I have looked all over this site and others trying to find out what wire and gauge size is being used in the home made foam cutters.. And what wire gauge and temps are used for what foam and thickness.
Going back to 1970 we used nichrome wire 20-22 gauge and used a old or new model train transformer for power on are manual bow cutters..

 

Try this site: https://jacobs-online.biz/power_supply_design.htm

 

.. what wire and gauge size is being used in the home made foam cutters.. And what wire gauge and temps are used for what foam and thickness.
Going back to 1970 we used nichrome wire 20-22 gauge and used a old or new model train transformer for power on are manual bow cutters..

Starting point is what is your power supply ??? .. What is length of the cutting wire ??? you must match the two to some extent , but a wide range of wire diameters and temperatures are workable

Ideally you have a variable power supply ... Nichrome wire is good , strong at high temperatures and high resistance.

 

When I cut foam the last time I took a 9 foot length of welding wire and used my welder as a power supply. When using a length that long the wire would droop, so I had to make a swing arm and a spring tensioner to keep the line tight and straight. Worked like a champ. I was cutting those 4 foot by 8 foot foam panels, two inch thick to insulate an otherwise cold basement room. Worked like a champ for me.

 

It depends on your foam. I’ve seen large bowsaw type designs that can trace out wing profiles for RC planes and smaller ones for tiny profiles. You need to do a little experimenting once you have a PWM type power supply so it cuts without melting. There is an ideal pace that won’t make a huge mess. People are using the servo test modules (PWM source) with non brushless motor ESC to control/power supply. Obviously you will need more current with longer wire.

 

I use .005 to .023 inch Ni-Cr with a Variac feeding a 100W filament transformer with 12 V secondary. Was used mostly for beer can airplane wings.

 

Here's the site... the flight test for this ducted fan is awesome... we are working up to it... Oh BTW do not use butane to simulate jet exhaust at night... lol

https://www.flitetest.com/articles/ja37-viggen-edf-build-log

 

Back in the 1960's, I used steel music wire, right out of the hobby shop. If memory is correct, wire was something like 0.010 or 0.012 inches or so.

It takes a little more power to heat up the steel wire, but on the other hand, you can place far more tension on that steel wire. That tension results in less "Sagging" of the wire while cutting the sharp curve of the leading edge of the wing.

Power was something like a 10 or 15 Amp lead acid battery charger. The amount of heat was varied by using 10 or 20 feet of standard #18 gauge lamp cord. Just make the lamp cord shorter until you get the correct amount of heat. You will need a digital multimeter with a 10 Amp DC range to make certain you don't overheat your charger. (Or, you could just use a deep cycle battery!)

I made a lot of wings with that bow. (The bow was made out of a piece of 1 X 2 inch oak from the lumber store, with two 3/16 inch by 8 inch long pieces of music wire inserted into each end of the piece of oak. A real short spring from the hardware store connects to one of the 3/16 inch diameter music wire to provide tension for the music wire. I used something like 10 or 15 pounds tension.)

 

Back in the 1960's, I used steel music wire, right out of the hobby shop. If memory is correct, wire was something like 0.010 or 0.012 inches or so.

It almost sounds like the string for a cheese cutter?

 

I did some hot wire foam cutting several years ago, but was unsure of the type of wire I needed as some people said 'xxx' is best while others said 'yyy' is best and others said 'zzz' is best.
Anyway, I got onto a company in the UK and asked if they would send me a couple of free samples which they did without hesitation . I selected 0.417mm and 0.30mm gauge Nichrome wire.
Then I read somewhere it is possible to use Kanthal wire - you know, the stuff people use for electronic cigarettes and so I also bought some 0.32mm gauge Kanthal wire also from an eBay supplier.



At the same time, I started researching and thinking about the type of power supply to use and it seems many people were using mains (240vAC) supply with a lamp dimmer..but I thought that could be quite dangerous and then I thought about a 12v supply.
I eventually got a 12v-24v high amperage dimmer from a eBay supplier as below...


I used about 0.5 to 0.75 metre length of wire and build a rudimentary frame. I wired this up to a 12v 5A power supply but I cannot remember which gauge wire I used but at the end of the day it worked very well and safe to use without risk of electrocution.

 

First thing to get is your wire. Any resistance wire will work. Larger gauges will last longer than the thinner stuff, but at the cost of increased cutting force needed. Recommended gauges are 20-24. NiCr wire is common. Kanthal wire is just a hotter version (more alloys) of NiCr wire. ALL resistance wire will expand with heat, so you'll need a spring to keep the wire under proper tension. Connect the two ends of the resistance wire to the output of a variac and use the variac to select the heat that you need to melt thru your foam.

 

The one I built used a 18v secondary transformer and rather than use a triac on the primary as many do, I Triac-controlled controlled the secondary, it was a portable version made in the Bow-Saw fashion to keep the tension.
Max.

 

You can also use stainless steel wire:
304 or 316L wire (18% Cr/8% Ni and 18/10) it has about half the resistance of nichrome cold but resistance rises as it heats up. At 1200F/650C it's at the level of kanthal (about 50% higher than nichrome).

I see stuff like this in hobby stores for jewelry and such...

 

I made one in the early 70's using an unwound spring. The wire was 0.02" dia. I used a bow fashioned from a piece of 1" aluminium tubing from an old lawn-chair, with a tension spring on the far end. I powered it with a 12V filament transformer with a dimmer on the primary. I cut the wings of my very first successful R/C plane with it, a "Dick's Dream" with two channel galloping ghost control and a Cox .020. I still have it, hanging over my computer where I am sitting.

 

We all know the benefits of pre-cutting your wire: it is much easier to roll your wire to make it into a tight coil (on a cutting wheel), and it is easier to clean the waste from your wire reel. Most hobbyists use pre-cut wire for either of these purposes, but it seems to me that pre-cutting is used by many people to make cheap best hot wire cutter for foam, because the result fine, Try this very highly rated, especially for value, ease of use, and accuracy.

 

This exact same question was asked and talked to death almost a year ago.

 

The answer is there is no answer. It is a multi-parameter problem where you have 6-7 parameters. So, as you change one or two, the other four change as well. The only way to sanely approach the problem is to fix several parameters and calculate the remaining ones. I count, current draw, current available, voltage, length, wire diameter, wire type,... there may be others.

 

As of May 2020 this thread is a year old. By now I think the original poster (thread starter) has solved their problem.

there may be others.

Ambient temperature comes to mind.

Tried soldering in the back yard many many many years ago. The night was cool and I just couldn't get the solder to flow no matter WHAT I did. Ah - to be a kid again.

 

Ahh, got caught by the necropost monster! Thanks for pointing that out.

 

I thought that this post was familiar. Is there a way to avoid ever being notified about it again??