:: View topic - Mixing wood in cores

I am wondering what kinds of patterns and philosophies folks have on mixing wood in skis. basically where do you put the hardest wood and where to put the softer wood?

I want to incorporate some lighter weight wood into my cores. My goto hardwood is hardrock maple, but an entire core can be fairly heavy. i am going to try yellow cedar as my softer wood.

So my theory is: keep the bindings drilled into the maple. i think if the bindings were drilled into both maple and cedar that would be okay too(like on a glue joint)... but i would be weary to have them drilled only into cedar.

skibuilders says to use harder wood underfoot for power transfer.

Here are my current philosophies:

1.hardwood for sidewalls

2.hardwood for binding retention

3.softwood could run entire length directly in middle of ski

4. softwood could also run length in between binding strip and sidewalls, depending on how wide the ski is.

I have seen folks do butt joints before too and put softer wood near the tips and tails. i kind of like this idea because then you can have all hardwood underfoot. but i am a little skeptical of butt joints, although a good V pattern means that there is not much reliance on the butt joint. But you are still breaking up the longitudinal grain pattern and possible creating a point of weakness!

ideally my process would be more robust and i could use binding inserts, but i dont have the capabilities to align my cores well with my bases (at least with any sort of tight tolerance) but that is getting off topic

I agree with everything you have said here. I have never used cedar though and usually stick to pine and poplar for my lighter woods because I can usually get it easily and free or cheap.

I haven't done any finger joints because I am not as concerned with weight but I think they will be fine. Praxis is now doing them selectively.

I recently did a poplar core with only Some maple strips fingerjointed under the binding mount. This core weighted out at 1lb 13 oz once profiled with a cherry stinger+ ptex sidewalls. Waist thickness was 10.6mm tapering to 3 mm in the tip. The tip/tail will get hand tapered down to 2.2mm.

I've butt jointed/ finger jointed only one other core and it held up fine. This one will be a real test for me to see how well a core like this holds up.

I'll be reinforcing this core with 19 oz glass, carbon tow to and bottom and a diamond shaped mat of 19 oz on top of the binding area.

I also agree with DD, you've got the right ideas.

Here are my current philosophies:

1.hardwood for sidewalls

'the species being used is important. How well does it respond to crushing, how porous is it, how does it age/respond to weathering?'

2.hardwood for binding retention

'broadly speaking, higher the density of the wood, the better the screw retention'

3.softwood could run entire length directly in middle of ski

4. softwood could also run length in between binding strip and sidewalls, depending on how wide the ski is.

Placement of different densities of wood within the core affects the swing weight. Bear in mind that some wood can be damaged by the force of the press. The choice of species become important, once you start thinking about bond strength, wood to wood and wood to epoxy.

Search 'mechanical properties of wood', should take you towards www.fpl.fs.fed.us

I agree with your philosophies and what others have said here. To join the binding area to the front and tail of the ski use a finger joint or what I do is mortise/tenon the joint. I make the binding area which is hardwood (maple, ash, etc) have the tenon, the softer wood has the mortise (tenon slides into the mortise). I would stay away from butt joints when joining the binding area to the rest of the wood core. It's "probably" ok since most of us butt joint tip spacers.... but just seems wrong for the binding area, why chance it.

I've been using douglas fir for my softwood. Poplar is a semi-hard wood and many ski manufactures use it for the entire wood core.