# My foam cutter

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#### poormansairforce

##### Well-Known Member
The "Cadillac" foam cutter would use one of these: View attachment 109521
That's what I use on mine but I still ran it through a rewired microwave oven transformer to get 30 volts and then through a large capacitor with a rectifier to get DC voltage. This got rid of all my ripples. It's not necessary to do that but it isolates the secondary circuit and depending on your wire length you'll get resonance in your system from the 60 Hz which may make your cut have vibration marks in them. It also allows for much finer tuning of the amperage.

#### proppastie

##### Well-Known Member
Log Member
Ok, question.

On kids toys various chargeable type things (shavers etc) they plug in to a wall and convert it to say something like 5 volts right?

Can you get one that is stronger than others in volts and just cut the end off and use it exactly like the bow I made with the alligator clip?
I have up to 1 amp of these for printers.....what did you charger read in amps ......volts x amps = watts......but if the charger worked why?

#### Pops

##### Well-Known Member
HBA Supporter
Log Member
Also what I use. It was given to me. They are not cheap.

#### Victor Bravo

##### Well-Known Member
HBA Supporter
The device you need is most commonly called a "variac"

#### Jay Kempf

##### Curmudgeon in Training (CIT)
The "Cadillac" foam cutter would use one of these: View attachment 109521
Yup! Any Variac will do the job nicely. That is a particularly nice one.

My Aircraft Spruce kit I bought in sheesh 199X somewhere is still going ($20). Just a transformer and a dimmer switch. Works great. Package it up in a nice wall mounted box and use it for the rest of your life. Built a nice bow out of some scrap ply and mahogany and some screen door springs. I use .025 and .030-32 safety wire by the pound spool for cutting wire. Also a lifetime supply. My foam cutter has been running for profit and for pleasure for a LONG time. Have a CNC one in the box. Haven't gotten to it as yet. Too many CNC toys get priority. #### Pops ##### Well-Known Member HBA Supporter Log Member Started cutting RC foam wings in about 1968. When contest flying in the early 70's I built about 4 RC models I used at a time. Where I lived in western PA, there was a local factory that made billets ( 4'x4' and as long as you wanted) of foam. Cost was very, very cheap. #### billyvray ##### Well-Known Member What kind of cnc do you have. I've been thinking of building vs buying. Yup! Any Variac will do the job nicely. That is a particularly nice one. My Aircraft Spruce kit I bought in sheesh 199X somewhere is still going ($20). Just a transformer and a dimmer switch. Works great. Package it up in a nice wall mounted box and use it for the rest of your life. Built a nice bow out of some scrap ply and mahogany and some screen door springs.

I use .025 and .030-32 safety wire by the pound spool for cutting wire. Also a lifetime supply.

My foam cutter has been running for profit and for pleasure for a LONG time. Have a CNC one in the box. Haven't gotten to it as yet. Too many CNC toys get priority.

#### Jay Kempf

##### Curmudgeon in Training (CIT)
What kind of cnc do you have. I've been thinking of building vs buying.
Really old original model airplane 4 axis kit. Uses 1/4-20 threaded rods for linears and drawer slides. Not very rigid but it works. It was a friend's rig he paid way too much for it and it works but I was going to build one as well out of spare parts when it became available.

#### Aerowerx

##### Well-Known Member
Here’s my shaver plug. It says 4 volts 900 mA or milliamps. How can a person figure out how many mA is required for say a 36” line at .020” thick.

I’m the furthest thing from a electrical engineer but it just seems like this could be calculated?
Most of the available information is for copper, aluminum, and nichrome.

Use a chart like this one for copper, which tells you the maximum current capacity and resistance per foot. Your wire is about 24 guage which has a maximum current rating of 577 mA and a resistance of 25.67 ohms per 1000 feet, or about 0.08 ohms for 36 inch piece.

