[benjhind]

Hello everyone, I'd like to share how to make a VERY simple foam cutter, as I think it would be useful to a fair few people. The cost to me was about $45 for the transformer, and $6 for the dimmer. Everything else I had on hand.

Notes:

- Credit for all info in this post goes to Brad (RCC user igor_throw_the_switch) who provided me with all of the information I needed to put this together. Thanks Brad!!

- I know nothing about electronics or electricity. Please point out where I've made mistakes or could reword things to make this more accurate.

Parts List:

Project box
- For putting the components in.

Dimmer switch
- 600W single-pole with built in on/off switch.

Transformer
- I have heard that 24V is a good place to start. 3-5 Amps is required. I went with a 24V, 4A transformer for this project.
- If you have no idea where to get a transformer (like me), you can order them from www.allelectronics.com
- On the website, scroll down and choose "Transformers" from the menu on the left. Go through the pages, and pick out TX-243 (24V, 3A), TX-244 (24V, 4A), or TX-245 (24V, 5A).
- Be prepared for high shipping costs. My 4A transformer was almost 4 lbs, and I paid $16.16 USD for shipping (I bought a few other items as well to ease the pain).

Power Cord
- Needs to be 3-prong. I recycled an old PC power cord.

Wire for bow
- I used an acoustic guitar string, note 'b', .016" diameter (non-wrapped!). I have lots of old strings on hand, so thats what I used. Lots of people use fishing leader line as well.

Wood for bow
- All the wood I used for this project was salvaged from an old clothes drying rack that broke.

Cord for bow
- I used an old cord from a two-prong plug. This came off of an aquarium light that I threw out.

Deans Connectors (optional)
- I opted to have my bow detachable.

Instructions:

Here is a wiring diagram for the cutter which was stolen from Brad (igor_throw_the_switch):



Note: My project box is of poor design and does little to prevent the user from electrical shock! Please close your project in better, with a few vents for cooling the transformer.

1) I started by mounting my transformer to the bottom of my home-made project box. Please note that after taking this picture, I turned the transformer around to have the 24V side face the outside of the project box.



2) Next I soldered on the leads for the bow to the 24V side of the transformer, and routed my plug leads through the top of my project box. I ran about 2' of cord, and put a female Deans connector on this to hook my bow up to.

Please note that my transformer had three poles on the 24V side. They were labelled 12V-0V-12V. Hooking a wire up to one of the 12V poles and the 0V pole will result in having a 12V bow. Using the two 12V poles results in a 24V bow (this is what you want to do, you didn't pay for a 24V transformer just to use 12V!).

[benjhind]

3) Next, I wired in my dimmer switch. I wired the green (ground) wire to the ground on the dimmer. The black wire from the plug is wired to one of the black wires on the dimmer, and the other black wire from the dimmer is wired to one of the 120V poles on the transformer. The white wire from the plug goes directly to one of the 120V poles on the transformer. As far as I know, it doesn't matter which way these wires are hooked up.



4) I then sealed my box up. This is the completed power supply for the bow.



5) I made up a quick-and-dirty bow for my foam cutter. I had these wooden pieces handy, which came from an old laundry rack.

If you want to replicate my bow exactly, the pieces are about 20" long, 3/4" wide and 1/4" thick. There are holes at each end and in the middle. I used a pair of these pieces for the middle section, and attached each end to the middle of a single piece of the same size using a dowel. The tension holds the whole thing together, but you could glue your dowels in place.

Between the bottom holes I strung my guitar string. I used the eyelet from the guitar string to loop the string through at one end, and just tied the other end in some crude knots.

At the other end, I used some butcher's cord for tension. I did this by tieing a loop in one end and running the string through the holes and back through the loop. Pulling back on this, you can get some good tension on there. If you've got a good strong spring, that would also be a good option.

I soldered an end of my bow cord to each end of the guitar string. I routed this up the arms fo the bow, and attached it to a male Deans connector. Hooking this up to the power supply gives us a working foam cutter!!



Tips:

- Use Deans or some other sort of connector (ie. banana jacks) to make your bow detachable. You can now make a dozen bows of different lengths, wire diameter, etc. It is also easier to store this way.

- Before hooking up your bow, use your voltmeter (set to AC) to figure out which way is "up" and "down" on your dimmer, and whether it is on or off. Mark your dimmer to show you how to turn it up or down. Start off at a low setting, and heat your wire up enough to cut your foam. If you heat it too much, you might snap your wire.

- A light would be a good way to see whether the cutter is on or off. I didn't include one, but likely should have. You could also use a separate on/off switch. With the push-button switch on the dimmer, I can't tell whether it is on or off (other than the hum from the bow).

Conclusions:

I'm not very good at working with wood! I'd better stick to SPADs and foam planes...

If I can build this, anybody can! Please give some feedback as to how this post can be improved and I'll add in the changes.

Hope this helps a few out there. It has been two years since I posted my "DIY Power Supply" thread and I still get PM's saying that people have gotten some helpful info out of it, and I hope to see some people using this as well.

Again, a huge thanks to Brad (igor_throw_the_switch) for all of the above information.

Ben

[Daren71]

That looks good Ben. What will you use as a template for the wing shape? I've seen foam cutters, and foam wings, but you have to have an original right? Daren

[g-manz35]

I'm making a list and going shopping.

Thanks Ben.

George

[benjhind]

Hi Daren,

You can make a variety of wing shapes with one of these. I plan to do this by using home-made templates.

Basically, you use two pieces of wood. One is the shape and size of the root of the wing, one is the shape and size of the wing tip. You cut a foam block to the length of the wing, pin your pieces of wood to either end, and run the bow across the two pieces. This gives you your basic wing shape.

I hope some of that made sense. I actually don't know much about working with foam. I just want to build a variety of small electric "park flyer" sized aircraft and try out a variety of designs.

The original thing that got me working on this was that I wanted to make a park flyer that was a light-weight, easy-to-build, 4-channel trainer. I think the hobby market is lacking in these. People love the GWS slow-stick, but you've got to modify it to have ailerons.

George: Good luck! I'm sure that you can get transformers in a variety of places, but I didn't know where to look.

Cheers!

Ben

[Don H]

Well done Ben, I upgraded all my cutting gear to 4 axis CNC (which I haven't re-assembled living in the apt.) but this works. I hope ya have lots of cutting success with your setup.

Don

[Don H]

Let me rephrase that..sorry. Mine is just x-y axes that all move independantly.

Sorry, Don

[Spitball]

Benji, did you use a regular light dimmer or a heavier fan speed or the like dimmer? I wouldn't have thought a light dimmer would be usable for an inductive load like a transformer. What you think Igor-tts? One other point, you need more voltage, not amperage for a longer or thinner wire. Good work and many will want to copy yours.

[benjhind]

I think my dimmer is just a regular 600W single pole light dimmer.

When I throw the voltmeter on it, it doesn't exaclty ramp things up smoothly, so you might want to invest in something a little better.

I'll make that change about the voltage / amperage. Like I said, I don't know too much about this stuff

Ben

[moo]

Cover all mains connections with electrical tape please, including marrettes.

Some suggestions for mkII:

Push the cables in more and put a figure eight knot (less strain) in the jacket (not the unjacketed wires).

Fireproof or fire resistant box.

Suggestions Igor?