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Hot wire Foam Cutter question


Paul Harris 5
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I have used printed circuit board from maplins - bit expensive and only as big as 300mm but easy to get. I've tried aluminium insulating tape over cardboard - works ok for first few but easy to damage. Someone said that they use Pertinax / Phenolic Sheet 0.5mm on RCgroups I think - this looks easy to cut and long lasting so may try this next time.

>>

I think PCB used to be made out of paxolin - but has been banned as the dust is carcinogenic.

>Hmmm... just looked up dust from cutting Phenolic Sheet --- is also carcinogenic. >

Hmmm... may go back to aluminium.

.

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  • 3 years later...

Adding some more stuff to this ‘old’ thread (originally posted on the ‘Spatman’ thread

OK, so here are some photos of my setup which copies things used by others that I found on YouTube. I made most of it from bits of scrap I had laying around, the only things I bought in were the main pulleys and the cutting wire (Nichrome 28 gauge).

The bow frame using a tourniquet for tensioning the wire. I started by using some elastic luggage straps but they didn't give it enough tension and the wire bowed when cutting.

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When cutting the frame rests on the board so I made (3D printed) a couple of wheels so that it could move smoothly. I plan to surface the board to make it smoother.

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On the end of the board are 2 plates on which are mounted the pulleys to route the pull cord down to the pivot weight bar.

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I attached some swivel links to teh ends of teh pull cord so that they can be easily detached when I want to do 'free hand' cuts.

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The next shot shows it rigged up with the frame fairly well back on the board. I need to make a hold back to retain the frame, a battery serves this purpose at the moment.

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This is the pull cord weight which is adjustable. I can also separate the 2 pull cords to position them apart in order to carry out taper cuts.

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the pull cord quick release attachments.

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The bow frame running wheels.

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When cutting an airfoil I put some lead weights on the bow frame arms to ensure that the hot wire follows the profile end plates.

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My DC power supply.

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I've tried different foams. The first I tried were odd bits of packaging, the white polystyrene type. This cut really well on low power settings and gave a nice clean cut. Off cuts from model 'plane kits (the leftovers from veneered foam wing!) cut really well as you would expect and again required low power settings and also less weight on the pull cord weight bar. Next up was some Kingspan insulation board I ordered from Wickes, oh dear what a mistake it will not cut and made a horrible smell! Lastly the grey foam board that I eventually cut the wing cores from, this was supplied by Bluefoam.co.uk and is a very dense foam which cuts really well but I had to up the voltage to 18v and I needed double the weight on the weight bar. I'm going to get some white polystyrene boards in to compare the finished article but it will have to go some to beat the grey board.

The interesting thing is that I was going to veneer the foam cores but the grey board is so dense and smooth that I'm going to use laminating film directly onto it. I tried it on a scrap bit of board and it can really take a lot more heat than white foam can and on my test piece I got no crock skin look. I'm going to glue on balsa leading edges although I could probably get away without them as the edges of etc foam are quite firm even before laminating them.

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Looks good and definitely on my bucket list of projects.

Doc, can't see any reason why the pulley / swing arm / bow suspension mechanism needs to be a permanent bench fixture - surely it could be bolted on when needed and then removed after cutting a project's worth of cores?

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  • 2 months later...

Well well well, I too am just at the experimentation stage ( again, over 20 years ago was the first time, c/l wings out if white foam packing case scrap stuff ) and purchased a roll of nichrome wire from expo drills and tools, 1 metre lenght and very thin gauge, Amati art no. 804.

 

I have some stepper motors but no driver, yet.

 

Will read this thread from the begining as well as some modelling mag articles.

 

Reason, balsa is getting expensive. Yellow PCB board for dormers, so no "wire sticktion" or jerkyness, may have a roller to roll over former...

 

As said at the experimentation stage again. Need to illuminate the "wire drag" and profile change in aerofoil section in the middle of the wing.

 

Hope stepper motors geared down will help with that problem.

 

Guitar strings ?

 

A cool but hot enough Lazer may be the best ? But money needed for that I fear....

Edited by Rich Griff
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This is by far the best wire for foam cutting, it's specially made for the purpose. I recently got a reel of this stuff and it's immensely strong and thin. I made a 1m long bow with some carbon fibre tube I had lying around and sprung it with a bungee strap. You can run it at red heat if you want and it doesn't loose strength even at high tension. I used 18 gauge aluminium templates and it is no noticeable heatsink effect. being very thin it cuts a breeze through a large block of EPS. Anyone serious about hot wire foam cutting should seriously consider using this stuff.

 

https://www.ebay.co.uk/itm/321161359058

HotWire.JPG

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  • 3 months later...

I use a homemade setup a

little like Ron Gs. Differences are, instead of wheels,

my cutting bow is held off of the table with a pan head bolt that rides on a piece

of glass for almost no friction. 
 

I also use a Variac transformer for voltage (current/heat) adjustment. I usually use around 24vac when cutting. 18 in. wire. Can’t recall

wire size at the moment. 

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I used this cheap 96W Universal AC/DC adaptor 12v-24v computer charger power supply for my hot wire foam cutting (£9.99p). Worked perfectly on polystyrene foam at any rate. I set it to 19v by trial and error on my 1m, home made cutting bow. I also used Rene 41 wire which is far superior to nichrome wire. An 8 x 4ft sheet of 50mm foam cost £17 from B & Q and I managed to get one without 'black bits' in it! It is a great way of making wings, especially if you cover them with brown paper/PVA.

 

Edited by Piers Bowlan
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