Would it be possible to make a solid bamboo core?
My local wood supplier has the right size planks for it.
and they're kinda cheap- about 7 bucks a piece
what are the downsides of using a solid core?
Solid bamboo core
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most ski builders use wood strips for a couple reasons:
-its easier to get strips w/o knots than planks w/o knots
-you can mix woods so you have a light core where you dont need screws
-slight grain direction differences help reduce warping where the core gets thin (doesnt matter once its pressed though)
as far a strength benefits, some people will say that its stronger to rotate the strips 90 degrees from how they are cut off the plank so that the lateral grain is now vertical. i actually just did an FEA project on ski cores, one made from a solid piece with radial cut facing up (like a 2x4), and one made from rotated strips with the lateral face up. The longitudal grain is so overwhelmingly more important to the flex and strength of the core, there is literally NO measurable flex or stress differance on an orthotropic model. the only real problem is its tough to find a 6" wide plank thats all clean!
-its easier to get strips w/o knots than planks w/o knots
-you can mix woods so you have a light core where you dont need screws
-slight grain direction differences help reduce warping where the core gets thin (doesnt matter once its pressed though)
as far a strength benefits, some people will say that its stronger to rotate the strips 90 degrees from how they are cut off the plank so that the lateral grain is now vertical. i actually just did an FEA project on ski cores, one made from a solid piece with radial cut facing up (like a 2x4), and one made from rotated strips with the lateral face up. The longitudal grain is so overwhelmingly more important to the flex and strength of the core, there is literally NO measurable flex or stress differance on an orthotropic model. the only real problem is its tough to find a 6" wide plank thats all clean!
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Motherhucker
- Posts: 10
- Joined: Mon Jan 28, 2008 7:42 pm
Take a closer look at the "solid" planks... I can pretty much guarantee it's already laminated. Bamboo culms are filled with pulp inside so the only useable "wood" (I don't know if it counts as wood because it is a grass) is the outer ring. This is cut into strips, probably 1/4"-1/2" then laminated in various ways to make a plywood. You want a vertical laminate with no veneers on top or bottom. What size are the planks? If its $7 for a full ski length board, that's incredible. Are you sure it's not $7 per board foot or something? Bamboo is way lighter than any other wood you'll find that could be used for skis (pretty much). It is, however a lot easier to bend, so you'll need additional composites, etc. to get the necessary rigidity. At $7, I'd definitely try them out... shape a core, do some tests on it and post what you find. Oh yeah, and it should come in plastic or something... keep it in this with something on top because it tends to warp pretty bad, should be fine once pressed though.
Last edited by camhard on Fri Feb 01, 2008 11:22 pm, edited 1 time in total.
BAMBOO CORES
Kingswood uses bamboo for their cores: www.kingswoodskis.com
I am currently building two pairs of skis using vertically laminated bamboo. I started with 6 foot flooring planks that were 16mm thick. A box of the stuff cost $60 and will make eight skis, so it's rather cheap.
My cores have black UHMW sidewall material epoxied in place are are now planed smooth top and bottom, ready for profile shaping. They are 14.2mm thick:
The camera lens distorts the image, the skis are truly symmetric.
The bamboo really puts a strain on my Delta planer. This stuff saws and sands easily, but the planer has a difficult time with it, even using new knives.
Like my first three pairs (poplar + spruce), these will be 185cm, 137-100-125mm, 25 meter sidecut. These will have unidirectional glass layers in addition to the usual tri-axial fabric. I use QCM resin and a heated pneumatic press.
-S
I am currently building two pairs of skis using vertically laminated bamboo. I started with 6 foot flooring planks that were 16mm thick. A box of the stuff cost $60 and will make eight skis, so it's rather cheap.
My cores have black UHMW sidewall material epoxied in place are are now planed smooth top and bottom, ready for profile shaping. They are 14.2mm thick:
The camera lens distorts the image, the skis are truly symmetric.
The bamboo really puts a strain on my Delta planer. This stuff saws and sands easily, but the planer has a difficult time with it, even using new knives.
Like my first three pairs (poplar + spruce), these will be 185cm, 137-100-125mm, 25 meter sidecut. These will have unidirectional glass layers in addition to the usual tri-axial fabric. I use QCM resin and a heated pneumatic press.
-S
VERTICAL
Vertical.
There really is no grain in bamboo. The boards are comprised of many rectangular strips of bamboo turned on edge and glued together. These strips are cut from the tubular shaped bamboo shoots. Each strip is approximately 16mm x 5mm in cross section. The strips are stacked together and glued into a board. Bamboo has "knots" along its length caused by the natural "bulkhead" features of the plant. These knots are distributed at random within the board.
I've successfully planed tapers in these cores and will post pix soon. This stuff is quite tough. Required multiple passes through my planer cutting just .015" per pass. Within the bamboo "board" there seem to be a few defects which are exposed by tapering. These are areas of delamination but should not pose a problem during ski lay-up.
Also, the tapered cores tend to warp and curl a little because the innards are now exposed to air and are drying. After making a taper, I learned to clamp the core down to a flat surface while the moisture content equalizes.
-S
There really is no grain in bamboo. The boards are comprised of many rectangular strips of bamboo turned on edge and glued together. These strips are cut from the tubular shaped bamboo shoots. Each strip is approximately 16mm x 5mm in cross section. The strips are stacked together and glued into a board. Bamboo has "knots" along its length caused by the natural "bulkhead" features of the plant. These knots are distributed at random within the board.
I've successfully planed tapers in these cores and will post pix soon. This stuff is quite tough. Required multiple passes through my planer cutting just .015" per pass. Within the bamboo "board" there seem to be a few defects which are exposed by tapering. These are areas of delamination but should not pose a problem during ski lay-up.
Also, the tapered cores tend to warp and curl a little because the innards are now exposed to air and are drying. After making a taper, I learned to clamp the core down to a flat surface while the moisture content equalizes.
-S