Use Ohm's law. Volts = Amps x Ohms, or Amps = Volts/Ohms

This means you will need Volts = 0.577 amps times 0.08 Ohms, or 0.046 volts. Another way to look at it is 4 volts with 0.08 ohms will result in 50 amps, and lots of smoke from your shaver plug!

But this is for copper wire. I would recommend using Nichrome wire, available on Amazon and eBay. Copper wire will not last long at elevated temperature because of corrosion, but nichrome is designed for that.

You are looking at it backwards. You need to know what temperature you need. I do not know what temperature you need to cut foam, but this web site has an online calculator to determine the wire size and temperature.

Note that the wire gauge size is the same for nichrome and copper.

#### Hephaestus

##### Well-Known Member
Nichrome is actually locally sourced fairly easily. Vape shops all stock it for building coils.

Believe my last 100' roll was about 10$. #### Bill-Higdon ##### Well-Known Member Nichrome is actually locally sourced fairly easily. Vape shops all stock it for building coils. Believe my last 100' roll was about 10$.
Wire A Head sorry old Spider Robinson pun

#### Slars

##### Active Member
I used stainless steel safety wire for my foam cutter. I had a step down transformer with a light dimmer. Worked great

#### tr7v8

##### Member
HBA Supporter
I used a 12v car battery charger when I was cutting model aircraft foam wings, then you could buy nichrome wire from model shops for the bow. Used top pull about 2-4amps on a 30" cut length bow. I cannot see why you would need to rectify or smooth the output. And yes I know the car battery charger is DC.

#### billyvray

##### Well-Known Member
Here is mine as described above. Plastic coffee can, dimmer, transformer, cord plug. Transformer from Radio Shack back when they were still around - can find them out there around \$12.

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#### Jay Kempf

##### Curmudgeon in Training (CIT)
The coffee can is genius. I built a wooden box.

#### poormansairforce

##### Well-Known Member
I cannot see why you would need to rectify or smooth the output.
Only needed if you're running an AC system and you have ripples and want to get rid of them. Like I said not necessary on a one-off if you can deal with it.

#### TiPi

##### Well-Known Member
Log Member
I'm using an universal power supply that has independent V and A adjustments. I found that using this variable regulated power supply works best as it provides a couple of big advantages:
- Voltage can be adjusted to suit different wire gauges and lengths
- Amps can be limited to prevent overheating when not cutting
- When cutting, the amps increase with decreasing wire temperature, giving you more cutting power and a smoother cut (with a set DC voltage)

This is what I use as my multi-use power supply (also works constant current or constant voltage battery charger, power supply for anodising aluminium, drives all sorts of electric motors for testing and variable speed projects): 0-36VDC 0-5A Slimline 80W Lab Power Supply | Jaycar Electronics

#### User27

##### Well-Known Member
How do you know when the wire is hot enough? Is it a matter of trial and error?
If it drags too much turn up the power...?

#### billyvray

##### Well-Known Member
How do you know when the wire is hot enough? Is it a matter of trial and error?
If it drags too much turn up the power...?
I usually pick spot for a test cut on the part somewhere and adjust based on kerf and wire speed. Kind of a guess. Maybe someone knows a better way?

#### wsimpso1

##### Super Moderator
Staff member
Log Member
The "Cadillac" foam cutter would use one of these: View attachment 109521
I came up with an older school Variac a loooong time ago, no switch, do digital readout, just knurled phenolic nuts for wire connections works great. I have worked with hot wire saws anywhere from 54" to 14", different wires too - used nichrome for the big saw to reduce wire sag - and the adjustable output allows you to get about the right amount of wire heat with the different resistance wires.

Oh, and the wire expands as it gets hot, so I have found it useful to make my saws like a bucksaw, with pivots on the arms, little eyebolts and cable eyelets and cable clamps, a 1/16" cable and a turnbuckle to get tension high with the wire hot, then take tension off when I turn it off. Otherwise it is trying to stretch your wire and/or break your frame when it cools. Here's my shorty.

Billski

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