Hot Wire Cutting EPS.. Cut Template Big ??

Aloha , Getting ready to start a EPS board . I have made a template but wonder. Should I cut the rocker curve a little big and then sand it down to size? I know that the hot wire doesn’t cut perfectly smoothe . At least not for me . And I don’t want to sand too much and loose the rocker I had intended . What do you experienced EPS board makers do? Or what do you suggest for a beginner? I was thinking of making it 1/8th or 3/16th bigger than the template? Thanks , Don

Hi Hotcoat,

I try to make my rocker templates exactly what I want. I think that’s one of the main advantages to using a hot wire - making precision rocker. Have you tried putting a strip of masking tape along your template? I think that makes it easier to get a smooth cut. If you practice a bit you can get a perfect cut ( or at least pretty good) with the hot wire. Also getting a mate to give you a hand helps too.

Jong . Thanks for the reply. So you cut your EPS to exactly the size of your template? I have tried 1 other board . It was a XPS extruded foam and the cotter sorta “skipped” and dug it more in some places than others . The failure of that project ended up being the glue thou. I don’t really want to practice and waste eps that’s why I was gonna cut it a little big… I will try the masking tape trick THANKS for that . I will have to thing wether I am brave enough to cut my rocker exact … Aloha , And Thanks Again, Don

eps will press in to shape if you are using a rocker table

i recomend you cut the 2 templates exact size maybe a couple of mills bigger

the above template cut is easier than the below cut cuz you have the weight of the bow on your side

make your above cut the bottom of the board cuz that is finished as soon as it is cut

you have to shape the deck and rails a bit anyway so make that your below cut .

do you understand???

try not to have to shape the bottom is the best

and one of the adantages of a hotwire cutter

perfect and consistent rockers every time

have a friend hold the other side of the bow makes it shit loads easier

we can cut out 10 boards in a couple of hours

i use a 1mm stainlees wire with 12volt DC variable power suply

usually runs at about 8 to 10 amps

i thought a bout using an old computer power supply maybe

but a battery charger over 6 amps should work

u just need to try a few different guages of wire

Silly, I understand the theory of using the weight of the cutter but couldn’t I just flip the blank over doing both sides from the top and using the weight on both? I have just gotten another thought . Off the topic some . I work for the evil “home depot” here in Florida and have an Idea how to contact the supplier of the 2 inch thick EPS we get … Maybe I can get other sizes thru special order . If I can I will pass the ordering info on here … And oh yea I get the same discount there as all of you …zero… Aloha

yeah cool you can do that. i just bought foam in a massive block(cant turn it over) it works out heaps cheaper

say 25 $ nz per board

a 2 inch sheet is perfect if you got a rocker table and you are doing a cored skin cuz u can just press in the rocker and itll hold its shape after the bottom skin is on

I use to get crappy cuts with my hotwire until I saw how Airframe did it. Now mine are coming out near perfect. The main change that I made was to buy a real variac. My homemade power supply caused me nothing but grief. Its probably the best $50 I’ve spent in building boards.

It does sound like your wire got too hot on your first template cut.

smooth templates, proper wire temperature and tension and your cuts will come out smoother than anything you do with a planer. Cut top and bottom to exact size then do this trick to crown the deck. With the deck up, put a 4 to 6 in wide strip of masonite down the center, move the rail templates down a 1/2 or more to suit your taste for rail thickness, use pressure on the hot wire bow to bend the hotwire across the center strip down to the rail templates. See my bad art for a visual.

Hey Dan, Thanks for the reply . I have only tried one other time and got a crummy cut . That’s why I am thinking to cut it a little big and sand / plane it to the finished size I want . Am I the only one to think this way? I have had some experience with the hot wire other than that . I used to build house walls out of styrofoam blocks . They were filled with concrete and made strong & very well insulated homes - R-50 insulation values … Anyhow I mostly used a cutting table to cut the blocks but I feel it is real hard to get a perfect cut but others do it ?? Part of it is my templates I am sure . They are not perfect enough . I can draw the curves perfect but cutting them .(with a jijsaw) they dont come out perfect … Any tricks for that?? Thanks Aloha, Don


this is the third time my message got deleted so maybe im not supposed to tell you

cut out ist template with a jigsaw and then use a small SHARP block plane to smotth it out

sight along the edge until the curve is perfect

use that as a stencil for the second template which will turn out better on the jigsaw cut

plane the second one

drill holes

pin to foam with screws

Any place that my cut looks bad is a place where I didn’t have the template quiet right. I’ve been using 1/8" masonite, but I’m moving to 1/4" (last time the wire actually burned through the 1/8" and I made a nasty scar fixing it. I like to cut the template with my band saw, clean it up with the surform (I always loose a little skin during this phase, then hit it with sandpaper (smooth, curved edges really help). However, I never got a good cut until I bought the variac.

or better; use a bearing bit router and copy the original precisely…

after cutting and truing the first, cutting with a router (even a laminate trimmer) will have your second (and perfect copy)template done in less than 15 minutes.

and do yourself a huge favor and make the templates precise…nuthin extra.

never thought about native customs idea for deck crowning…interesting…alot less messy than using a planer, though I don’t know that I’d get the cuts I really wanted that way…

Hey , Using the router or laminate trimmer is a great idea I allready have the laminate trim bit with the wheel . I just need to try to make the first one perfect … Well here goes nothing… Aloha,Don.

i dont actually measure very much and prefer handtools

i can cut a sheet of 7 mm ply with a japanese peircing hand saw pretty fast

masonite? no probs they whip through it

alas its finally died and the jigsaw dominates the process

sitting quiely on the verandah with my sharp stanley block plane (20$ second hand)

listening to the birds

hotcoat thats funny. U got a router and table and still make messy templates


Yo Silly, Yea I’m more of a mechanical minded person . Not very artistic . Can’t even draw a straight line … But with a framing square I do fine . I have struggled thru a couple of boards and they are OK . But you guys with all the shaping talent amaze me … Aloha, Don

    here's a pic of the best board Iv'e done ... Board #2

i like the way hand tools feel with any kind of work

im a goldsmith by trade

im actually quite crap at shaping boards though ive decided

very much an amatuer

the templates,hot wire and rocker table does all the work lol

that fish looks sweet to me mate

id hate to try and shape a pu blank

i think i would stuff up the rocker for sure

i wish my fish turned out that good


hey GWN,

The hotwire deck crown method works great, but it’s definitely not for the final cut, just saves many planer passes and gives a very reliable edge to measure from for rail bands. You can also add vee to the bottom with the same technique using a narrow center strip, steady hot wire and perfect finish. If you use two eps sides with a stringer, you can reverse the technique to get a single concave started to the desired depth. I have just started thinking of the hotwire as a really big planer.

I’ve used a heavy duty exacto knife for cutting masonite. seems to work well. It doesn’t cut strait through you just score the masonite and when you’re done, the masonite just folds and viola! a straight cut. I also sand it after to get the outline curves smooth. it sands really easy. I think the router would be the easiest. But I just don’t have that tool. Exacto knife works and is cheap.