Alder cores anyone?

[dbtahoe]

Has anyone ever used Alder. It's used alot up here at Lake Tahoe. I have a friend who owns a cabinet shop and has a lot of drop of clear lying around which would be nice to not see go to the dump or up a chimney.

Here's some data for your consumption
http://www.cloudberryfurniture.com/english/alder.html

Thanks for you insight.
Doug

[G-man]

Hey dbtahoe,

You might remember from some of my posts in the past that I basically think that using one wood species over another for a ski core just doesn't make that much difference in the performance of a ski... a little variation in dampness, maybe, or a bit of a difference in binding screw retention, maybe. Much more than that is mostly ski industry hype, in my sometimes not so humble opinion. Remember bigKams 'project pallet' skis.

Anyway, Alder is wonderful wood to work with and it's real pretty. I'd say grab what you can from your friends shop and build some skis... maybe skip the top sheet and just put polyurethane on 'em. I bet they'd be real beauties.

G-man

[Greg]

I'll second that about any old wood working. That is the best part about building skis.

After having spent too much money on a couple of my cores, I learned that the best cores are built from wood that is Free. Plus, with free wood, you get a chance to be a little more creative in how you set up the wood, finish it, etc.

That said, if you got some clear alder. Go for it. The worst that will happen is that the skis break when you hit a stump or rock too hard. And we all know that the "best" factory manufactured skis break on occasion too.

[plywood]

from what i just looked up i can tell you that alder should work fine for skis.

they say that it is a light, soft but tough and good bendable wood. sounds ideal for making skis and if you got it for free then go fot it!

i`d like to discuss more about wood! i just bought some ash and yesterday i got some very cheap fir. the differences between those two woods are vast! it starts with the price: fir cost me about 1/5of the price of ash. the bending-abilities are really interesting. it feels like with ash you don`t have to care if the rips of the annual rings are vertical or horizontal (grains of course lenghtwise). it has the same strenght and bending properties in both directions. but with fir it seems to be a bit different. i tried to breake some strips. if the rips are in a vertical position it took me a bit more effort than when i flipped the lath lenghtwise for 90°. then the ribs were horizontal and the wood did crack along those ribs. i hope you understand what i`m trying to explain.
and ash needed a quite bigger load until it collapsed. then it didn`t instantly crack and breake apart. it started with some grains splittering away until a certain point and then you had to twist the rest of the wood even more. it didn`t break apart, it just got some damage, but the piece staied together...

i`m really looking forward to get a ski done out of my fir. it is extremely light, maybe half the weight of ash... but i think such skis are going to collapse on the first bigger impact. on the other hand: K2 uses fir for their factory skis...

[G-man]

Hey plywood,

One thing that a lot of folks don't realize about wood characteristics is that different samples of a particular species of can vary pretty drastically within the species. Over the last 20 years, I've milled around 300,000 board feet of lumber from diseased trees, mostly Ponderosa Pine, Douglas Fir, Red Cedar, and Black Oak. One thing that has always seemed consistent is that even if two trees of the same species are growing relatively close to one another, the lumber from those two trees can turn out quite different. Some of my pine is quite soft and some of it is as dense and heavy as oak. Some pine test strips will bend into a complete circle without breaking, and some of them will break quite easily. Even different samples of wood from the same tree (or from different edges of the same board) can vary significantly.

So, the fir that you get in Europe may be quite different from the fir that I cut in my back yard or that I could get at my local Home Depot store. These variations make it rather difficult for us ski builders to have a very objective discussion about the qualities of different species of woods.

Regarding your fears about your fir core skis collapsing when you work 'em a bit, remember that for many years different ski manufacturers touted, and built, foam core skis. They actually held up quite well, so your fir skis should do just fine. As a demo to skiing partners while we are gearing up at the trail head, I have launched a pine core ski into the air as far as I can toss it and let it come crashing down onto the asphalt pavement, usually bouncing a time or two. Then I pick the ski up and toss it like a spear down the road. I've often suggested to my horrified friends that we do the same with their factory built skis. They have always declined to participate. My skis have been subjected to this abusive display about 30 times and have only sustained a few minor scratches.

