Joining EPS blocks to get a blank



New member here. I’ve been googling a lot about surfboard construction and found many interesting discussions in this forum. Here is what I would like to ask:


I am building a CNC mill for milling (kite)surfboards. It seems to be going pretty well and I expect to have it ready in a few weeks, so recently I started looking around for EPS blanks for my first surfboard.


I want to use insulation EPS instead of a surfboard blanks for a few reasons. 1) cheaper;  2) No need to order from abroad; 3) I think it is actually easier to mill it when you have a square block that you can fix to the table. So, the problem is… I can’t find EPS piece large enough to hold my surfboard. I’ve searched all the shops and manufacturers in our country and the longest EPS piece I found was 1200mm. If I want larger, I need to order entire block from the factory, which is probably around 5 cubic meters, which can get expensive for EPS200, plus I’m not even sure I would have enough space to store it in my garage :D 

So the question: Can I glue several pieces together to make a larger block? I know most of the boards with a stringer are glued side to side, but I would need to basically add the rocker part. Having the rocker glued to the rest of the board kinda gives me the feeling I might loose it during my first session :smiley: OK probably not, but still I thought it’s a good idea to ask about your experiences.


Yes lots of info on this subject in the archives.   Glues, rockers, linear as opposed to glueing flat. Scarfing etc.   Do a little research in the archives it’s all their.  But I will add that “Time is money”.  When you consider the time and material cost., but especially the time;  A Marko Kiteboarding blank shipped UPS might be an alternative to consider.  Such a blank would be more suitable and easier to shape.  Construction grade foam and glue lines are dicey.  You could go to all that work and then knock a chunk out of your blank the size of a shoe while shaping.  PM Shark Country.  He has put a lot of blanks together.

Thank you for your answers. Eventually I managed to get a deal for half block of eps200 foam direct from the manufacturer and they agreed to slice it as needed. Feel free to delete this thread since apparently it was discussed before.

Would rather that you continued on and lets us know how it goes for you.  Progress etc.  Maybe a build thread.  Would really like to see how it goes for you and if you are able to use any info you pick up here on Swaylocks.

All right, I will post the progress here as soon as I have my first cut on the CNC. Right now it’s just a pile of parts, too early to call it progress :slight_smile:

I haven’t been building many boards lately, but I still make with boards from EPS coolers. I may be on the last one because the meds my wife gets shipped in coolers may stop coming because medicare won’t allow that. I also used up all the larger block foam I had.

McDing is correct about the glue lines. They can tear out a chunk of foam. Sometimes I’ll use a razor and carefully slice the glue out instead of trying to sand or use a planer. I get away with it because I cover the deck with thin balsa for extra strength against pressure dents. I think a CNC machine might be able to cut cleanly over a glue line, but I’ve never used a machine. The ones that have the big round blade instead of a router would be the best.

Here’s the latest glue up I have. I only work on it when I’m in the right mood. Planning on a 7’ egg, or a square tail. I need something that can paddle as well as a long board, but short enough to throw around like a short board.

Quite a few blocks there! Did you ever consider putting them together in a brick pattern (not sure about the right term for this in English) to get more strength?

I glue up about 2 feet of the pieces then glue them to the center piece. I’ve found that having them this way is actually stronger because the glue lines are harder than foam. I cut outline a bit narrow then add a single perimeter piece to be able to make a clean rail. Lots of work to make a shaped blank, but I’m retired and we were getting these small coolers every 2 weeks. I take several months just to glue up the foam these days, and then wait until I get in the mood to shape. Then I have to be in the mood to glass and finish it. The last several have come out good and I’m happy with them. I only make boards for myself, so it doesn’t matter what they are made from.

Here’s what it should look like once it’s shaped, and then finished with a balsa skin on the deck for extra strength.

I did one with the foam running nose to tail, without the perimeter rail. It was a while ago and I can’t remember exactly why, but I think I had issues along the rail where the pieces met and it found it easier to glue up the blocks the way I do now then shape the blank with the perimeter band. The wood inserts are to support the fin boxes.

