Ski Builders Forum

i remember having seen once a pic of kam "touring" with his skis. sadly i can`t find it anymore... on this pic there was hardly any snow visible, it was more of a rocky field so i somehow understand that skis only last 10days.

but it would be interesting to see where/how/why the ski exactely delaminate. is it delamination between the fibreglass layers or is it between the fibreglass and the woodcore? i suppose it`s the second - and now it get`s really interesting: is it really delamination or some sort of ?fatigue?... i mean fatigue maybe of the bond between glass and wood, or fatigue of the woodcore. like if a tiny layer of the upper part of the cores would still stick to the delaminated fibreglass, some sort of "ripped apart core".

every once in a while i do some tests with cutaway leftovers of skis and skateboards. i try to rip away the fibreglass and stuff like that. and in most cases after i ripped away the glass you can see some little woodfibres sticking all over the fibreglass. it`s covered with them!
for me this implicates following: the bond isn`t the weakest layer in such a construction. during lamination the uppermost parst of the wood get soaked by epoxy. they stick to it. after curing when you rip those layers apart these fibres still stick to the fibreglass because the epoxy creates a very strong bond. so when you rip a sandwich construction apart you rip the wood apart because the internal bond between the wood fibres is weaker than the bond of epoxy/fibreglass/wood.

a bit like on the foamskis: viewtopic.php?t=543
there you also can see that the foam still sticks to the fibreglass. same thing with wood but just less extreme.


if it would really be as i described, then the type of wood does have a significant influence on how long a ski lasts.

As for the 10 day number... that is about average for me as well. Except that I usually try to do some sort of repair if they start to delam. Then, I just keep skiing the ski until it totally blows up.

Keep in mind too though that if you are pumping out 1 pair of skis a month, and want to be skiing them, and have a job that doesn't involve skiing, it is pretty hard to put more than 10 days on a pair of skis before you have another pair to test out. And, eventually, when you have 10 or 20 pairs of skis, you will always be trying different skis for different conditions, so no individual pair gets that much use.

I was hoping to build my ski's with dynastar style toughness. Otherwise this already expensive hobby will become even more expensive

well, i have 13 and 17 days of partially hard ripping on my homebuilts... and there is still absolutely no sign of delam... but consider what i tried to explain - is it the wood that gets ripped apart?

The "10 day" delam seems a little low. It really depends on how and what you ski and also how you made that particular pair. My second pair of skis that I made lasted me all season at Squaw (130+ days). Sure the top layer was scratched to hell (no topsheet) and the sidewalls were chipped (tried the epoxy method) but there was no delam and they're definitely rideable right now. So don't let this supposed 10 day thing deter you from building.

130+ days!!! Wow I wish I could shred that much.

yeah me too ... not any more though. I only got to ski 10 days or so last year.

I was kind of wondering about this. We put over 40 days on the Doods and 25+ on the Big Labowskis and other than some scratches and a couple of top sheet chips they're running strong.

I hope I can get 130 day on mine That would be ~3 seasons... if we see any snow

Hafte

hey guys. sorry for the delayed reply. work has been crazy.

well, i skied my new skis last week and this past weekend. they delammed after one day. in fact, they delammed before i even skied them, after a few flex tests, but skiing on them didn't make matters better. okay, so how do i define delam? well, for me it's any sign of separation between the materials, mostly due to intentional 'hard' flexing and use. i don't really count 'chipping' as a delam so much, but it depends on how the chip was created, etc. although chipping can be something that creates a weak spot which causes delam. anyway, i'm very picky about my skis and how well the materials bond, so any slight hint of material separation is pretty much considered a delam to me. some of my skis have a little delam but they don't get worse. for example, i've put in about 25+ days on the Bangers and they seem fine.

but most of the delamming i've experienced is between the edge and the rubber/glass layer. the delams mostly occur at the tips and tails, often around points of high stress, like the ends where the skis get banged up or around the curvature where there's 'stored' energy like a compressed spring. the delam may not be readily noticeable, but it's there. my latest skis have Ptex sidewalls and the delam is between the glass layer and the sidewall material. everything else is fine. i know what caused it and it's poor preparation of the sidewall material. after i flashed the skis, i flexed them and heard the familiar sounds of materials 'shearing' apart. i looked more closely at the sidewalls and noticed the separation. i haven't noticed the separation as much with wood sidewalls because the wood bonds well. i've been trying a number of techniques to improve the boding of certain materials, especially ptex. some of my skis survive about 10 days of ski touring before i notice the first sign of delam, but again, the delam may be small and it may not propagate. still delam though.

someone asked about whether i've broken commerical skis before. well, i'm not an abusive skier or any harder than the average skier. but i have broken about a handful of skis. one pair i broke on the first day after making the second turn! they were a pair of RD Valdez Extreme downhill boards (212 cm length). granted i was going a bit fast and out of control, so on the second turn the front end of my right ski folded into a 90 degree angle and threw me like a rag doll. luckily i was not harmed. i immediately took the skis back to the dealer and they were surprised to see it broken and were happy to give me a new pair. i just bought them the day before and they were on sale. i've bent a few other pairs in a similar manner (PREs and Rossi skis), and i've experienced delams in the Volant skis as well as a couple pairs of K2s. so normal skis also delam and break.

most of my skiing is touring and the snow conditions can be interesting, but i don't think it's too much harder than say park riding. here's a photo of me skiing on my new skis last weekend taken by a friend. i skied pretty much until the snow turned to grass and dirt (about another 300 vertical feet). i only managed a few stratches on the base material but they were quickly fixed on Kelvin's wet-belt sander.



i'm going to take some photos soon of the delams on my skis so we can continue this discussion and maybe compare with other home-built skis.

Little Kam's Ahmo's which experienced 130+ days held up well, so it would be interesting the see the photos.

BTW: plywood, is this the picture you were looking for?