Regarding K2's use of fir, consider the following. The wood core material is about the most expensive part of a ski. Consider further that well over 50% of the original material gets turned into saw dust. Wood is relatively heavy, so transportation cost of the raw material is a big consideration in the overall cost of manufacturing a ski. I doubt that K2 skis that are now made in China are being made with Pacific northwest fir. But when K2 first started making skis, they were located in the Pacific northwest where fir was the most abundant and available wood. Companies who made skis in Colorado made them from Aspen, the most abundant wood in that location. The same goes for New England ski makers who used Maple. I'd be willing to bet that the K2 skis that are being made in China are using a core material that is most cheaply available to the factory on China.

Again, I say that the type of wood that you use in the core doesn't matter much at all in the performance of the ski. Light, soft, and damp is my focus. I use the actual structural components (composite fibers and resin) to give the ski performance. I use inserts to keep the bindings attached because the soft woods don't hold screws very well.

Regards,

G-man

[hydrant71]

very well said g-man, i completely agree.

most production cores
are built from finger jointed boards. many sections of wood finger
jointed together because it allows them to use the absolute cheapest
grade of that species of wood. cut out the defects, finger joint and glue back together. poplar is used now because it is cheap and it grows
really fast, and it is available almost everywhere. when i have messed with it in my shop it seems really soft and elastic, makes a weird fuzz
when you machine it. not what i would think would be stellar as a core,
but it is used in many many of low to mid line snowboards, and it works really well. foam was used extensively in snowboards in the 80's and 90's
before the "it has to be wood or its no good" craze started, after which nobody could sell foam boards anymore.

basically if foam, finger joints, and wood grown to make toilet paper works
alder should make some really fine skis.

jason

[plywood]

you bring up good points!

so would you say that for a "normal" style of riding it doesn`t matter that much what kind of wood you`re using?
and with normal style i mean no big jumps and stuff like that which would bend and stress a ski more than during normal riding...

what do you think? i suppose that this could be how it works...and that a ski with say ash core would withstand a harder impact better than a core with poplar or something similar... or do you disagree? because i really can`t imagine that such cores can take much stress from what i tried with several strips...
or is it like this: the tinner the stripes, the more they can be bent?
do you think manufacurers use such "weak" woods also in tip and tail, or do they stop the woodcore before tip and tail begins and take there some sort of rubber/ptex or something like this as "core"?

[rockaukum]

Please help me understand this... Alot of talk about the wood core types... There have been many mfrgs that have used Foam cores (Including my atomics that will be soon for sale) and have had no problems (that I'm aware of). The structure of the ski is based on what is wrapped around them... either Glass, carbon, or whatever you choose. These properties will enhance or take away from the ski flex and torsional rigidity. Am I missing something or just use wood for a filler and if screw retention is of concern use inserts or a metal plate in the binding area?
Give me insight because I'm ready to ski my skis made from ripped 2x4 DF including knots at no extra charge.
rockaukum
P.S. remember that it will be FUN to ski the ski YOU made!

[G-man]

Hey rockaukum,

Yep, I think you've got it. The only thing that I'd add to your statement is that the choice of core material also influences the damping qualities of the overall ski assembly. I'm partial to a medium density wood.

Basically, the core material functions as the medium for maintaining a fixed distance between the structural layers (top and bottom composite layers) of the ski. The further apart these layers are in relationship to one another, the stiffer the overall structure becomes. As long as the core material has the compressive strength to resist the forces that would otherwise allow the structural layers to move towards one another when stressed, that material could theoretically be used for a ski core. Of course, we want to use the lightest possible materials in the construction of a ski, so that reduces the number of possibilities.

to plywood,

I think that core failure is one of the lesser concerns when it comes to building a really durable ski. Probably the biggest issue in ski failure is (first) a deficiency in the bonding of the different components of the ski, and (second) deficiencies in the composite structural design... as in not enough fiber or fiber not used most effectively. Occasionally, a ski that sees a lot of hard use, such as big jumps and hard landings, suffers a snapped tip or tail. I think pretty much all of those failures that I have seen have been related to a poor structural transition of the design elements in the tip and tail that has lead to stress risers and weaknesses that eventually lead to failure. The famous K2 factory video from a couple of years ago was a good example of how not to design a tip structure. Virtually all of the components of the ski transitioned laterally at the same basic location in the tip curve. Yes, there was a little bit of staggering of materials (by a centimeter or two), but a really good design would focused on a material transition that was as smooth as possible, limiting weak transition areas. Skis that break in half, should not break in half because of the choice of wood used in the core. If they break because the wood core failed, then the overall ski was not properly designed in the first place.

