Ski Builders Forum

Have a f.u. core from last season which my machine made too thin on some places. Its ash wood. Do you guys think its possible to use carbon (450g triax) instead of glas (750g triax) to compensate for the missing thickness?
Or lets ask like that ... how much can be a core thinner when using this carbon to get similar stiffness & flex? 0.5mm or more?

What about putting .6mm veneer next to the core during layup?

Good idea. But ... i like to experiment with carbon anyways and the material i already have laying aound.

what dimensions does the ski have? how thin is too thin?

CHeers

Too thin is up to 0.5/0.8 mm mid shovel (e.g 6 -> 5.5) on a superwide ski. Dont have exact measurements on hand, the core sits somewhere in my workshop since last winter.

Is there no thumb rule for glas -> carbon (like 15% less core)? Would be cool to have a starting point. From then its experimenting anyways...

If the core is less than 8mm that might be a problem. I think adult ski bindings are typically 8mm long. I don't have any info on wood vs CF.

But as for FG vs CF.... I've found that 9oz uni CF is about as strong as 22 oz triax FG in longitudinal strength. Since the CF I have worked with is Uni, there's very little torsional strength.

Hope this helps.

Adult binding screws are 9.5 mm long. If you core is less than 9.5 thick this is a no go. Junior screws are 7.5mm

Yea I measured one of my binding screws and it was longer than 8mm. Somewhere I saw an ISO std that an adult binding mount hole had to be at least 8mm deep into the core, I think a jr mount was 6.5mm or 7.5mm. When you factor in the binding mount plate and/or a full plate it makes sense the screw needs to be longer. As for the wood core I normally don't go under 10mm anyway.

The binding screws are no problem, the 6mm was mid shovel! Problem with my machine did create just problems in the thinner parts of the core, not the center. I will reshape the core so the original profile is back, the whole core will be then about 0.5 - 1.0 mm thinner (i did build this core profile with glass already and its perfect). There will be still enough thickness in the binding area.

But ... will the carbon stiffen it up enough, too much or ????

p.s. my binding screw drill bit makes 9.5 mm deep holes, thats iso standard like stated above

The last ski I built was pretty similar in dimensions to yours. Maybe a little thicker. My tips started as 1 to 1.5 mm.
In the layup. I added a 160g/m² layer of carbon weave to the entire length on the bottom and 200g/m² carbon on the front 1/4 of the ski.
Rest was 750g/m² Triaxial top and bottom and a layer of 320g/m² Biax under binding.

In my opinion they came out about perfect.
On the other hand, I haven't skied them, so I don't know what perfect is.

Not sure if this answeres your question, however the extra layers of carbon on the outsides will definitley help with stiffening your ski.

Lol, my denglish seems to lead to the wrong direction

Normally i use just 1 layer of 750 triax glas. Now i like to use just 1 layer of 450 triax carbon. In my opinion it would make the ski stiffer with same core dimensions.

So ... how much to shave off the core to get with the carbon same flex as with glass.

I want to see also the weight difference between these two setups with same core and wood, so i want to try a pure carbon layup.

Twizz is the carbon guru. But from my experience it's about 3 times stiffer than glass.
You will end up with a thin, light ski with crazy amounts of spring and life.
I make only boards and thin cores with lots of glass and carbon are super fast and lively beasts. Can be a real handful if you get lazy with it tho.

That would make sense. Friend said he took 1mm off his core profile and it was still too stiff.

So the 750glass -> 450 carbon should make it around 1.8 times stiffer (based on your x3 formula)

Maybe twizz chimes in

Just a quick point about core thickness and binding screws,

When I make kids skis the core is usually right on 7mm.
Once I add 19oz triax, an extra layer for binding retention, a graphic layer and a topsheet I've yet to drill thru with 7.5mm junior bit.

YMMV

sam

Right on Sam, I always figure .6 for the glass layers and . 6 for my veneer layer on top of my core.

For adult skis I never have a need to go less than 10 mm for he mount zone. Like you also, I use 19 oz glass for the shorter stuff to ensure they don't come out too stiff.