[benjhind]

Hello,

I know that there are lots of threads out there on cutting foam, but I've got a very simple idea and I want to know whether it is worth giving it a shot. I do very little foam cutting, so I'm wondering whether this would provide a quick and easy setup for very occasional use.

The idea is to use a 12V lead-acid (field box) battery, with a dimmer switch and a fuse, wired to a bow made using a guitar string.

The idea is basically so that I wouldn't have to buy a power supply or transformer. I know that the field box battery would give me very limited cutting time, as I wouldn't want to over-deplete the battery. If this setup will work, I have a few questions:

1) What size of fuse would I need?
2) Would it have to be an automotive dimmer, or would a household 120V dimmer work?
3) What length of bow would you guess I could get away with?
4) What guitar string would you use? I'd guess an electric "G" ~.017" (unwound) would work. I could also take the winding off of a larger string to see if it is a heaver gauge.

Any advice is appreciated!

Ben

[cassat]

Ben, try to keep the wire length to 36 inches. If you allow 1 inch on either side for your alligator clips, that makes 38 inch max.
Sig Mfg used to sell a little packet of wire called nichrome wire in this length for about
$5.00 You can check at the local hobby shop or google search it.

or ......you could just send me templates and I could try a cut for you.
Dave

[bear57]

A good source of cutting wire is stainless steel down rigger line, sold in sporting shops for the fisherman. I bought a roll years ago and I will never use it all in my lifetime.
A source for the bow is the good old hockey stick. This might take some searching as the newer sticks don't break as often as the older ones. At $200 a smack, I suppose they should last longer!

[moo]

Originally Posted by bear57

A source for the bow is the good old hockey stick. This might take some searching as the newer sticks don't break as often as the older ones. At $200 a smack, I suppose they should last longer!

Used to be a garbage can at the local rink

[igor_throw_the_switch]

A dimmer won't handle the current load (and a 120VAC one is useless in this case) - unless you are prepared to spend $$$ for a big wire wound rheostat. Run the hot-wire direct off of the battery - you will need to play with the length and thickness of the hot wire until you get satisfactory results.

Forget the fuse and dimmer.
36" is a good starting place.
0.017" is also a good starting place.

A hot wire draws in the area of 1.5 amps to 2.5 amps depending on what you are cutting.

Brad (mediocre 'lectrician - I don't know any good ones )

[benjhind]

Hey Brad,

I was hoping this thread would draw your attention, seeing the number of posts you've got on the subject here and on RCG...

I'm assuming this is relatively unsafe, but I dont intend to do it without extreme caution. So, adjusting my temperature, I'd want to go smaller-gauge/longer for cooler, thicker-gauge/shorter for hotter?

Any chance this will screw the battery? I'm assuming over-discharging is the biggest risk?

Cheers!

Ben

PS. Thanks as well to the others for the posts. Dave, you're always first to offer help, thanks!

[cassat]

No problem Ben,

Some guys just use one of those electric carving knives for Turkey. Thanksgiving is coming soon. Maybe you could carve a foam turkey with neon orange wings?? Sell them to the Americans for hunting season maybe ??

[igor_throw_the_switch]

Ben: You've (and I've - I did the Homer head smack afterwards) overlooked the obvious one here. Your buddy's pack is already half biffed, right? Why don't you use that AND his ESC (to control the heat via your Tx) to heat the wire? The pack is already on its' knees, right?

Thanx for the kudos.

Brad

[igor_throw_the_switch]

Originally Posted by benjhind

I'm assuming this is relatively unsafe, but I dont intend to do it without extreme caution. So, adjusting my temperature, I'd want to go smaller-gauge/longer for cooler, thicker-gauge/shorter for hotter?

Any chance this will screw the battery? I'm assuming over-discharging is the biggest risk?

I can grab onto 24 volts and hold on for dear life - and I won't feel a thing. Dunno how many times I've actually been hit by it just because you can't feel it.....

You got it right on the heat control.

Screw the battery? Sure can if you pull too much out of it. How much is too much? *ahem* I'd go with the biffed packs - who cares, right? Lead acid cells don't like repeated deep discharges......

Brad

[benjhind]

Dave...

Brad; respect where it is due. You don't know how many times you've been hit by 24V because it has funked with your frequency Just kidding.

In terms of the messed packs, I was actually hoping to build a plane for him as a surprise. I've actually gone ahead and reverted to the knife/sandpaper approach for the wings, and am going to postpone work on the cutter for future projects.

Stupid question here, but I havn't seen it elsewhere: It has to be a brushed ESC to cut foam, right?

I decided on just scaling down a trainer for this bird, building from foam and coro. I'm a bit frustrated with the lack of mid-size electric trainers out there that replicate their 4-channel 40-sized counterparts. I guess this could be for a reason, so we'll see how this thing flies when I'm done. If it is half-decent I'll post a thread on it.

Thanks all for the replies.

Ben