Just a question....

General Discussion
1

Ive been reading the archives nonstop the past couple days for hotwiring setups. I found one that i liked and want to try. Here is the post…

“ One of these days, when I have time, I’ll post pix of my crude setup. Anyway, here is how I made a simple but effective setup. Take a piece of 3/4 inch plywood and cut a big U with about 26 inch clearance across and 12 inches deep. Screw two eyebolts into each side of the wide opening in the loom. Attach 30 gauge NiCr wire to each eyebolt. Then, take an old extension cord, lop off the female end, strip the insultaion a few feet, strip the ends about one inch, and attach the black wire to one eyebolt and the white wire to the other. In the middle of the extension cord, wire a light bulb socket with a 200 watt light bulb. Make your cross section templates out of thin plywood or door skins, plug in, and you should be cutting slowly but smoothly. If you use another gauge wire then adjust your resistance accordingly (increase or decrease the wattage of light bulbs. You can always wire more bulbs in series to add resistance netting a hotter wire. To do the stringer cut, I use a saw with a fine tooth pull saw and then run each side through a woodworking jointer to make a perfectly smooth and perpendicular cut. However, you could just saw and make a pass on each side with your planer. Cheers, Gary Geist”

The only part that i dont under stand is how to wire a light bulb socket to thee extension cord. Ive anyone has any input on how to do this, or maybe a picture of it i would greatly appreciate it.

Thanks again

You guys are always a big help.

2

I’d strongly encourage you to regulate your voltage somehow. 110 V / 15-20A (house current) can kill you.

I use a car battery charger, so my hot wire is running 12V/6A.

Others use model train transformers, low voltage light dimmers, or hotwire-specific resistors.

Otherwise, the plywood bow & screws & everything are good. Well, its also nice to have a spring-loaded arm so when your hotwire stretches (they all do when hot) the bow takes up the slack.

But please don’t expose a bare 26" wire with 110 volts! One sneeze and your wife finds you on the floor 4 hours later.

3

I agree with Benny. If you don’t know how to wire a light bulb socket to an extension cord, you really shouldn’t be messing around with house current… you’ll be much safer with a transformer. Find an old model train set or battery charger and go from there… Safety first!

4

My remarkably crude setup:

a) the attachment, where the nichrome wire attaches to the electricity. Small carriage bolts plus brass wingnuts and rubber washers. Someplace in here a small spring plus an insulator would be good, as the nichrome tends to lengthen some when hot. This makes for some funny shaped curves in the cuts. Don’t use too strong a spring, you can pull the wire too thin and it overheats and breaks. Somebody who was really feeling clever could maybe adapt the string tensioner off a guitar…

b) The little torpedo level, handy for freehand work.

c) Transformer- a 6.3 V x 6 A ( roughly 20 watts) model intended for doorbells, a hardware store score. A little light on zip, but it was the best available.

d) tough to see, Nichrome wire, the gauge of which I have forgotten.

e) hand-hole for freehand work. This little gizmo can also be clamped or set in a bench vise - a table can be dreamed up to go with that so it can be used not totally unlike how you’d use a band saw.

Body is of relatively light plywood, no thicker than 1/2", this one is kinda small, limited by the size of the transformer and how much wire it can heat up. The absolute nutz would be a variac or electronics power source of up to 50-100 watts capacity, so the wire length could be varied for what ya need at the time, be it ripping big billets of foam or just fine work with a small length of wire.

Note that the conducting wires, transformer-nichrome, are fairly heavy gauge. best to use your watts to heat up the nichrome wire, not the conducting wire, and at low voltage like this it can most definitely happen.

There should be, and isn’t, an inline fuse, for those occasions when we discover that I am a far better conductor than , say, plywood or foam. Fuse holders and Buss automotive type low voltage fuses are available all sorts of places.

hope that’s of use

doc…

5

Im too in the middle of building a hotwire cutter but ran into a problem…Does anyone know where to pick up NiCr wire? Ive searched everywhere and can’t find any. My setup is pretty much the same just waiting on the wire. Ill post some pics when its done. Thanks

6

If you would like a good transformer,40 VA/110v/24v,which makes for quik work,rather than 6VA let me know,still super hot and safe.

7

Try http://www.wiretron.com/ a handy set of tables at http://www.wiretron.com/nicrdat.html for use in matching your wire to your transformer. 1-888-WIRETRO (947-3876) in US, Canada, Virgin Islands - I was given the wire I am using, but I am given to understand that’s where my buddy got it.