Basically, if your ski's chemical and physical bonds are adequate, if your composite layers are designed and laid up properly, and your material transitions are without stressors or weak points, I'd say base your core material choice on damping qualities and how you're going to attach your bindings... oh, and on how pretty your wood grain looks if you're gong with a clear top sheet.

Okay, I gotta shut up for awhile. Maybe I shouldn't have taken the Summer off from Skibuilders... now I can't shut my yapper.

G-man

[plywood]

i wouldn`t second that!

i`ve made pretty different experiecnes so far.

there is a skateboardcompany in switzerland which uses vertical laminated woodcores. the shape of their boards is pretty narrow. and their boards are very lickely to crack. i`ve seen a few broken boards, and on all of them it seemed like the crack had started in the middle of the wood. it sounds pretty weird... but i think there is a connection between the likelyness to crack and the tickness of the core.
mabe it goes something like this: the thicker the core, the more load the wood has to take. the outmost parts of the core have to take up a bigger load on a thicker core. this could create some shearforces - and these forces could get just too much for the wood and may rip it apart.
because the outmost part of the wood is bonded to the fibreglass it would look like the crack started in the "middle" of the wood...

what do you think about this? am i wrong?

of course i`m aware that there are differences between skateboards and skis: said skateboards were maybe 8-10cm wide in the area they broke. and they have to take the full load of a person with a core thickness of about 6mm - bigger load on weaker board.

[G-man]

Hi plywood,

what do you think about this? am i wrong?

I'm just an empirical tinkerer myself (not formally educated in constructing stuff), which hardly qualifies me to be one to judge the accuracy of someone else's ideas. I mostly spew out thoughts and ideas, then wait for someone who is actually educated in the field to provide more reasonable information, which, thankfully, the World Wide Web seems to be loaded with folks who are eager to share information. But, as you've probably noticed, I do like to yak about building stuff .

Regarding your comments in the above post, I think that you may be on to something. It seems that the structure of a ski, under stress, would behave much like a beam truss, with the top and bottom composite layers of the ski acting much the same as the top and bottom chord members of the truss. As the composite layers are subjected to tension and compression forces (via flexing of the ski), those loads are transfered to the fibers of the composite and to fibers of the wood core of the ski as shearing forces. The epoxy bonds that hold these two mediums together act as the rivets of the truss.

I agree that as the core gets thicker, it requires a greater force to achieve a given amount of flex in the ski. However, one of the main reasons that we employ a thicker core is that we are trying to reduce the flex that a given force (our relatively fixed body weight) will cause in the ski. So, I don't think that the shear forces increase just because we increase the core thickness, unless we somehow at the same time increase the forces acting upon the ski, i.e., by skiing more aggressively, skiing on steeper or more firm terrain, or by carrying more weight. You may well be correct in your view that with certain very aggressive skiing styles, the resulting forces may exceed the capacity of certain wood fibers to resist the shearing load.

the outmost parts of the core have to take up a bigger load on a thicker core.

I'm just not sure if this would be the case, or if the load would be uniformly distributed throughout the fibers of the core. It does seem, though, that as forces increase, the epoxy bonds at the composite/wood matrix (the rivets in our truss) are the weak link in that their load bearing capacity is relatively fixed. Here, we just have to follow the basic rules for good bonding... abrasion, surface treatment, chemical cleaning, and proper use of the adhesive. As we've seen a number of times, some builders actually use real rivets to increase the bond strengths of the layers of the ski.

Oh, ya... I know a bunch about the difference between skis and skateboards cause I spent much of my adolescent years on either a skate board or a surf board... but that was back in the 60's... early 60's .

G-man