In these pictures I drilled vent holes (the transformer gets really hot) into the box, mounted the transformer to the bottom of the box (I think that I might add some ceramic spacers to insulate it since after letting it run for 1 1/2 hours at full power the box got sort of hot). I added the green grounding wire to the mounting screw. Finally, I added a cut off piece of extension cord to supply power to the box.
These pictures show how I mounted the dimmer and the power outlet to the box (the 2 green wires are ground wires). I used the washers to give it a little extra support. The next picture shows a white wire coming from the indicator lamp (it gets connected to the other white wires and to one of the 2 primary wires going into the transformer (I don’t believe it matters which one)). The second and third wires connect to the remaining primary wire from the transformer. The forth wire (the far right) is connected to the one of the dimmer wires (the other wire on the dimmer is connected to the houses electricity). I’ve included the next picture so you can see what a jumble the wires become. Notice that the 2 yellow wires coming out of the plug are connected to the two yellow wires on the transformer. I capped off the third wire. You can see from the picture why you need to understand how the electricity flows. I tried getting better pictures, but this was the best I could get.
This picture show the box up and running I like the fact that it is protected with a fuse. I had forgotten to put the fuse in and the whole thing wouldn’t’t power up. I hope this will protect me if I do something stupid. I used to power plug to hook up the cutting bow so that I could easily switch to different styles of cutting bows.
Cool, but we sell KRM power suppliers for $100. They allow variable voltage for different wires and wire lengths with the turn of a dial, have on and off switches and most imporant a fuse. I’m all for do it yourself but, damn, I’d worry about burning down the house with some of these things.
This version does all 3 also. The dimmer turns the power on an off and regulates the amount of power (the indicator light glows with varying levels of brightness depending on the dimmer’s position) and it has a 3 amp fast acting fuse. However, I have the same concerns you have. I certainly wouldn’t walk away with it plugged into the wall (even though it should be okay). It is nice that the whole project only cost around $30. I’m finding out that starting off shaping is very expensive (even if you cut corners).
After Greg’s concerns I felt that I had to go home and give it a try. It worked amazingly well. I don’t know what I was expecting but it doesn’t even feel like its cutting. Heres a picture of the finished product.
I’m just puting one together also, so it’s interesting to see how others do it.
The plug for the different bows is a great idea and very practical, as is the safety of puting in a fuse, something I had completely overlooked. The light is a sensible idea too.
I bought a ‘home builders hotwire kit’ from Aircraft Spruce for $28.50. (a push on-off adjustable dial and transformer unassembled) Comes with simple to follow wiring daigram. All the other vac stuff is available there too.
While the bow plug seems like a good idea, I would point out that using a 110 volt-type plug for a post-transformer-tap (12 v?) connection may NOT be the smartest thing. If someone comes along and helpfully plugs your bow into a wall outlet they are going to be in for a surprise (to say the least).
Keith is right. I’d go to Auto Zone and get male & female 12 V (car lighter type) connections.
My hot wire bow power supply is a 6V/12V car battery charger. 5 different Volt/Amp choices - enough for different lengths and guages of cutting wire. Alligator clips onto stripped wire loops on the bow. And I can still use it as a battery charger. It hums so I know its on, although I like the light bulb idea.
I never thought about somebody else plugging it in. Your right, that would not be a good thing. If I were to redo this project I would change the plug (and here I thought I was being so smart). I think my solution will be to lock it away when its not in use then change it latter down the road. Thanks for the suggestion.
Thanks for pointing that out. I don’t intend to let my gear get into the wrong hands, but hey, sometimes it’s my hands that are the wrong ones, so I think I’ll change it.
Thanks for the safety hint. An accident is usually an incident that could have been avoided.
I bought a ‘home builders hotwire kit’ from Aircraft Spruce for $28.50. (a push on-off adjustable dial and transformer unassembled) Comes with simple to follow wiring daigram.
It is my understanding that the transformer that comes with that setup is a 24vac 3amp version. I was reading up over at some of the rc groups and this is a good setup if your bow wire is not much longer than 30" or so. The guys that are really into it or cut longer wings would go with a bit more powerful transformer. Something like this setup: http://www.public.iastate.edu/~orman/air/cutter/page9.jpg
The very best to control the voltage would be the “variable autotransformer” (also called a “variac”) like Greg suggests, but even better to use the variac to control a transformer like the above drawing for more precise heat control and isolation from the full power source out of the wall outlet for safety. If going with a rheostat I read that the kind for controlling the speed of ceiling fans is better than just using a light dimmer switch.
The rc guys say that wide cuts as good and smooth as a CNC hotwire cutter can be made by hand. Most important you must have the proper wire temperature. Other key things are you’ve got to keep the wire tensioned so it does not sag at all. The wire will stretch when heated. So tension like that of an e-string on a guitar is what I’ve read. Also have your template super smooth so the wire does not catch. Formica is suggested because it handles heat better and if you stop for some reason it is less likely to burn a notch into the template that you’ve worked hard to make and it can be polished super smooth. Masonite is another good one. They go down to 1000 wet/dry on these template edges so the wire slides perfectly. Also if you have a clamp-on amp/volt meter you can use this to tell the exact amperage and have the best idea on your wire temp.
Sure all this could be a bit overkill for some. But part of the beauty of using the hotwire to me is that you could get the EPS blank cut to near finished rocker/profile dimensions in a somewhat clean environment. But you will need another person to make perfect cuts, with increments written on your template calling them out to each other along the way.
What wire you use is a very opinionated subjective thing with most of the rc guys and I think something that is dependent on if your using a long bow wire or a short jig-saw table like setup. Here is quote of one of the better breakdowns on wire that I found;
Quote:
“I’ve used quite a bit of wire on my CNC cutter…here’s what I have found to be the “best” with some of the different wire’s issues and qualities.
1 - Rene (sometimes called Rene 41)- used in commercial cutting quite a bit. Can hold LOTS of tension but is fairly brittle. Care needs to be taken when attaching to the bow b/c of the brittle issue, you can’t bend it too much or it will break. It doesn’t stretch much or at all when under a lot of tension. It takes a decent amount of power to get it up to heat but once there the cuts are VERY smooth.
2 - Inconnel - very sensitive to voltage and heat. Even a little bit of voltage can create a large heat difference. Inconnel holds heat well and is also used in many commercial cutting applications. Inconnel is less expensive than Rene and is easier to find. It holds tension well and doesn’t stretch much (but does stretch more than Rene.)
3 - Nichrome - this is what I generally use just because of it’s availability. Nichrome will stretch a good amount when heated. It’s not as sensitive to voltage/heat as Inconel is, but it is more sensitive than Rene. Nichrome is fairly cheap and as long as you retension it every once in a while it works fine.
4 - Stainless Steel - I’ve used lots of different types of SS. It works well, but I like the above stuff better. I would stick to the top 3 if possible."
Wire thickness; I still need to research that more. But it seems dependent on what type of wire you use and how long of a wire your using.
Attached is a pdf plan that one of the rc guys sent me in an email for a bow.
Hope this helps any of you that are also planning on hotwiring some blanks
I’m glad that you decided to post that bow. Its very hard to put all of the pieces of the puzzle together. So much of the information I’ve read contradicts itself. I’ve heard that .02 dia stainless steel wire is the best. I ended up using nicrome wire for my small cutting bow. Even with a spring attatched it really stretched a lot. I think that I’m going to purchase a spool of stainless steel wire. Its sold in fishing stores and is used as trolling wire.