For what it’s worth, I took the dial calipers to the nichrome i have been using in the gizmo pictured earlier - got roughly 0.0225" or probably 23 gauge wire, 15" long between terminals. According to the tables mentioned above, my 3A transformer should be able to crank that up to circa 400°F ( being as I suspect the tables give amps per foot of wire , not for ‘any length’ and this is 1.333 ft of wire) .

If I had to do it all over again, I might have gone with the next wire gauge smaller, maybe even two gauges down and a resistor in the circuit. Especially if I wanted to ‘rip’ full 2’ x 2’ billets of foam to rocker shape. Then I could use heavier wire with the same transformer for the shorter lengths used in , say, cutting outline shapes, etc.

hope that’s of use

doc…

8

After trying steel wires of various types like guitar strings and wire used to make staples which worked but not very good I took the NiCr heating element out of an electric kitchen appliance from the local Salvation Army type store. I straightened out the wire and hooked it up to the frame which looks like a bow saw. It works great.

Joe

9

OR you could buy one at a hobby shope for what it cost to make one.

10

Thanks to both JoeMarrah and Doc the information was great, i think im going to try the cheaper way of dismantling a heating element instead of dropping $40 Can. on wire. If anyone else has this same problem try www.omega.com or www.omega.ca for a canadian supplier, they seem to have reasonable prices. Thanks Dave

11

Hi Dave,

if you can find one of the old, old toasters in a junk shop, you may be able to get straight nichrome wire out of it rather than the coiled wire you find in a lot of heating elemsnts. Or something similar.

Then, use an ohm-meter to find the resistance of the length you want to use and that’ll give you a good idea of what you need to drive it in terms of voltage vs current.

hope that’s of use

doc…

12

Thanks Im going to try rip apart a toaster, but I did come across the fact that you can use Stainless Steel wire and the result seem to be ok. Are there any probelms with using it, Im just thinking along these lines because it is readily availible. Dave

13

Ahmmm - good question.

About the main difference is that stainless steel is a bit better conductor than nichrome. That is, as the electricity passes through the wire , ( for the same diameter wire ) the greater resistance the more it heats up for a given current. So, to heat up a stainless wire to the same temperature you’d have to run more current through it - which in turn means a bigger transformer, etc.

Melting points about the same, dunno quite what the relative change of resistance with temperature is or where to look it up. That can be a problem- your wire heats up, the resistance increases and then the heat goes up. With nichrome it’s in the 2-4% range for the temperature range you’d want to deal with.

Anyhow- that’s about the info I could glean from http://www.wiretron.com/nicrdat.html . Don’t have any ‘resistance per foot/temperature/wire gauge’ tables handy here, so I guess you’d just have to do the math - your wire size in stainless would prolly be related to the diameter of the appropriate nichrome wire through the equation

DNichrome x 438/650 =DStainless

although…

hmm - the thing is, you’re heating up the whole wire, so it might be related to the cross-sectional areas. That is,

the cross sectional area of the nichrome wire should be 650/438ths of the cross sectional area of the stainless wire that you’d want to heat up to te same temp.

Or -

Pi x (Dnichrome/2) squared x 438/650 = Pi (Dstainless/2) squared

divide both sides by Pi and take the square roots of both sides-

and you wind up with

Dnichrome/2 x 0.821 = Dstainless/2

mess with the appropriate stuff from the tables I mentioned above and you have it. For instance, a 16 gauge nichrome wire, well, you should be able to substitute an 18 gauge stainless wire.

Or, make life easy. See if there is somebody nearby, an appliance repair guy or an aircraft model shop or club, who has some of the nichrome wire they will sell ya. Let me look around to see if I can find the roll of the stuff I have too… that could be quite a project in itself…

hope that’s of use

doc…

14

Here’s a link to how I made my power supply. I’ve only used it once so fare, but it did a great job http://www.swaylocks.com/forum/gforum.cgi?post=193762;#193762 I read on the charlesriverrc.org site that the stainless steel wire was better. I tried the NiCr wire and next time I’m trying stainless steel wire. You can use fishing leader wire for big game…

15

I’ve got no idea about electronics or engineering, but looking at the hot wire cutter in the photo, it looks like it could work remarkably well with a few modifcations in a profiling machine, at least to match a rocker profile? Has anyone done that before?

16

I just use stainless wire. When my bow was 28" wide, I used 22 ga. Now that its 16" wide, I use 20 ga. 6V/2A from a car battery charger.

17

Thanks doc thats awsome information you put together im definitly going to try both wires if i can get my hands on the NiCr wire. Ill post the pics when im done if anyone else who is having problems. Thanks Dave

18

Me and my friend finally got the hotwire cutter working, we used stainless steel wire, three lightbulbs, and a dimmer switch. It works great, thanks for all the help guys.