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Hot Wire Cutters - Project 1

by Gary James

The deluxe version of my toolGiven that a hot wire cutter is one of the more expensive additions to a terrain makers tool kit, and that they are sometimes hard to obtain, it's hardly surprising that many people consider making their own. If you are thinking of doing this we strongly suggest that you check out our general information about hot wire cutters and our reviews. Given the difficulty and cost of obtaining parts, and the work involved in making you're own, you might conclude that a hot wire cutter is one item that your better to save up for after all. For the benefit of those who remain undeterred, Gary James tells us how he made his own hand held hot wire cutter:

Please do not attempt this, or any other project involving electricity unless you are competent and confident to do so. Get some help if necessary. You should also read this document to acquaint yourself with the potential hazard from toxic fumes that can be generated when using a hot wire cutter.

After a lot of experimentation I found a way of building a hot wire cutter that I am happy with. The construction of a cutter is straightforward... the difficult part is finding the correct combination of wire and power supply. This project describes the power supply and wire used in my own cutter. It works well, and provided you use exactly the same combination I see no reason why yours shouldn't work too. However I take no responsibility whatsoever for the outcome of your own project.

An important point to understand is that a longer wire will get hotter than a short one under the same current. This is because the special nichrome wire being used gets hot because it resists the flow of electricity. The longer the wire, the greater the resistance, and therefore the greater the heat.

To make the wire hotterTo make the wire cooler
+ Use a thinner wire- Use a thicker wire
+ Use a longer wire- Use a shorter wire
+ Increase the power- Decrease the power

Materials

I have included instructions for two cutters - a basic model and a deluxe version. Here are the parts needed for both models:

A piece of sheet material to make the U-shaped frame. This must be a material that does not conduct electricity, and is strong enough to hold the wire taut. I used 6mm MDF. You could use plywood or hardboard too. To make a cutter the same size as mine you will need a piece 288mm x 230mm.

Hot Wire Cutters - Project 1A power supply with an output of 9 Volts and 1 Amp (sometimes labelled as 1000 mA rather than 1 Amp). You might get away with 12v instead of 9v, and/or up to 1.3 Amps (1300 mA) but don't blame me if the wire melts! I bought the type that plugs into your house supply that often comes with small electrical gadgets such as mobile phones. This has a two-strand low voltage output with a small plug on the end.

The prices for these vary tremendously and I got one very cheaply on Ebay. Be sure to get one that is correct for your country.

Hot Wire Cutters - Project 1A supply of wire of exactly the right type and gauge (thickness). You need bare Nickel Chrome wire with a gauge of 0.25mm (33 SWG). If you cannot find a local supplier the UK one I use will ship worldwide: The Scientific Wire Company.

For the basic model you will also need:

Hot Wire Cutters - Project 1Two small bolts with four nuts, and ideally a couple of wing nuts if you can get them. The ones I used were 4mm in diameter and 30mm long. Most hardware stores sell small packets of bolts and nuts like this. Buy ones with flat heads.

You can do without the wing nuts if you can't find them in which case you will have to use a small spanner to fix your wire in place.

Making the basic cutter

Step 1 : Take your sheet material and draw out the U frame:

Hot Wire Cutters - Project 1This diagram shows the size and shape of my cutter. You can make one of any size you like, but remember that if you make the opening a lot bigger than the 110mm (4 1/2 inches) that I used your wire may get too hot. You can access a larger image here if you want to print it out.

The diagram below is a simple construction drawing to help you lay out the shape if you want a cutter exactly the same shape as mine. Again, you can access a larger image here if you want to print it out.

  1. Draw a rectangle 288mm by 230mm

  2. Draw three lines 40mm in from the edge along three of the sides (A,B,C)

  3. Draw two lines each 20mm in from one of the first set along the long sides (D,E)

  4. Draw on the dotted lines to get the basic cutter shape (F,G,H,I).

  5. Draw around a small round object to get the curved corners.

Hot Wire Cutters - Project 1

Step 2: Cut out the frame

Hot Wire Cutters - Project 1Using a hand saw or a jig saw cut around the frame. You might want to rub out or scribble over the construction lines first so you don't follow the wrong line. Smooth off the frame with sand paper so it is pleasant to handle.

Drill out two holes in the ends of the arms to take your bolts.

Step 3: Connect the wires to the bolts

Hot Wire Cutters - Project 1Cut the small plug off your power supply (NOTE: do not do this if you might want to make the deluxe version). Pull the two wires apart so that one strand of your two-strand low voltage wire can go to each bolt. Strip off 25mm of insulation and twist the copper wire around the bolt.

Step 4: Fit the bolts to the frame

Hot Wire Cutters - Project 1Slot your bolts through the holes in the arms of the cutter. Screw a nut down very tightly, clamping the low voltage power supply lead between the nut and the frame. Add a second nut as a lock nut and tighten it up against the first.

Step 5: Fit the cutting wire

Hot Wire Cutters - Project 1Cut a length of Nickel Chrome wire a little longer than your frame opening. Fasten one end to a bolt by winding it around the bolt and tightening up a wing nut.

Squeeze the arms of the frame together slightly and wind the other end of the wire around the other bolt, clamping it securely. Squeezing the arms of the cutter together while you do this helps to get the wire nice and tight.

Step 6: Tidy up and test the cutter

Hot Wire Cutters - Project 1Use some tape to fix the wires along the arms of the frame. This picture shows the underneath of the cutter with the wires going to the bolts.

Plug in your cutter and test it on some foam!

Making the deluxe version

If you can get the parts and are able to do some basic soldering you can make a cutter with some useful extra features. You can get these items from electrical component suppliers on the net, such as Maplin in the UK (www.maplin.co.uk). For the deluxe version you will need:

Hot Wire Cutters - Project 1A couple of terminal posts (also called binding posts). These are specially designed for connecting wires, and replace the bolts and wingnuts to secure the cutting wire. The advantage is that they are easier to fasten and release, and look neater.

Some insulated wire to connect the power socket, switch and terminal posts.

Hot Wire Cutters - Project 1A small push button switch (on the right) to turn the power to the cutter on and off. Buy a 'push to make' switch (ie, the circuit is made when the button is pressed). Make sure the threaded collar of the switch is long enough to come through your frame. Ensure that the switch is rated to take the power you are using (9v and 1 Amp in my case).

A small socket to take the low voltage plug on your power supply. This is neater than cutting the plug off and allows you to use your power supply on a second tool, such as a bench hot wire cutter.

Step 1: Cut out the frame just as for the basic version

Step 2: Drill the frame to take your terminal posts, switch and the socket. Place the power socket in the bottom corner of the frame, and the switch in a place where your thumb naturally falls when holding the cutter.

Step 3: Assemble the posts, switch and socket into the frame. Be sure the connections are all on the same side of the frame.

Hot Wire Cutters - Project 1Step 4: Solder a length of insulated wire from one terminal of the power socket to one of the terminal posts (blue in the diagram). Solder a length of insulated wire from the second terminal of the power socket to one terminal of your switch (red in diagram). Solder a final length of wire from the second terminal of your switch to the other terminal post (red in diagram).

(The components in the diagram are not to scale.)

The image below shows my finished 'deluxe' wire cutter. The power supply plugs into the socket in the bottom corner of the frame, and the white push-button is easily operated by my thumb. I have tidied it up underneath by covering the wire and the terminals of the switch and socket with insulating tape.

Hot Wire Cutters - Project 1

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