Have been thinking about how to build a fibreglass “torsion box” (surflight style) into an eps blank to give some tuneable flex characteristics (no stringer of course). Does anyone see any problems I may have missed with the following process.
Take three sheets of 25mm (1”) eps and prepare to glue them together with inbuilt rocker (using table/floor, weights, etc).
On the middle sheet mark the outline of the board and then mark an offset line say 100mm (4”) inboard of this line.
Use a jigsaw to cut this “plug” out of the middle sheet.
Lay your bottom sheet on your floor/table, place you middle sheet on it and mark around the edge of the hole onto the bottom sheet.
Apply your glue to the bottom sheet (don’t put glue in the area where the hole in the middle sheet is located – remember you just marked it out) and then place your middle sheet on it.
Now take a suitably sized piece of resin soaked cloth (larger than the hole in the middle sheet by say 75mm (3”) all around), centre it over the hole in the middle sheet then put your “plug” on top and push your “plug” back into place.
Fold the edges of the cloth (which should now be sticking up about 50mm (2”) all around) back onto the top of the plug.
Take another suitably sized piece of resin soaked cloth (same size as “plug” outline) and place it on top of the plug.
Spread glue on the rest of the middle sheet surface (around the “plug” area), add the top sheet, weight up everything as required for your rocker and then let it set.
You now have an eps blank with an inbuilt fiberglass “torsion box”. You should be able to tune the flex fairly easily by varying the cloth or using different combinations of cloth in different areas. As long as you make sure you make your “plug” small enough that you never shape “into” it afterwards it should work fine. A little extra weight of course but boards made from eps are pretty lightweight anyway so hopefully wouldn’t be too heavy.