Ski Builders Forum

When laying up glass, is there a top and bottom to the glass cloth or doesn't it matter?[/img]

From past experience and from others in the forum who work with composites, you want the same face of the material against the core. I use trixial FG. If you look at triax, one side looks more finished than the other. I have the more finished side away from the core. So, the finished side is face up on the top of the core and face down (against the base) on the bottom of the core.

Thanks I was thinking it something like that but wasn't sure.

The triax is matted and stitched usually rather than woven so I usually put the 0 degree towards the core on top and bottom.
I dont know if its right.

I do the same as MM
Asymmetric composite layups (whether that be actual different weights or types, or just the triax laid assymmetrical) can affect camber when heat curing. Apparently.
I think it's a good idea to lay the triax symmetrically about the core, but there are plenty of commercial makers that use carbon stringers either just above or just below the core.
I think having the longitudinal fibres laying against the wood core is the way to go, based entirely on a hunch/feeling rather than any science

Interesting, I'd never even considered that. I'd be interested to see how back to back tests perform.

My hunch is you wouldn't be able to tell the difference, but it can't hurt to do it the way you guys have been.

The key point is if your curing with heat or not. Because the CTE of the fibers change with orientation, you can end up with twisting/warp.

I also have an issue with manufactures putting the carbon stringers on top of the core - pure marketing move. The stringers are more effective underneath the core as it will put the fibers in a greater tensional loading.

What Damon said. I tend to belabor this point a lot on the forums, so I'm glad people keep this in mind. If youre not using heat it's basically no issue (not entirely, once you get to the cold mountain you may still get some camber changes) but if you cure with heat, it's more likely to cause noticeable changes in camber.

Also, if you do a symmetric layup, a ski with the longitudinal fibers (assuming triax) out from the core will be stiffer than a ski with the longitudinal fibers in towards the core. Small difference, but a difference nonetheless.

Thanks guys longitudinal fibers towards the core it is then. This might explain part of my extra camber in my first set.

twizzstyle wrote:
Also, if you do a symmetric layup, a ski with the longitudinal fibers (assuming triax) out from the core will be stiffer than a ski with the longitudinal fibers in towards the core. Small difference, but a difference nonetheless.

Exactly. If you want a stiffer ski torsionally put the 45/-45 away from the core. If you want stiffer ski longitudinally put the 0 away from the core.

Carbon stringers on top are NOT a marketing ploy. Especially in a rockered layup. Yes, carbon is only stronger than glass in tension but a ski flexes in both directions. In most situations carbon is more effective on the bottom of the core, but not in all. Imagine a camber ski with carbon on the top. Straight lining a bumpy runout at speed tensions the fibers above the core. A rockered ski with carbon on the top retains it's rocker more, and is less floppy, as to flatten out, it tensions the fibers on the top.

Damon wrote: I also have an issue with manufactures putting the carbon stringers on top of the core - pure marketing move. The stringers are more effective underneath the core as it will put the fibers in a greater tensional loading.

I've prototyped a lot of skis with all sorts of configurations. No carbon, carbon on top, carbon on bottom, both top and bottom, different width carbon top and bottom, full width.

Our favorite layup is still carbon on top, and there is no question in my mind it makes a huge difference vs going with no carbon. Without carbon our skis are noticeably less stable, less damp, less responsive. Think wet paper bag by comparison.

We've liked how our skis ride with it underneath the core, they are definitely a bit more responsive and poppy - so good for park/jib skiing - but we also find them less damp, less stable, and not as easy to ride, so less fun on the rest of the mountain.

Carbon on the top, combine with bamboo, gives what we have found to be the best combo of responsiveness and dampness. Skis haul ass, are super stable and don't feel every little bump like you do on some lighter wood cored skis, but are also playful, responsive, and just fun to be on.

So as a manufacturer putting carbon on top of the core, let me assure you it isn't purely a marketing move (I wouldn't spend this much time building skis I am not happy with). Heck, it is probably the opposite of a markering move since everyone always wants tells us how we are doing it wrong.

I just let them know it skis better, and that is what matters to us.

That said - we've been getting some cool new stuff from vectroply to try out, and are always trying to tinker with stuff, so if we find something we like better, we will change to it, regardless of what it is.

Scott, there are very few who get to try layups like that - I'll definitely take your word. I've always liked skis with carbon under the core, but I've never been able to do a direct comparison like that. I'm curious - what modulus fiber do you use? And what size rovings?

But I'm still convinced there are better materials to use on top of the core - fibers (or topsheet materials for that matter) with higher compression and impact toughness. DBS, I can see your point on rocker layups though.

And your a manufacture with an asterisks because you don't have the "viewing port" on your topsheets to let the world know about your carbon stringers.

doughboyshredder wrote: If you want a stiffer ski torsionally put the 45/-45 away from the core. If you want stiffer ski longitudinally put the 0 away from the core.

This is typically a thing that should be in a wiki!
(among other things)

Another thought on carbon tows in symmetric layups...putting the carbon on the top resists contraction of the top and seems to increase expected camber. Reverse is also true.

I find I fiddle with the location of the carbon tows more for this (and, I admit, looks) than for anything else. Unless strength is a big issue, in which case i out the carbon underneath.

Another thought on carbon tows in symmetric layups...putting the carbon on the top resists contraction of the top and seems to increase expected camber. Reverse is also true.

I find I fiddle with the location of the carbon tows more for this (and, I admit, looks) than for anything else. Unless strength is a big issue, in which case i out the carbon underneath.