched and both cables are well connected to the screw.

For the other side it depends on your power supply. I did just solder some DuPont connectors to the end and finish it with some shrinking tube. I can easily connect that to my PSU.

This does not have to be perfect. If e.g. one cm of the nichrome wire would stand away, it's nothing to worry about. Same with the screw. Electricity will always go the way of the least resistance. So there's no reason for the electricity to flow to the “open end” or thru the nuts. Just take care that the copper wire and the nichrome wire touch each other.

Usage

Ensure your device is in a good condition and isn't worn out, there are no loose cables, cable isolation is not damaged, everything is well attached and locked in place. 

If you're using a lab bench, set up the specs first.

Ensure your hotwire is not touching anything when you connect the foam cutter to your psu and power it on.

Wait till it heats up and that's it, have fun.

When you're done, turn off your PSU and disconnect the foam cutter from power. Clean the wire with some paper towels.

Troubleshooting

It's not getting hot?

Turn off your PSU and disconnect your device. Take an ohmmeter and measure the resistance of the hot wire. If it shows you infinite it might have some isolation in form of a coating. It's not really common tho. Maybe you need to check your PSU. e.g. modern PSU that will provide you multiple voltages do require a negotiation. If you skip this step you will only get the minimum out of your PSU. You should look for another PSU then. An alternative would be a decoy board.