Ski Builders Forum

dude, the hose guarantees uneven pressure, because it is made out of rubber and coated with fabric. If you sandwich a piece of anything between your air bag and a solid bottom mold the airbag will distort slightly around the edges of what you put in there. Unless, your air hose is completely inflated before it makes contact with the piece in which case a very small area of the hose would even be making contact.

When the bladder is filled with air it obviously wants to expand. Without a cat track it will expand more where there is no laminate.

Grab a business card and squeeze it at the sides. The middle goes up. If the pressure is higher on the sides than it is in the middle there is the possibility of the laminate coming out concave. There are obviously a lot of factors, but this is an important one.

doughboyshredder wrote: If the pressure is higher on the sides than it is in the middle there is the possibility of the laminate coming out concave.

That's just the thing though, the pressure isn't higher on the sides, its all the same. The pressure is constant throughout the hose, and exerts a force exactly normal to the surface of the hose. So when we're pressing at 50psi, we have 50psi pushing straight down on the top of the ski all across the width, and any amount of the hose that bends around the sides will exert 50psi there as well.

Also, its not like the hose is bending completely around and pushing on the sides, it expands slightly past the sidewalls, but only slightly. There is no contact on the side of the sidewalls.

without a cat track there will be 50 psi that is affecting the laminate in a different orientation than directly down. So, the sidewalls are receiving pressure from the top and side, which means more pressure than the other areas of the laminate. Where the airbag distorts around the side of the laminate it will cause pressure to be exerted towards the middle of the laminate instead of the bottom of the laminate.

Hey, if it works for you without a cat track and you're happy with the results, that's all the matters.

In trying to determine what is causing the problem on these specific skis we have pretty much ruled out everything, except not having a cat track. The cores are flat and routed out for the edge tines. The mold base is flat, etc.. The only question is the lack of a cat track.

So, twizzstyle, what do you think is causing the severe concavity in these skis?

twizzstyle wrote:. There is no contact on the side of the sidewalls.

I didn't catch that first time around. It sounds like in your situation the effect I was describing is not happening. If your hose is inflated enough to make complete contact with the ski and not contact the sidewalls, then that is not the problem I am describing.

Like I said, there are a lot of factors.

I think it goes without saying though, that using a cat track is better than not using one.

doughboyshredder wrote:
So, twizzstyle, what do you think is causing the severe concavity in these skis?

I personally think it was our mold. Unfortunately we trashed it after the 2nd ski, so I have no way of knowing for sure Guess we'll have to see what happens with the next pair.

I have proof that if your airbag goes beyond your "rails", it will cause pressure voids, mostly in the topsheet.

If using sidewalls, it will create what I like to call a "cap-wich", the airbag tries to bend the topsheet down over the edge of the sidewall and make a cap,

at the same time this is happening, just inside the sidewall, LIFT gets created.

We could cover the physics...but i dont feel like it. Just trust me.

Though, in a CAPPED board, you may WANT to try to do it this way.
But in doing so, keep in mind the air bladder will squeeze down on EVERYTHING. If your core is not perfectly smooth, free of lumps, chips etc, if your inserts are not exact height of the top of the core, if your topsheet material is not smooth and somewhat rigid, if you have a speck of dust on your airbag, etc, everything will translate into lumps, pockets, etc.

With a sidewall, "sandwich" construction, you want the top to act like a plate, only forces pushing straight DOWN. However, for tips and tails you want that downforce to be down normal to the mold surface. BINGO, cat track is your solution.

Though, you could probably do the same with a thicker metal plate, like 14ga steel pre-bent (i would slightly over bend it), but you're going to find that using steel bars as a cat track, with a makeshift "cassette" (top/bottom sheet of 16-18 ga steel or aluminum slightly thicker) will be the best way to translate bag force into normal downforce.

OK! and on with the show...

this ski turned out fantastic! even better than the first two!
but the core shifted forwards during the layup or move into the press. so, with the binding inserts, the binding is sitting about 1.5" forward of the center (the inserts were center mounted). this also made the tail of the ski softer than expected and softer than the tip (symmetric profile) likewise, made the tip stiff.

dimensions: 155-130-145 182cm

on with the pictures...

Spruce and Maple core... 2 maple stringers



two cores ready (but only one worked. one of them, I mixed the epoxy wrong while gluing on the sidewalls.)


profiled...






inserts for my alpine bindings


did the countersink by eye


filled the inserts with candle wax


a small gap in the sidewall... didn't seem to cause any problems


layup




out of the press.... 50psi @ 200*F




it dulled the bandsaw blade so fast! oy!


rough cut, now its time for the bench sander


sanded and ready for bindings


i used an oversized bit to drill through the topsheet and glass and a slighly smaller bit by hand to clean out the candle wax.






so because the core shifted, im making two new skis of the same dimensions wood and everything and will glue two inserts to the base to make sure it doesn't shift

i took the one ski up for 5 or 6 runs. if it weren't for the soft tail/stiff nose and the bindings being forward mounted, this would be a fantastic powder ski. it has a slight early rise and no camber. the base turned out flat (without a cat track, perhaps because of its width). and hasn't show any delamination around the sidewalls like we experienced in the other skis. i was sure to flame treat the top and bottom of the sidewalls after profiling.

And next up while Kevin gets his new pair ready to go, I'm getting ready to press my next pair, almost as fat as his, but much shorter...

150-135-140, 160cm in length VERY soft tip and tail.

Very beautiful ski! Good work.
And what their rigidity?
Could not show a photo as they to bend?

Why do you guys need skis so big for Snoqualmie....

Damon wrote:Why do you guys need skis so big for Snoqualmie....

Shut your face damon!!!

I finally got my new pair pressed (I only have pictures of the first ski right now... and I'm away in kansas for work so I can't get more).

They're called the Piggy Sticks

160cm
150-135-140

They are reverse camber. They are a little bit stiffer than I wanted. They are softer than a K2 Public Enemy, but stiffer than my Line Motherships. I am going to make another pair but make the cores just a little bit thinner and I think they'll be spot on.



mostly spruce cores, with two oak stringers







The left ski says "Piggy" on the tail (rice paper) and the right ski (not shown) says "Sticks"





Hopefully there will still be snow when I get home from Kansas in a few weeks so I can try them out.

I used QCM epoxy for these skis, and up until now we've been using FiberLay epoxy. I like the quick setting nature of the QCM (~30 minutes at 170deg, vs 6-8 hours for the FiberLay) but it is MUCH thicker than the FiberLay, so I had a hard time getting the fiberglass to wetout like I normally like it (so you can see the fiberglass quite well over the black tips/tails.)

what QCM mix are you using? My EVH 0043 is thick as hell, but when mixed with ECA408 which is practically water consistency, the two mix together into something quite manageable.

I am using the 0043 resin and ECA032 hardener. I warmed up both of them in a bucket of hot water for the 2nd ski, and that helped a lot, but it was still thicker than I prefer and am used to. I could heat them up more, but I don't want to heat them TOO much and speed up the set before I am ready!

try the eca408 if you want better viscosity

i might try what you're using, i'd like to experiment with a thicker mix

what i'm really really trying to get a hold of is some huntsman samples, but they wont even call me back!!!