Hey Mataco,
just found this thread. I want to to exactly the same Thing for my next board. Only I will do it with Corecell. Theoretically it should work the same.
Can you give me some hints how to do the thermoforming? Where do you start with the forming. In the middle or at the ends? Do you perform some kind of cutlap or do you sand the bottom flat after pressing the topsheet? If doing foam Skin top and bottom, would you put on the bottom first or second. My Intention was to do it the following way:
hotwire rocker and outline
-press bottom sandwich with inside glass on rocker bed
-shape deck and rails
-thermoform deck sandwich
-press deck sandwich with inside glass
-nose and tail blocks and final shape
-outer glass and finish
satch, I don’t know how Corecell will take thermoforming I had some and it was much stiffer than Divinycell. The Divinycell was easy to snap if you push too hard. I used 1/8" thick Divinycell anything thicker would be too tough to form. I tape the nose and tail in place as they try to move when you form the rails. Also, put weight on the top to hold it in place. Started in the middle and worked a little on one side then the other. Use a scraper to get the tape to stick really good, its a pain when it pops loose. I found out the hard way that the foam will melt if it gets too hot. Only use the heat gun on the top of the Corecell. The amount of lap is critical too the forming too little and it won’t lap as the edge gets too stiff, too much and it won’t want to fold around the nose and tail without too many relief cuts. I put on the under glass first so I had something to push against (not denting the foam). I have gone away and came back and gone away from this method because it was impossible for me to do it without having voids that needed filling and being very difficult to keep the original shape. The board rides great but I won’t do this construction method again. My new method is much easier to get a good shape and also very strong and light. See it here.
i already have the 3mm Corecell, so that is a given. I could go with Perimeter rails made of blasa or structural foam as well. But I don’t really want to go that route.
I performed a few thermoforming tests with the corecell. It worked alright. I just wasn’t sure about were to start thermoforming the board. I’ve found a few sailboard making videos which show the thermoforming step pretty good.
What do you mean by voids that needed filling? wobbles/dents in the shape that Need filling after the Sandwich was on?
My biggest concern is to damage the EPS while thermoforming. Maybe I’ll do a few more tests and try to come up with an insulation material between Corecell and EPS while thermoforming. I’ll post a build thread but it’s not going to be to soon and it will be a rather slow Project.
There were voids where the higher density foam either didn’t get vacuumed down well and at the relief cuts. Sometimes they were filled with epoxy which made sanding difficult to get the shape smooth when doing the final prep for outer glass. Sometimes I found the foam had not set all the way down under vacuum (run your finger over the foam and it sounds different) and had to get it to bond afterwards. I used a combo of epoxy with tape pulled tight and two part expanding foam poured in and then taped. Don’t expect the vacuum to be strong enough to pull it down. The learning curve is slow on this I did probably 5 boards and felt like I was just getting the hang of thermoforming. What’s the density of your EPS? I would recommend a dry lam of glass over it before trying to form the foam.
FYI, I did one board where the foam had no paint and one where it had cloth inlay and both suffered from a darkening of the high density foam from exposure to UV light. I don’t know how Corecell does with UV.
