:: View topic - can you epoxy the tip spacers to the wood?

can you epoxy the tip spacers to the wood before you put it into the mold so it holds it togeather throught the whole process?

I skied my newest pair of skis the last two days (I will do a full writeup soon), and while they skied great, one of them had a serious topsheet delamination. I think it may have been because I didn't get enough epoxy on it. The fiberglass held together great, and the core is still bent as it is supposed to be. I plan on pulling the whole topsheet off in a couple weeks and relaminating it back on. But I was just wondering if any of you have had similar experiences.

As a side note, I used 4 layers of fiberglass to create the tipspacers, and I am really impressed at how tough they are. Additionally, they didn't relax at all when I pulled them out of the press, so the tips are huge looking.

Did you have graphics on your skis? or any color printed on? this can often cause delam if something isnt right in the ink mix.

Otherwise the most common problem is dirty topsheet, greasy substance can cause heaps of trouble, or possibly not enough pressure on part of the ski while pressing.

what kind of topsheet material are you using? was it abraded?

we've had some delam issues, mainly due to poor bonding with ABS tipspacers. the abraded p-tex works well.

can't wait to see the photos.

kam

I used base material for the topsheet. The more I have been thinking about this, the more I seem to remember not putting a lot of epoxy on the top layer between the topsheet and the top layer of fiberglass because when I mixed up the epoxy, I forgot to plan for the 4 layers of fiberglass I would have to epoxy at the tip. I think this must have been the problem and as soon as I get a chance, I am going to pull off the bindings and re-epoxy the topsheet down.

On the first ski of this pair I didn't get the epoxy fully mixed because it was the first time I had used the epoxy. The epoxy in the bottom of my mixing container didn't get a full ratio of hardener. The topsheet being the last piece to get epoxy got all of the unmixed epoxy. When the ski cured, the topsheet never cured on and the while the rest of the ski was solid, the topsheet peeled right off and was still sticky. I re-epoxied the topsheet on, and it is holding on quite well now.

Greg - did you think about using some filling material. There is a stuff called cotton fluffs (or flakes - don't no how to translate it correctly). Mixing it with epoxy creates a great (stronger an lighter) glue that is able to fill the gaps.

Very interesting design ideas:

http://www.dpskis.com/

very interesting prices too...

what the hell is that! has db split?

haha! prices are getting ridiculous!

Heck, for that price, you might as well just build your own!

or build nine pairs.

For the story about DB -> DP look here: http://www.telemarktalk.com/phpBB/viewtopic.php?t=10064&postdays=0&postorder=asc&start=0

Well, I wonder why the price is not going down. They are now making classical wood core - carbon skis, rather then AirexC70 - carbon. And apparently they moved the production from US to China. You can get few hundreds pair of high quality skis at 80$ each (shipping included).

But as long as people is happy to pay a lot...

About the Lotus 130, I like the fact that the widest part is about 40/60cm from the tip.

Yes - prices are just crazy - but people seem to pay it. Here in Munich there are some dealers selling ski for more than 800,-EUR and they have much more than one pair in stock!!!!

But that wasn't the thing i wanted to make you know. I've been watching the company (former db) for some time and what's realy interesting for me is the transition in shape and construction:

Last season they were absolutely convinced that traditonal sidecut still is optimal for powder skiing. This season it goes towards water ski like design - the way Shane McConkey went with his Spatula - but they try to improve things for harder conditions by combining a tranditional center with reverse sidecut tip and tail! Is this the way to go? Something that should be tried!!!!

The new construction with the wood core confuses me a bit. The former design with a carbon fiber structure (the foam just giving the shape) adapted from aviation design principles was just awesome. I spent some time thinking about using it myself for my own ski - too complex for the first try - but i want to return to it some time.

This might be the reason why they gave it up - just to complex for a comercial ski.

I talked to CB about it 2 yrs ago and he told me they had tryed woodcores but could not avoid delamination with them. that's the reason for the vertical stringers in the foam. CF skis with wooden cores was what they were aiming for all the time. Will be exiting to see if the cinese managed, (and not Goode)

Hmm - that's interesting - the only reason i see for moving back too wood is the dampening (absorbing vibrations). Do you know more details?

Delamination? Was this because of the enormous difference in stiffness between wood and carbon just making it pop off? The bonding with the epoxy should be absolutely the same!?

I suppose that it should be like this: the foam is quite stiff in compression, but it has poor mechanical properties in tension (I bought some Airex C70.75 to make a carbon seat for a paraglider). When the ski is bent, in the tip and tail the top and bottom carbon layer tend to squeeze together, so the foam can sustain the stress, but in the biding area the two layers tend to pull apart, and the foam just breaks. The vertical carbon walls help to keep together the top and bottom layer.

I think it can be tricky in a factory to optimise this construction for mass production. But if you build ski in the house, it is not such a big problem. Airex C70 is easier to machine than wood, I think.

Probably, in the case of wood core, the situation is like the one proposed by Alex. I should try to do some simulations (FEM).

They said they add some kevlar to add dampering

Bending a ski means tension on the lower laminate (maximum close to the base) and pressure on the top layer. These forces will shift both layers against each other. To compensate the forces you need a connection between both layers taking the shearing forces. This can be implemented by a complete core or by just joining both sides with a small but strong "wall" (think of an airplane wing construction). If you use carbon fiber for this it almost prevents the shift - foam or wood is not that stiff so it will allow a certain amount of movement. Consequently you gain a lot of stiffness with minmal weight.

What davide mentions is the buckling of the shell due to the pressure in the laminate. This can be well compensated by a foam. Airex or Rohacell are ideal for this.

Well, in the central part, where the bindings are mounted, the top layer is rigid, while the bottom one tends to bend, I think, and try to delamintate from the core, but it should check it.

Thats an interesting point Davide. My consideration simplified the ski to a structure were forces will affect from the center (like the mentioned wing of an airplane). The center part of a ski is almost rigid and forces from the binding will directly go into the top layer.

You mentioned doing some simulations with FEM? This would be a very interesting thing that may lead us to engineering a much better mechanical structure!

haha you could get started on making skis for about that much