Hot Wire Foam Cutter

Discussion in 'General Electronics Chat' started by Qudalowsl, Apr 24, 2019.

  1. Qudalowsl

    Thread Starter New Member

    Apr 24, 2019
    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..
  2. Yaakov

    Well-Known Member

    Jan 27, 2019
  3. oz93666

    Senior Member

    Sep 7, 2010
    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.
  4. Tonyr1084

    Distinguished Member

    Sep 24, 2015
    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.
  5. Wolframore

    Active Member

    Jan 21, 2019
    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.
  6. Bernard


    Aug 7, 2008
    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.
  7. Wolframore

    Active Member

    Jan 21, 2019
    oz93666 and bertus like this.
  8. Farialar

    New Member

    May 2, 2019
    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.)
  9. Kjeldgaard


    Apr 7, 2016
    It almost sounds like the string for a cheese cutter?

  10. Ford Prefect

    Senior Member

    Jun 14, 2010
    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...
    s-l1600.jpg s-l1600 (1).jpg

    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. :)
    Last edited: May 2, 2019
  11. SLK001

    Senior Member

    Nov 29, 2011
    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.
  12. MaxHeadRoom


    Jul 18, 2013
    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.
    Last edited: May 2, 2019
  13. Wolframore

    Active Member

    Jan 21, 2019
    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...
    shortbus likes this.
  14. KeithWalker


    Jul 10, 2017
    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.