Ski Builders Forum

Hi all,

I am now working on BM skis. The core will be made out of siberian cedar (wanna save some weight). It holds screws much better than poplar for example, but it is still soft wood. Because the dimensions of my skis are 195 R 45 (136 - 116 - 124) and because the flex should be as stiff as possible I don t want to risk ripping out the binding.

The layout:

base with edges
rubber
600 g biaxial glass
300 g biaxial carbon
unaxial carbon stringer 330 g/5 cm bride
cedar woodcore
unaxial carbon stringer 330 g/5 cm bride
300 g biaxial carbon
600 g biaxial glass
oak veneer topsheet (0.8 mm)

My ideas for binding reinforcement:

1) prepare thinner core and use thicker ash veneer topsheet 1.4 mm

2) add 800 g fiberglass just under the binding

3) use hard wood plate inserts in the binding area (as shown on the picture below the text)

The hard wood inserts seems to be quite challenging, I am not sure about gluing it into cedar core. I could do it with classical woodglue before the layup or with epoxy while laying up.... Both have some advantages and disadvantages. Not sure if that sollution is worth to try..... :)

Thank for any advices!

Those things will be way to stiff with all that composite

It is going to be stiff, but it should be stiff

anyway the glass and carbon is biaxial +- 45° for concreet torsional stiffness. unidirectianal carbon tape is for overall stiffness. I built couple of pairs with some combinations of theese materials and I think I now which stiffness I can get after this layup.... I want it stiff

but for imaginaition - the same setup, just without unidirectional carbon tape stringers is softer then the same setup with two unidirectional stringers without +-45° carbonfiber..... But both theese setups are not as stiff as I want....

1) wont work I think.

2) seems sensible to me, also easy to do.

4) You could also think about Inserts if you have a perfect layup way - if core shifts just a little little bit, inserts are crap.

I suppose my layup quite exact, I use screws in the tips and tails, my bases are longer than necessary (I do not use edges around tips and tails), so inserts could work but what if I want to change center point or binding.... No inserts are for snowboards :)
I was thinking about routering 1.5 mm deep trough (6 x 60 cm) in the binding area and I would add piece of that fiberglass and ash veneer over it to fill the trough. That could be easy to do :) that is sollution number 5.... Just choose the best.....

I've used the hardwood insert under the binding method and ended up with really stiff skis.
On all my skis I use aluminum window screen under the top layer of fiberglass. This has held up great. Sometimes I use just enough under the binding pieces and other times I use the screen material on a longer segment of the ski.

That amount of glass also adds up to a lot of resin and also therefore a lot of weight. These skis are going to be heavy.

Thanks all for advices... I made a little test with wood glue. I made little ash plywood (2 pieces of 1.4 mm ash veneer glued together and then glued on piece of cedar) it is impossible to brake out of to single pieces and it holds screws until it cracks...

so i wil reinforce the core with this way under the binding.

i don t think that theese skis will be such heavy... I ve built skis in dimensions 191 (140-108-124), middle stiff, concrete torsional stiffness and the weight of one ski is cca 2350 g or less. Core is out of ash/siberian cedar (50/50 cca). Composites are two layers of 600g glass and two layers of 300g carbon... That mean the same setup like for my Bm skis only without carbon stringer tape, which increase the weight of one ski about of 150 grams or less...

so with full cedar core (2.5-11.5-3), a little bit of ash underfoot and some carbon stringers i can count with maximally 2.5-2.6 kg per one ski. And this is i think quite ok for stiff Bm skis in such a dimensions....

1) whatever works, works!

2) try it, what have you got to lose? !!

3) report back, good luck!

If life is not at stake, there is nothing to lose :) ......

I will post progress with these big boys, maybe there is someone who is interested in similiar type of skis like me :D

There is a final drawing of them:



today I was working on bottom mold, tomorrow I have to finish it and start with cores.... This must be everything well done, I plan to try them even in some freeride competiton....

Well, just almost finished my cores... It is made out of siberian cedar, black locust sidewalls and "little ash plywood reinforcement" under the binding

I am pretty happy with the core flex - so stiff and light in the same time... (2.6 mm - 12.3 mm - 3.2 mm). There is no need for carbon stringers. I will probably use only torsional reinforcement - biaxial +- 45°, maybe just fiberglass 600 g (or I will add 300 g of carbon biaxial)

Here are some pictures of the core, and the binding reinforcement:





















still not sure if to use woodglue or epoxy to attache the ash plywood reinforcement. I made little test and the wood glue holds better then the wood itself. The wood always broke earlier than bond... So it would be maybe easier to use woodglue. There is also no moisture inside of core, because it is all covered with many other layers....

Epoxy, it will fill any gaps. A negative mdf template and a guided router bit will help you improve the finish the next time you do this.

A layer of fibreglass between the two parts would increase the pull out resistance. Sharpen the drill bit before drilling the holes for the binding screws, this will give you the best results.

I agree some glass inside the channel under your binding plate would work well. Probably only need some biax ion there.

pavelbozak,
great looking cores!!
I made a very similar pair last year and the similarity of the side cut to the reverse camber will allow the stiff ski to turn easily.
12mm might be a little thick for that wide of a ski.
For sure you'll be able to go really fast!!

jono:

thanks, that was my idea. To put little reverse camber to improve handling even in smaller speed... How much have you overrockered your rocker shape bottom mold to get nice small rocker underfoot? I am not sure how much it will decrease. But i suppose it will be very similiar to camber deceease. ( i use 12 mm high camber mold to get cca 7 mm of camber)

vinman, Richuk:

yes, i was thinking about epoxy with fiberglass too. And i would made template for that after, if that worked well :) for that attempt i am quite fine with unsmoothness of the routered area. In fact it is not so bad. But i should press my skis after this reinforcement is already attached and brushed... ? In layup i am not sure for doing that...[/quote]