Ski Builders Forum

Ski dims: 137-105-122 188cm
Core size 168cm
55% ash/45% poplar core with a long taper to a 35cm swollen semi flat spot underfoot.
2-11-2
12oz biax and 4.1 oz carbon 0 degree uni stuff from sollar composites top and bottom.
Wood Veneer topsheet, zebrawood
Super Sap epoxy.

I realize a stiffness profile is massively dependent on the core but am I gonna be way under composite weight just making these noodles or what?

In my experience the wood topsheet adds stiffness on the 0 degree.
The ash is stiffer than the other core blends I have made. The core feels great, stiffer in the tail for sure but not too soft up front.

Am I trying to get to a full weight of composite close to a 22oz that I have used in the past?
OR use 1/3 of the remaining weight after the glass as a carbon composite?

Would a 9oz carbon be more appropriate here?

Ski is also somewhat skinnier than others I have made.
We made a few like this but plastic topsheet and full triax and polar/maple and poplar/beech cores that were also thicker than the above dims but profiled on center.

ahh so many variables.

Your thoughts?

MM - I'm not in a position to critique, but can I ask a couple of questions?

The bearing surface is around 1900 cmsq'd per ski - what size of the rider do you have in mind and what sort of conditions - is this all mountain dimensions for your neck of the woods?

12 oz biax - is the weight distribution 50/50? If so, is the carbon a little vulnerable if laid 0 degrees. Perhaps you could rotate the biax to +/- 45 degrees and add uni in 0 degrees. I think this the second option laid out above?

If Matlab weren't so tight with their trials, we could run a few numbers ...

This is for me 185lbs with gear.
In bounds mostly for some bumps and some dust on crust application, with new snow up high and packed down below. Snow is soft here, more so than most places.
The 12 oz is a +/-45 and the carbon is uni on the 0 axis.

So, I got the CF was uni, but I'm thinking it is a little vulnerable and needs supporting with fibreglass (0 degrees). You don't need to use the whole 9 oz, but if you don't add something, 2-11-2 will verge on noodle territory IMHO

Yeah. How do i find a light weight uni glass? Need like a 5oz ? Perhaps. A small diamond of triax? Or a 9oz diamond of uni glass?

What's the general consensus with carbon. twice as stiff as fibreglass?
If so 4.5 oz carbon uni would be like 9oz uni fibreglass taking your total up to 12 + 9 = 21 triax.

You could do biax glass, uni carbon, core, uni carbon, biax then another layer uni carbon?

falls wrote:What's the general consensus with carbon. twice as stiff as fibreglass?
If so 4.5 oz carbon uni would be like 9oz uni fibreglass taking your total up to 12 + 9 = 21 triax.

You could do biax glass, uni carbon, core, uni carbon, biax then another layer uni carbon?

i thought so.

Brilliant but I A) i don't have enough carbon and B) I am unsure about uneven composite layers affecting the cure results.

I think I will get some 9oz uni glass and only use like a 4" wide piece top and bottom to back up the carbon maybe.
from here
http://thayercraft.net/Style%207721.htm
or here
http://www.cstsales.com/uni_s_glass.html
ooo carbon too...
http://www.cstsales.com/uni_carbon_fabric.html

Moment and ON3P use carbon asymmetrically. Moment below the core and ON3P above. I think it probably affects the layup when heating, but I think it is predictable/repeatable. I think below the core increases camber and above the core reduces camber (?), but you can probably build this into your moulds. I think either SHIF or Dr Delam actually have flat moulds and use uneven heat to create camber.
Likely though you already have the mould and want the ski to match it.
I would also say if your ski is narrower than the usual you will need more composite for the same core profile. It's hard to say how much though.
Have you run out of triax?

I was thinking the CF might be vulnerable towards the tip area (protect against excess load) and this is the area that might feel a little too soft. Aramid tape below (pull in the dampening effect of this fibre) is an option or the light weight uni FG (top and bottom) in the second link?

You could leave the ski naked, which would allow you to add another layer if you are unhappy with the feel or camber - might help you deal with any surprises when using the super snap.

reading your topic i remembered that i did some calculation on the "glass vs carbon" thing. it s not representive, as there are too many kinds of different glass and carbon fibres out there.
but for some basic knowledge i think it could be useful.
its still german, if no one else does it till then, i ll translate it tomorrow, im in a hurry right now...
https://lh4.googleusercontent.com/-4EPr ... KvsCFK.jpg

falls wrote:...I think either SHIF or Dr Delam actually have flat moulds and use uneven heat to create camber....

No sir, my press forms all have a little positive camber. I use a balanced composite schedule, equal materials below and above the core. Always having strips of unidirectional carbon fiber to bolster the triax glass.

I only heat from the bottom and do a slow ramp up to elevated temperature. Then a long soak at temp followed by a very long ramp, under pressure, back to ambient, basically overnight. Certainly not production worthy technique, but good enough for an avid hobbiest such as myself. My skis retain the exact same profile as my press forms which makes designing skis easy, what you see is what you get.

-S

Hey shif, I have read some of your layups and they are complicated, I may be on that trail.
Any suggestions on this one? No Bueno?

I may press naked and then if I need to add a heavier uni glass on top I will with the topsheet, now that I double press and heat on both sides, oh yeah!.

I Will drop some biax and chopped in the binding area and some small diamonds of triax in the tip/tail transition area to bolster that and prevent a break.
Hell, DPS doesn't have any glass but prolly a heavier uni weight and their skis don't break, just delam and rip out bindings, prolly cause the core is like 6mm thick and bamboo.

MM, Once upon a time I planned to use biaxial glass with uni carbon just like you propose. I bought some of the biaxial FG from Raka and found it difficult to work with so I never tried it in a ski. I cut my materials into six inch wide strips and the biax fabric was almost falling apart, very hard to make it behave.

I like the idea of uni-carbon fiber in the diagonal bias orientation with uni glass lengthwise, the ski would be torsionally stiff as hell. Soller offers braided carbon biaxial tape, but it’s rather heavy and costs a fortune. I’ve not found other sources. It is conceivable to use multiple pieces of 12 inch wide uni-carbon fabric cut at a 45 degree angle, assuming your epoxy has a long working pot life because this is an intense lay-up.

I would definitely use the heavier uni-carbon with your core profile. Methinks an 11mm core would yield a very flexible ski. I’ve used cores everywhere from 10.7mm to 14.1mm thick and the results are dramatic. I’ve settled on about 12mm for soft skis and about 13mm for stiff skis. I’ve also found that doubling the uni-carbon weight stiffens the ski on par with a 1mm increase in core thickness, or thereabouts. These numbers are adjusted for my weight, about 230lb with gear, and I prefer relatively stiff skis.

I like the dimensions of your ski design. I’ve build several pairs having 137-102-123 @ 185cm dims and they are very good all mountain boards.

I’ve never needed to reinforce the binding mounting zone with additional composite pieces. I mount my own bindings using the appropriate drill bit diameter, then use Titebond type 3 glue to set the screws. So far we have never had a binding pull out, but you may be doing some crazy ski maneuvers and need the extra strength. My bamboo cores run tip to tail with about 16mm of tip filler wrapping each end. I don’t add layers to reinforce the transitions, not required.

Like you say, so many variables…

-S