It has been a long time since my last board and the work shop is still not up and running after returning from Far North Queensland but I have started to do some thinking about the next board.
I'm still thinking along the lines of making a kit of pieces of the board that all go together during the lay-up. Pre-made rails of plastic can be done but ABS plastic where I live is just a bit to pricey. Its very convenient and easy to work with but I've been trying to come up with a way to pre-cure the rails separate from the core.
One of the motivations is that for a future build I want to try just taking the planks in the core together at a few spots with superglue. In the past when I have left large sections of the planks not glued together (only glued at the tips) it has helped dramatically reduce spring back.
So my idea is to use EPS foam sheets salvaged from packaging and cut the rail shape in there to create the mold.
I made a foam cutter from an old 30W soldering iron. I removed the tip and bent a copper bracket into the rail shape.
This iron had a temperature control on it so I played around with the temperature for cutting and hotter worked better. Also, instead of holding the iron vertically I put it on an angle and scraped the foam out much like you would scoop out ice cream. This seemed to create a smoother surface in the channel as the hot foam was 'smeared' out and filled in some of the large pore spaces in the foam.
I also put some epoxy on the foam just to make sure that it would not destroy the foam. It didn't eat it. the only untested thing is whether the heat generated as epoxy cures will be enough to damage the eps foam.
Hey Dean. Depth is very easy to control. I just clamped the soldering iron vertically between in a 10mm wide slot in a small piece of 10mm plywood. The idea will be to use the foam cutter by tracing out the core template. The ply piece sits on top of the template and the soldering iron butts up against the template.
The beauty of using EPS foam is that is cheap and you can destroy the mold easily to get the piece out. Also acetone dissolved EPS foam in seconds so you can wash the precured piece clean afterwards. There are loads of shops near our place that throw away the packaging material they have for their appliances so the foam is then free.
Ive also been toying with the idea of using the foam to create channelled surface in a precured skin. Maybe shape it with a hit wire, then coat it with epoxy+q-cell to help it keep its structure and then sandwich it between FG to create the precured bottom skin.
Have never worked with PU but epoxy doesn't cause any problems. EPS foam is used in the cores of epoxy surf boards. I also tested it but letting a small amount of epoxy cure on the demo peice. I'll going to use the tip you gave about letting the cure progress a long way before pouring it into the mould. This will help reduce the amount of heat that the foams exposed to.
I'm also trying to find a way to control the diameter of circular holes in the foam to make inserts with. This has been pretty trick to do because the iron stays in the hole for longer than compared to tracing the template outline and as a result the radius of the hole extends beyond the cutting pieces radius as it melts the foam away.
One of the reasons that I think this is a good approach for the way I build is that putting precured pieces in place requires that there be a good flow of resin from the buttom to the top and poorly fitting precured inserts and rails will help that.