Ski Builders Forum

I've built a couple pairs of skis with nomex honeycomb cores. I'm worried about the screws pulling out because they're entirely carbon with a bit of light glass. The object here is a very light ski, so I'd like to determine which fiber is the most efficient at retaining screws (like the strongest resistance to failure in the normal direction).

I know that Ski Trab does this, but they don't label what their binding reinforcement fiber is on their schematics

A few options:
Fiberglass
Basalt (honestly not entirely sure how this differs from normal glass)
Kevlar

And I'm guessing these are not the way to go, but perhaps?:
Dyneema
Innegra
Flax

I'd put down carbon, but from past experience it doesn't provide much support to holding screws in the laminate

Thanks!

Unfortunately I have no data on the pull-out strength of those fibers. I think flax could work well too as the laminate usually stays relatively thick in a layup which would give the screws more material to bite into.

Other than those fibers the ski industry often uses titanal plates to reinforce the binding screw retention.

No fibre is really good for screw retention. If you wanna use fibres the thickness is the key. The thicker & denser the better. That said you can use pieces of quadrax glas or multiple layers of fine woven glas.

Titanal would be not so bad but titanal usually bonds not good, so you dont rip out the screw, you rip the screw with the titanal sheet (seen that on many old titanal boards).

Phenol is better if you wanna go this way. But still just a way to go around the main problem (weak core)

Best is to have a proper core material where the screws go in. Replace just the part of your core where the screws go in with some proper material (hard wood).

Or inserts ....

We had a discussion about this topic over at talkcomposites and i thought i would link it here for future reference:

http://www.talkcomposites.com/38146/Bes ... site-Fiber

Don't relay on fiber hiding your screws in. Place dense hardwood under your acres and you can have confidence in your screw retention. That being said. I have never tested different fibers for screw retention. I normally use a triax glass layer and an extra layer of biax under the mounting zone. To my knowledge no one has ever had a crew pull out of my cores. I use either ash or maple under my binding screws. No softer hardwoods like poplar and definitely no softwood or Paulownia.

If you use titanal make sure to use plenty of VDS and make sure it is properly handled and cleaned before layup.

I believe Trab uses a carbon fiber plate, which is numerous layers of carbon pressed with a very high density. Vinman is right, if you have a Nomex core under the bindings and have laminated the ski already, you should probably router out some channels and epoxy in some hardwood strips, then cover the deckside up with generous amounts of glass and feather the layers to prevent a kink in the ski flex where it might want to snap. Binding retention screws in a thin laminate layer over honeycomb will probably peel your topside laminate off of the Nomex in a fairly short time.