I also had blocks of foam that were only 4’ long and 11" wide, so I made a bunch of boards by joining rockered slices. I stagger the seams to added strength.

These are all just to have fun making strange boards. I have several slab cut stringered EPS blanks that are waiting. They’ll be for the more traditional boards I have in mind.

So I promissed to post my first cut and here it is!


Assembling the CNC and the table took way longer than I thought but finally I have it (mostly) working. Yesterday I did the first test of cutting a block of foam - just a surfacing operation to calibrate the stock. The next step will be to try cutting a scaled smaller surfboard sample. If that works well, then try to go full scale.


One thing I am wondering is… what 3d software is the most popular for designing surfboards these days? I found shape3d and boardcad used to be quite popular, but when I searched the forums here, it seems that most of the discussions about these apps ended around 2017 or so… are they still relevant? I have some experience with Fusion360, but I’m not sure if Fusion would be the best/easiest choice for surfboard design.


Update on the board I’m making. All the foam was glued up and perimeter bands were added. I hand shape the blank to get it squared up. This is the top before the rail bands were added. The shaping is done and I laminated the bottom, but I didn’t take new photos. I will get more photos later.

@sharkcountry that looks very cool. Do you expect the board to be as strong as the one made from a single foam block?

I usually add a balsa deck skin either 1/16" or 1/8" thick sheets of model airplane balsa. I also try to keep the laps going all the way around the rail. So far, I haven’t had issues with the boards. The balsa decks are very strong against pressure dents.

I believe the glue joints add a lot of strength compared to a single piece of foam. They are spaced just under 2 inches apart. The foam is about 1lb density, when I get foam that is softer, I don’t use it.

If anything, this process is much more complicated compared to a single block of foam. I do it because I had all these small EPS coolers coming to our house and gave away as many as I could. I believe this is the best way of recycling that foam. Sending it to a place that breaks it all up then fuses it back seems to require a lot of energy. I use a bit to cut up the coolers and a little more in the shaping.

If I was making boards for other people, I’d buy a good PU blank and do it right.

This is just something I can do with excess foam that would end up in the trash bin. I’ve made 5 now and 3 are used quite a bit.

karolis:  the best CAD software is probably the one that you’re most familiar with, and the one that exports a toolpath your machine can use.  Unuseable toolpath = useless software.  And that’s all I know about CAD/CAM.

OK so the CNC homing issues are fixed and machine is almost ready to cut. 


I also played with Board CAD, AKU shaper and a few other programs. From all the apps dedicated to surfboard design, AKU Shaper seemed like the most promissing one, but in order to use it with my CNC machine I would have to pay $45/month and still get an application with very limited features. Meh. I went back to good old Fusion 360 and after a few days of tracing the slices and outlines I have a virtual copy of my current board.


I still need to add fin box positions, cleanup the design a bit and buy a compressor to blow off the foam dust. The foam is going to be everywhere! Hopefully I can do some test cuts in the next few days.



EPS gets everywhere.

I babysit with a shop (25 liter drum) vaccuum cleaner and suck foam bits up every few minutes.

Support your blank at the ends. The foam will bend away from the cutter.

I use Shape3D on Mach3, but there are Euro involved in the S3D CAM license.

First attempt to cut a scaled down version of a board. There are some small issues but in general the concept works fine. With the current settings it would take around 2.5 hours to cut a full size kite board. I think after some tuning I could bring the time down to around 1 hour.





It is amazing to me how nice those blanks turn out once you’ve shaped them.  Impressive.  The balsa deck is good insurance.  Ever do one in which you did both the deck and bottom.  You know; just to the cutlap?

I used to put wood on both sides, but those were the compsand boards we did. Probably been 4 years or so since I did both sides. The balsa wood decks keep the pressures down.

I think the main strength is in the glass because most of the boards I do are stringerless. I do double lams on the bottom, one before fin boxes and one after the deck is done and the boxes are set. Comes out a little heavier, but not as heavy as a strong PU/PE build. I’m just about done with this one, I really hope this one does all I expect for a 7’ board.