Ski Builders Forum

Brazen wrote:You can use mylar in place of a topsheet in the press, then pull the mylar...comes right off. Leaves a great finish.

True! Gives a great shiny finish

So the Mylar will give the epoxy a shiny finish instead of dull like with the parchment?

Polyprop, used by florists to wrap flowers. Long lengths and about the right width. Just need to check the quality of the material.

Suspect there will be issues with UV damage long term ... will be issues with edge strike, if anyone is thinking this is a straight out of the press solution. It should provide an ideal surface for obtaining a smooth flat final finish.

I've not made a CF ski yet, but I did just get some in the mail last night, so soon (hopefully soon enough to ski 'em once or twice before summer sets in). I will say with FG that using release film for vacuum bagging in place of the top sheet gives a really nice finish (and you don't have the weight of a topsheet).

I'm going to do a uni carbon, +/- 45 biax FG stack. Not decided on whether the FG or CF will be on top. I plan to do a test layup with each and see which looks better, then make the bottom symmetrical.

^^I am planning a hybrid lay up like that as well to see if
1. It's lighter than a full glass layup
2. More pop than full glass
3. Stiffer than full glass

I was thinking about 9oz uni carbon and 17oz -/+ 45 glass. I might throw some carbon tow on a 60 deg angle also to be sure it it torsionally stiff enough.

I'm going way lighter than you.

If you look at the breakdown of triax FG, it's something around 50/50 for what's in the 0deg vs. +/-45 direction. It's a little off from this, but I can't remember which is which or what's the site that actually has it laid out to look it up again and don't have the time to search right now.

So, for a 22oz triax equivalent, let's say that's something around 11oz in the 0deg and 11 in the +/-45deg. Assuming CF is 3x as still (like the beginning of this thread asserts), I've gone with 4.4oz uni CF (which should be equivalent to about 13oz FG) and 12oz bias FG. I was going to get 9oz bias but fiberglass supply was all out (this is for a pair of backcountry skis). So I think I can get away with a slightly thinner and/or less stiff core (material) and get ~equivalent stiffness to the aforementioned 22oz triax that I've used in my previous skis.

If you're using 9oz CF and 17oz bias FG, you're going to be heavier for your composites versus "normal" weight triax so, if you change nothing else for the design I'd wager that

1. It's heavier than full glass
2. I know nothing of pop, but I'd guess there'd be more
3. It will be much stiffer.

but I suppose your could win on weight depending on the density/stiffness of the core you're comparing and if you use a thinner core. I haven't done the math (I'm sure someone has), but since stiffness is proportional to the square of half the thickness of the core, I tend to think that you win the most on weight while maintaining stiffness by staying with about the same thickness core and using a lighter composite stack. Obviously this is more true for a lighter core than a heavier one.

Great info FD. I'll have to think this layup out a bit more I think.

I did a layup with 12oz biax and 5oz uni carbon, turned out a little soft with my core profile so I put a wood veneer topsheet and the ski is a great lightweight med stiff backcountry ski.

MM, did you use the same core to get the slightly floppier skis? That's actually what I'm looking for since my backcountry boots aren't super beefy (Dynafits Zzero4)

Pressed the skis, no topsheet. Flashed, flexed and put a wood topsheet on to finish the stiffness. Comprende

MM do you think the 12oz with something beefier like 7 or 9 oz carbon would have done the trick? How thick of a core did you use? Maybe throw some carbon tow in on the 60deg axis?

Or maybe the 17 oz biax with the 7oz carbon?

I'm going for the proverbial lightweight beefy backcountry ski with this build.

Yo comprendo your layup. What I'm wondering was what the core dimensions were compared to a full FG ski that *was* stiff enough prior to the wood topsheet. If such a thing ever existed, that is.

IOW, when you say

turned out a little soft with my core profile

do you mean you used the same core profile as other skis or did you make a special (thin???) one for these skis?

Really appreciate the input, BTW.

Yeah standard core but .5mm thinner. 2-11.5-2.2 ski dims were 135-106-122 @188cm and core was 168cm core profile also had a flat spot set back from center and about 30cm long.

Schweet. Good to know. That helps with my design. I think my initial attempt to use some leftovers as an extra thin core isn't going to happen. Thanks again.

I'll likely just go with my standard core of 2.2/12/2.2 and use the 12oz biax and 7 oz uni carbon with some 12k tow on the 60 deg axis. I will probably put an extra layer of glass underfoot as well for extra beef in the binding zone.

My core will be basswood with maple finger jointed into the binding mount plus a perimeter stringer of ash. I think I ca get a nice light yet somewhat stiff touring set up with this config.