Ski Builders Forum

I know that there has been some discussion of delamination, and the key solutions seem to focus on material prep - my understanding is to focus on 3 steps:

1) Provide surface structure (Sand)
2) Degrease (Wipe with acetone or similar)
3) Flame treat

I did the first 2 of these, but not the third as my understanding is that unless conditions are very controlled then flame treatment can make things worse!

In spite of doing the first 2 steps, my bond was still poor in the tips (I am using ABS spacers and the bond to this surface failed). Thinking about it a little it is not surprising that the tips fail - think of flexing a pad of paper - there is no shear in the middle, but lots at the end. The bond at the tips may be as good at at the middle but it will fail there first.

So does anyone have any further suggestions for improving the bond or the design? I can think of / know of 4 possibilities:

1) The usual rivets at the tips. This is what most people do. I think that it has 2 effects. 1 - it holds the bond together and 2 (perhaps more important) it limits the shear.

2) Use rubber rather than plastic in the tip spacers. The rubber will allow shear deformation across its thickness and therefor reduce the load on the bond at its surface.

3) Use 'undersize' tipspacers. This will allow the two fibreglass layers to come together at the very tips of the skis (a bit like a cap construction) which should form a much stronger bond at this point and reduce the stress on the spacer bond.

4) Use wood tipspacers for a better bond.

I am leaning towards the idea of an undersize rubber spacer for my next pair, but has anyone found a good solution to this problem so far?

Are we all suffering delaminations at the tips?

Let me know...

B.

Bambi, I used glass and CAP (a polyester fabric). I can see and feel the end of my core. No de-lamb so far. The CAP makes the laminate tougher, less brittle. It is added as an internal layer or two from the core to the tip. Lays up like the rest of the glass. I just don’t have warm fuzzies about using plastics yet.

How did you get a you ski to de lamd already. Isn't this the first pair you've made? Did you give your ski enough time to cure completely?

Hafte

Thanks for the tip on CAP - I take it it is like a woven porous material? Where abouts do you get it from?

Delam - I flexed one ski with the tail on the floor and the area round the tail delaminated- oops!

B.

Did the epoxy seperate completely from the spacer leaving the ABS clean?

How long had it been since you mixed the epoxy when you did this?

Looks like it separated very clean - It had been in the press for 24hrs then another 24hrs before I flexed it.

Oh and I pressed at 35psi at 212 deg F for 2 hrs then dropped the temp to room temp.

B.

Bambi, CAP is a trademark name. Its a fabric just like glass, but its a synthetic like Kevlar. It’s nicknamed poor mans Kevlar. The funny part is it has almost the opposite characteristics. When laid up by itself it is very flimsy, but it will not tear ie very tough. It can be used in compression and tension equally well.

Here is my source. They are very good to work with. http://sweetcomposites.com/Polyester.html it’s the polyester fabric that you are after. Another thing that I have read about it is to try and keep it separated with layers of glass. In other words go poly/glass/poly/glass ect. Two synthetics can have bonding issues when next to each other. The last came from “The Boat Builders Manual” by Charley Wallbridge. Oh and the stuff will not sand or grind smooth. Keep it inside where you don’t have to worry about it. If it does poke out hit it with some epoxy let it cure and when sand/grind the fuzz off.

There is also some good info about glass, Kevlar and carbon fibers on this web site. Unfortunately not much about CAP.

That sucks about the delam (none of my spell checkers like the way I spell this). Hope you can fix it.

Hafte

Thanks again Hafte,

I'm sure that with a couple of rivets I can make something skiable - to be honest I am thrilled at the results of my first pair.

There was a lot that could go wrong, but aside from the bonding issue everything else looks good - everything aligned in the mold, the press held together, the heater got up to a decent temp and the flex of the ski matches what I had modeled/predicted.

If they end up on the wall as a souvenir then it is no problem as I have another 4 pairs of cores ready to press!

B.

P.S. How are the inserts working out for you?

P.P.S. I will probably be out in Salt Lake over Christmas / New year some time so we should compare skis if you are around.