EPS over 8’ is an issue primarily getting longer stringer materials. I can get access to plenty of common 1 x whatever size Basswood planks – good quality. Question, how to cut 3/16 thick stringers without specialized equipment. Looks like a typical longboard stringer needs to start with a minimum 7" wide plank width to cut shape. Cheers
I’m afraid you WILL need specialized equipment. At least a very good bandsaw and a very experienced guy to cut 1/4" out of your 1" board. Especially with a 7" or more width and a rather long length. Then you’ll have to plane these 1/4" slices down to 1/16". Can’t think of any other way to do it…
I can deal with a band saw and a planner. Are we talking a horizontal thickness style planner?
Shine…lemme guess. You found EPS, but the supplier won’t machine it. You found someone who can CNC surfboards, but the boards need stringers for the machine to hold on to. You’re going to buy blocks of foam, split them, install the stringer, and have them shaped on the machine?
There’s an easier way. You only have to split the stringer to thickness, not cut the profile. If you bring a 7’ x 7" x 24" block of eps with a stringer installed, made of a rectangle 7’ x 7" x 3/16", the shaping machine can cut away the stringer just as easily as the foam… 
Wonder how many dozens of us are trying to figger out this same stuff, all across the country right now…
Negative on the shaping machine. I’m on the east coast – just giving up stone tools and pagan rituals.
I’ve posted this before, but it fits here. An easy source for longboard stringers is the beveled cedar or redwood siding that can found at any lumber yard or home depot etc. Its usually 3/16 on one side and 1/2 on the other, 8 inches wide and lengths to 16 feet. Send in through one of those bench planers and take the bevel out to get a nice 3/16 stringer. I did this because sliding 10 foot of plank through a bandsaw by myself just didn’t sound fun.
Shine,
If you can bandsaw a 1x plank in half, fine. Then, yes, you want to run it through a thickness planer (horizontal type - either benchtop ala Dewalt type or a floor model beast ala Powermatic industrial type machine).
I would caution you though that when thickness planing to narrow dimensions - like under 3/8" +/- depending on the machine - they tend to start tearing the crap out of the plank due to the pushing and flexing of the piece as it runs through the machine.
What I do as the piece gets thin is switch to using a backer board under the thin plank (assuming the blades are on top). Something like a piece of 1x stock as long and wide as your stringer piece. Just set the depth on the machine to compensate for the additional thickness and run it and you’ll stand less of a chance of ruining the piece. Also, don’t get anxious and try to take off too much material at once. That also leads to tearout. Better to make a few extra shallow passes - just like planing a blank. And run the machine slower if it has speed control.
Also fun to try - I’ve used the full 1x even 5/4 cedar and 2x balsa and chambered them after cutting the rocker profile. Lightens them up and looks great.
Good luck - Pete
I’m one of the dozens trying. I’ve actually found an EPS company with a new CNC machine here in Montreal, just needs me to send him a CAD type file and he’ll do a test for me. I think I should be able to do this with the APS3000 software.?
It’s hard to find a place that has more than 2# density foam though. There is one that does 2.4# … sometimes. I’m going to talk with the rep and see what kind of demand he would need to tool-up to do 2.5# or 3# regularly.
I’ve already planned to get at least a 12" x 48" x 96" block of 2# after the holidays for hotwiring. (200$ CDN if you’re wondering)
What is a good stringer thickness for 2# EPS anyway guys? I’ve done a few of 3/8" for 3 test boards I’m working on right now. (HD foam)
Oh, and yeah, you do have to pay attention to the wood and planer when it gets to 3/8", one of them got a little ugly when I tried to go below 3/8". You can do it though.