Cutting foam to fit stringer without hot wire?

Finn1's picture
Finn1 started the topic in Saturday, 27 Jun 2020 at 6:23pm

I'm planning on making a new board. From what I've watched most people create the stringer first then glue it between 2 pieces of foam then cut around the stringer with a hot wire. What's the best way for me to cut the foam around the stringer without a hot wire?

Itsmemickyb's picture
Itsmemickyb's picture
Itsmemickyb commented Sunday, 28 Jun 2020 at 8:17pm

Why not use one? you can make one pretty cheaply just get the people at jaycar to help you

morg's picture
morg's picture
morg commented Sunday, 28 Jun 2020 at 9:18pm

Agree with #itsmemickyb. My father used to make radio controlled gliders out of foam. Spent ages shaping the foam, then decided he’d make the Hotwire gadget (and got the bits from Jaycar). After he made a few templates he happily Hotwire carved out a bunch of them in no time.

tiger's picture
tiger's picture
tiger commented Monday, 29 Jun 2020 at 7:43am

A basic Hotwire is really easy to make. I made one up to cut blanks off a big billet of EPS. Just screwed some old offcuts of decking timber together, one piece a metre or so long, and 2 shorter pieces, screwed together to make a frame of sorts. Connected a thin wire to an eyelet on on side, and to a sturdy little spring on the other. Connect the positive and negative wires from an old 12 volt battery charger to both sides, and voila, you have a crude yet effective foam slicing machine.

Island Bay's picture
Island Bay's picture
Island Bay commented Monday, 29 Jun 2020 at 8:39am

Finn, make yourself a hotwire.

And do yourself a favour and cut two stringers, both slightly bigger than the end result, Cut your billet of foam down the middle, then pin/glue a stringer on either side of the half width and cut. Repeat with other half.

The cutting wire on the hotwire can sag a bit, which means you end up with thinner profiles. Hence the slightly wider/deeper stringers.

spidermonkey's picture
spidermonkey's picture
spidermonkey commented Monday, 29 Jun 2020 at 9:02am

Island Bay's method is a good one. I do the same except i just hot wire the intact billet with ply rocker templates pinned accurately either side. For my eps boards i never use a stringer. you also need to create deck templates, then you end up with a blank pretty close to what you want.(less shaping with the plane, sanding blocks etc). I went the lazy option and brought a hot wire from a online art/sculpture site, it works great. Never hot wire poly u blanks!

tiger's picture
tiger's picture
tiger commented Monday, 29 Jun 2020 at 9:28am

I concur with the gentleman above! The sturdy spring in the Hotwire pulls a bit of tension back into the wire, as it stretches under the heat. Still get a bit of sag, but a steady pull on the Hotwire frame keeps it cutting flat/straight. I too pin templates either side of the foam billet for the wire to ride on. I found 3" nails with a flat head work fine just pushed in by hand to pin the templates, I just used some out of my framing gun. I get the max out of my foam block by cutting my foils/ thickness flows flat, then bending the rocker in on a rocker table while vac bagging skins/veneers.

garyg1412's picture
garyg1412's picture
garyg1412 commented Monday, 29 Jun 2020 at 3:40pm

spidermonkey I'm intrigued by the deck templates. Being a bit of a hack I get the stringer templates process but can't get my head around deck templates!!! Isn't that more of a two dimensional process and if so how do you do that with a hotwire??? Cheers

spidermonkey's picture
spidermonkey's picture
spidermonkey commented Monday, 29 Jun 2020 at 7:01pm

Hi garyg1412, What i do is trace the bottom rocker on a length of ply, then mark up the deck rocker above that like you said so you have a two dimensional profile with your thicknesses just as you want the finished board to be. then cut out the deck rocker, fair it up and away you go. tricky part is positioning it accurately on the billet in relation to your bottom rocker, so you want a bit of extra thickness to be able to fair back the hotwire marks and any stuff ups etc. Once you have done a few, and get confident you can get the hotwired blank pretty close.

Finn1's picture
Finn1's picture
Finn1 commented Thursday, 2 Jul 2020 at 3:37pm

As a 17 year old I'm real broke and not looking to start anything too tricky. Everything on youtube seems like I need uncommon little pieces of electrical circuits. Im from Australia so if you have any idea where I can buy some power sources or what not let me know

Itsmemickyb's picture
Itsmemickyb's picture
Itsmemickyb commented Thursday, 2 Jul 2020 at 6:45pm

https://www.flitetest.com/articles/hotwire-template-tips

an elastic loaded hot wire like the one on the page here will help with sagging
ive got a spring loaded one but i think this will be the way to go

Itsmemickyb's picture
Itsmemickyb's picture
Itsmemickyb commented Thursday, 2 Jul 2020 at 6:50pm

hey finn a poly blank and sun cure resin might be easiest if you just want to do one and keep it simple. A hot wire and eps may cost a little more and be a little trickier to setup but then your blanks will be really cheap (like $25 ) and therefore good to learn on. up to you tho.
and watch all the Kazuma shaping videos on youtube, theyre the best haha

Spuddups's picture
Spuddups's picture
Spuddups commented Thursday, 2 Jul 2020 at 7:39pm

Some good advice here. I just mow the foam down with my planer, but I should really just build myself a Hotwire.