Easy Hot Wire Cutter Guide (AC Adapter, Guitar String or Nichrome)

Introduction: Easy Hot Wire Cutter Guide (AC Adapter, Guitar String or Nichrome)

About: I love the inspiring minds of the instructables community Here are some links to some inspiring people: Jude Pullen: http://www.judepullen.com/designmodelling/ Austin Kleon: http://austinkleon.com/

This instructable is different than previous ones because it uses Hot Wire Cutter Design Charts to ensure the perfect finish.

My design is simple - no tables, no springs, no dials, just the raw guts: power source and hot wire.

This instructable builds off of my hot wire cutter calculator and as a result i've been able to make hot wire design charts which will prevent AC adapters from frying-to-death and will ensure the wire is hot enough to cut foam-so you waste no time on getting your cutter up and running as fast as possible.

Disclaimer:  The wire reaches temperatures between 464°F (240°C) to 860°F (460°C). Some designs may require high current that may cause electrical shock and possible death.

*** I haven't personally built all the possible designs from these charts. These Design Charts are based on electrical theory ****

Step 1: How to Design a Hot Wire Cutter (Design Charts Introduction)

Picking your hot wire length, diameter, material, and power source will be a balancing act, but it can be done! I've found that the power source is the biggest head ache, so we will start there with an example.

***** All of the Design Charts are based on a AC to DC wall adapter. Meaning the output is in DC (direct current) not AC.*****

Example - Lets say I have an AC to DC Adapter and it can output 4 Volts and 7 Amps and I want to use a 0.012" diameter guitar string. (Don't worry, I will show you how to find these numbers and decide these numbers later)

Procedure - Looking at the Hot Wire Design Chart - 5 (on this page), I will find the 7 Amps on the x-axis. From here I will move vertically till I find the curve that represents 4 volts (see chart). At this intersection, move horizontal to the y-axis. The value on the y-axis is about 8.2 inches; this is the length of my hot wire. Rounding up or down to 8.0" or to 8.5" is best, because these curves mostly represent an average of allowable lengths which will work with this power source. In fact, you can even round up or down as much as two inches when using the lower voltages on a chart.

Results - Chart-5 is for guitar strings (steel) which have a diameter of 0.012 inches, or in guitar lingo "a 12." So, my final design would be an AC/DC Adapter which can output 4 volts and 7 amps and a 12 guitar string which is 8 or 8.5 inches.

Design Charts:
These charts I made from scratch from my hot wire calculator and programming a loop to 'trial & error' all the possible correct combinations for circuit that will get hot to cut and not fry-to-death the AC Adapter. They can be found at the end of this instructable.
Charts numbered 1-8 are for cutters using guitar strings.
Charts numbered A-E are for cutters using nichrome wire.
Each chart represents a different diameter of wire. In our example above we used Chart-5, because I wanted to use a guitar string with a diameter of 0.012". If I wanted to use 28 gauge nichrome wire, i would use Chart-B.

Personally, I stay with Chart-5 because 0.012" dia guitar string is easy to buy for a buck and is strong enough for hundreds of cuts. The best thing you can do is find an AC adapter in your house that belongs to nothing, and thumb through the Design Charts (at the end) and see which set-up will work.

What if the Volt curve for your adapter isn't on the Chart?
Draw it in. Just stay between the volt curves that sandwich the curve you are going to draw.

What if the amps never intersect the volt curve? (left of curves)
Then the AC adapter you picked doesn't have enough capacity to withstand repeated uses of cutting before it frys-to-death.

Step 2: Misc. Design Points-

Pick Your Power Source:
I always work with DC current. Batteries are always DC current, and AC Adapters convert wall AC current to DC current.
mA stands for milli amp. If your adapter says 300mA then in amps it is 0.3A

Battery source have lower risk because the voltage and current are so small.
Batteries wont fry-to-death in any of our designs, but will have a limit on how long they can last.
Battery housing can be found at radio shack

Wire Types:
guitar strings: "8" or "12"
You can buy individual strings from the guitar store most the time for a dollar.

Frame Types:
fork frame or bow is the most basic frame and is found in the hand-held cutter, table-top cutter and in the gravity-table cutter.

Frame Materials:
PVC pipe

I found the best method is to find my AC adapter at a thrift store, and review all the Design Charts to see what wire length, diameter, and type I should use.

if you want to fine tune your cutter or just see the stats of your design. Some programming was done to create a loop which

Step 3: Appendix - Steel Wire Charts (Guitar String)

Steel Wire (guitar string) Charts:
Chart 1 - 0.008 diameter wire
Chart 2 - 0.009 dia
Chart 3 - 0.010 dia
Chart 4 - 0.011 dia
Chart 5 - 0.012 dia
Chart 6 - 0.014 dia
Chart 7 - 0.015 dia
Chart 8 - 0.016 dia

Chart 1R-0.008 dia Lowest possible risk design (least voltage and current required)

Step 4: Appendix - Nichrome Wire Charts

Nichrome Wire:
Chart A- 32 Gauge
Chart B- 28 Gauge
Chart C- 26 Gauge
Chart D- 24 Gauge
Chart E- 22 Gauge

Chart AR - 32 Gauge (Low risk design. Low voltage and current designs)

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    4 years ago

    How would I calculate this if I wanted to use a dimmer switch to control the temperature?


    Reply 1 year ago

    You mean like a wall mounted dimmer for 120Vac lights? That is incredibly dangerous, because the wire will then be attached to house wiring with no isolation. A terrible shock hazard.


    1 year ago

    Thank you for posting this. I'm building a hot wire foam cutter as a Christmas present, this will be a great help.

    I love that you also included guitar strings.


    6 years ago

    Thank you for your chart. I built my hotwire cutter based on a youtube video. Based on your chart I expect the 12V 1.25 amp I hooked up to burn out rather quickly since I have a wire length of 24 inches. :)

    I tested it, it does work if i cut slowly..
    I see from your charts (if i am reading them correctly I should be using one at about 6 amps...

    I will be curious to see how soon this cheap adapter I had at home will last. Thanks to you I now have a method to estimate my power needs regardless of the size cutters I will make in the future. :)

    Many Thanks to you sir for thoughtfully providing these charts for people to use!

    So this is why my hot wire cutter isn't working: not enough amps. Thanks so much for these charts!


    9 years ago on Step 4

    Thanks Demolision Wolf, just used the charts to help get my HWC up an running.

    Transformer suggestion: 12V halogen light transformer. These have more grunt than typical electronics ones. They have 12V AC output rather than DC but this doesn't affect performance.