fiberglass and carbon proportions O_O!

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bhenry
Posts: 61
Joined: Thu Mar 01, 2012 8:49 pm
Location: Indianola, WA

Post by bhenry »

Resurrecting this thread once again. I’ve been away from building for a couple years but ready to have another go around.
I’ve searched many threads looking for info on carbon/fg combinations. One thing I’ve learned is there is no single answer... I talked with a guy at fiberglass supply and he recommended trying 12oz bias fg and 4.4oz and 6.7 oz carbon uni.
My current design is a core of red cedar, bamboo stringers in binding area and ipe side walls. 2.2 11.5 2.2. The shape is 140 112 120 semi pintail with early rise tip. I’ve built a number of these and am looking for a light touring ski. Thought I’d try -

top sheet
6.7 carbon uni
12oz fg biax 45/45
Core
12oz biax
6.7 carbon
Base

I’m curious what the results were in similar lay ups in this thread and if I’m way off base. Carbon’s not cheap

SleepingAwake
Posts: 171
Joined: Mon Oct 11, 2010 11:06 pm
Contact:

Post by SleepingAwake »

I made some quick calculations based on your info and compared it to my go to flex profile. The numbers are not overly precise but should be close enough (unless you planed to use high modulus carbon...)

The tip is 16% stiffer than mine, the center is 60% stiffer than mine and your tail is 15% less stiff (...insert joke here).

On top of that 6.7oz uni carbon really is on the light side. And I think skis with uni carbon (mostly) suck.

My proposition would be to go with something like that:

uni glass
biax carbon
core
biax carbon
uni glass

The main weight saving in a carbon ski comes from the thinner core, not the lighter laminate. It's actually really rather hard to design a carbon ski as carbon is just really stiff so the core needs to be really thin to get some flex, which means you need a lot of carbon otherwise it's going to break which means you need a thinner core and so forth. I would recomend sticking to uni glass unless you know what you are doing. Which means you design the core profile based on your layup, and not the other way round...

I hope that helps for starters...

bhenry
Posts: 61
Joined: Thu Mar 01, 2012 8:49 pm
Location: Indianola, WA

Post by bhenry »

Thanks for the reply SA. Well, I already have the carbon and glass so I’ll take another look at this. I have 20 and 22 oz triax as well so I can mix and match and come up with something

Just curious what you were comparing to my layup to?

Cheers, Bill

bhenry
Posts: 61
Joined: Thu Mar 01, 2012 8:49 pm
Location: Indianola, WA

Post by bhenry »

Thanks for the reply SA. Well, I already have the carbon and glass so I’ll take another look at this. I have 20 and 22 oz triax as well so I can mix and match and come up with something

Just curious what you were comparing to my layup to?

Cheers, Bill

SleepingAwake
Posts: 171
Joined: Mon Oct 11, 2010 11:06 pm
Contact:

Post by SleepingAwake »

bhenry wrote:Thanks for the reply SA. Well, I already have the carbon and glass so I’ll take another look at this. I have 20 and 22 oz triax as well so I can mix and match and come up with something

Just curious what you were comparing to my layup to?

Cheers, Bill
I compared it to my freetourer with similar dimensions (105mm underfoot, 1850mm length). But I used the same flex profile for a multitude of freeride skis now.

24Dave
Posts: 108
Joined: Mon Oct 03, 2011 2:14 pm

Post by 24Dave »

FWIW, I agree with SA. If you are trying to lose weight with a carbon/glass layup and not get an overly stiff result, I would use carbon for your torsional stiffness and fiberglass in the O degree or longitudinal axis. You could cut your uni carbon in patches and lay it in on the +- 45 angles.

Thin fabrics and single layer unidirectional glass can save several ounces of resin weight in addition to lower fabric weight from a thick triax weave.

bhenry
Posts: 61
Joined: Thu Mar 01, 2012 8:49 pm
Location: Indianola, WA

Post by bhenry »

Well, my son came home for break with one ski. The other one is up at Mt. Baker after a deep day. So, we made a new mold top and bottom. Twin tip 140/115/135. The cores are same as above. My son used 22 oz triax top and bottom with 2" carbon tape on bottom. Mine are 6.7 uni/ 12 oz biax fg top and bottom. My version is a bit stiffer and actually about what I was hoping for( imagine that). We'll be out this weekend to give em a go.

Weight- mine- 1850 g
his- 1950 g

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