I see a lot of people on here using the same homemade hotwire bow. The plywood/Airframe model as I call it. Does anyone have a plan for how to build one of these? I made a bow using pvc pipe but it is just not stiff enough. I was just going to try and wing the plywood bow but i have this crazy aversion to electrocuting myself.
thanks
I made mine out out maple, lap jointed with springs for tension. I have also made a smaller one with a different setup for the tension. Inspired from swaylockers of course.
I don’t have plans for you, but I thought I could let you know that I have used a car battery charger to supply the current. I have one with a choice of either 6 or 12 volts. One big bonus with this setup is that a charger puts out DC current, which is much harder to electrocute yourself with than AC. Plus it is only 12V, not very hair raising. 
This is what my first one looks like, if you’re interested.
http://www.flickr.com/photos/johan1/61302467/in/set-654339/
don’t have a pic of the smaller one yet.
Thanks Johan, I actually do use a battery charger as a power source. my big problem is that the pvc isn’t very stiff and my cuts are way to wavy. I owe you a beer next time you come to lawrencetown.
cheers
No problem shoeless.
I might be going throught there again in august. I’ll let you know.
I made mine pretty easily out of some scrap wood, eye hooks, a spring, and an old model train transformer. I got the transformer for $10 on ebay and it seems to work well. The only problem with mine is that I need to get the spring to tension more than it currently is.
Pat, made the same one seen on sways.
a sheet of plywood cut out in the req’d. |__| shape. Make the cut between the “arms” wide enough so that the block of foam can fit between. A block is 8’x49"x39". We got our block cut in half at the plant so we had two blocks at 8’x24.5"x39". The hot wire bow then needs to take a 24.5" with a 1/4" or so to spare on either side.
|__|<24" long approx.
^
25" wide approx.
The two arms on mine are approx. 3" wide and 20 to 24" long. I used some screw on hooks along the arms to guide the wire and attach my battery charger. Spring on one side for tension. The hotwire cutting pic is from sways but mine is just like it.
Also made a “coping saw” style one for smaller work.
hope this helps
Hey thanks everyone, that is just what i needed, I owe all of you a beer next time i’m in SoCal. maybe Oct. or should you ever get lost and find yourselves here.
cheers
Ken, I really like that idea of multiple eye hooks for the spring. I’m gonna have to try that. I’m also gonna go get a bigger spring, cuz mine looks way smaller than everybody elses.
One more thing to remember is to have a fan running while making your cut. This helps keep the ends of the wire, where it attaches to the bow, cool. Without the fan the wire breaks much more easily. Be sure to hook your alligator clips to the wire nearest the foam, and not to the eyes or spring. Happy cutting!
Ken
heya Pat, bring beer to Big Sur this October!!!
here is a pic of my hotwire bow
I think my spring is a little too weak, althought I got a real clean cut. I really like having the tension adjusting hardware (see top right) (think I got that idea from glen).
I’ll add more specs tonight when I get home and can take some measurements.
I need some help with my hotwire. My frame looks something similar to this.
My foam blocks are 26", so I made the opening of the bow is somewhere around 30". I’ve rigged up the transformer and dimmer correctly–the guitar string gets red hot. However, when I begin to cut through the foam, the exposed edges of the string super heat and break within a matter of seconds.
Any ideas?
I use some of the good wire. I forget what it’s called. It’s not nichrome but some other stuff that Surfding suggested.
Either way, I think you need to turn down your heat until the wire JUST cuts through the foam. Anything more than that is too much.
Let’s copy paste this here:
