Hi, I’m going to throw a little something else out here... well maybe a lot of something else. I’ve been debating on whether I should but, BAW, so here goes. This also might generate some more thought/discussion… I don’t know.
This is something I learned building surfboards and skateboards. Go the other way with the foam density. I have a couple of surfboards and a skate board that has 1 LB/cu.ft. EPS and XPS respectively as the core material. The idea/theory being that the core absorbs the shear movement instead of resisting shear movement, so the skins move across each other and the soft core lets it happen. To make this work on both items mentioned the rails are wrapped with glass from the top and the bottom. The connection of the top and bottom skins to the rails (rail stringers for surfboards and sidewalls for skis) is key to managing the flex of the boards and how well they will hold together in use.
For surfboards the bottom skin is 1/16” balsa while the top is 1/8” balsa, and the bottom skin floats between the rails so the structure will have better flex characteristics. The folks that make these types of surfboards found that the board was too stiff when the top and bottom skins were attached to the rails. I don’t think that would be an issue for skis. The top skin is thicker to resist the compression forces since the materials are weaker in that direction. For skis the overlap attachment to the sidewalls would keep the top from compressing off of the ski.
The core would need to be constructed in a couple of steps. Since the core is too flimsy to work with by itself it needs some support to be profiled. I’m thinking that bamboo would be the best solution for the skins.
http://www.teragren.com/bamboo_veneer.aspx
Here is where I found out about this technique. This thread has all of the gory details to make this work.
http://www.swaylocks.com/forum/gforum.c ... 946#183391
This thread discusses more refinements to the technique.
http://www.swaylocks.com/forum/gforum.c ... st=3601026
There is a lot of stuff to read through, but the ideas are awesome. Bert has some very easy ideas to follow with some easy to make tools. He doesn’t give away all of the secrets, but gives you enough to figure out what is going on and how to develop the structure with what you have/know.
I made the skateboards first since the parts were small and cheap, so mistakes would not be too costly. It was my first time using the vacuum set up, so it made a good preflight into the surfboards. And I think that a vacuum setup would be the best/only way to build the core (EPS foam will distort/compress @> 8-9 in. HG). You could use a pneumatic press to do the rest… I think. The skins on the skateboard are bass wood 3/16” of the inch on the top and bottom.
Here are the basics of the structure.
Core top:
1/8” bamboo
10 oz plain weave E-glass or 10.5 unidirectional e-glass
1 lb EPS with bamboo or hard wood rails/sidewalls and binding mount plate.
10 oz. plain weave E-glass or 10.5 unidirectional e-glass
1/42” bamboo
Bottom
Ski construction top:
Top sheet
9 or 12 oz. biaxial e-glass
The core as described above.
9 or 12 oz. biaxial e-glass
Base w/edges
Bottom
The part that has me a bit puzzled is how to deal with the tips on a ski. In the case of the surfboards and the skateboards the ends are trimmed before the outer skin is attached and nose and tail block are installed to complete the shape. I’m not sure how the ski would hold up if the top and bottom skins were to converge and be glued together. That might add a lot of pop or return flex to the ski? Maybe trim them short and add a bit of solid wood or bamboo to the tips before the tip spacer material. Then match that to the core profile after.
I’m also still debating if the weight savings is worth the extensive process. Kind of goes away from the KISS principle, which is what I like about the home built skis.
Anyway have fun. Lots to look at and think over.
Hafte
