Forward shift in camber

[FlamingYeti]

Hey guys,
So we just finished up our fourth pair and we are finally starting to get to the point where the skis look good. There was a rather strange problem with this pair though. We designed the ski to have 7 mm of camber directly underfoot. The mold/form was made with that same profile. However, there is no camber whatsoever underfoot. Instead, the camber moved about 35 cm forwards of the centerline. Here, it has about 4 mm of camber. The tip has the same amount of rocker that we designed it with, but the early rise was hindered a bit. The mold is exactly how we designed it, but the ski isn't. We aren't pressing with heat and we are pressing at 50 psi. Has this ever happened to anybody? Any recommendations or ideas?
Thanks,
Chris

[gozaimaas]

Strange.
Do you have a rough idea what the ambient temp was when you made them?
What epoxy did you use?
Did you have problems with camber on the ther skis?

[FlamingYeti]

In our press, we can only do one at a time. We had the heater on in the garage for both skis and space heaters positioned around the press. For the first ski, I'd say the ambient temp was probably about 75˚ F. For the second, probably around 65˚ F. The epoxy we use is the Entropy Super Sap Resin with Entropy Super Sap CLF Hardener. We have had problems with camber, but only things like the contraction and instead of having 3 mm of camber, we have 0. I would post a picture, but I've never been able to get it to work.
-Chris

[Dtrain]

Weird. Are the tip height proper. Did the skis slide back in the mold. What core material, as was it laminated. Last of all, what kind at composites and where they the same on both sides of the core

[FlamingYeti]

Yeah, the tip height was how we designed it. the skis didn't slide back because the core was nailed into the mold. The core material was horizontally laminated bamboo, yet we laminated it vertically. The composites that we had were 1 layer of triax carbon (60-60-0) and 1 layer of triax fiberglass (45-45-0) below the core and 1 layer of triax fiberglass above the core.

[Dtrain]

If you we're using heat, I would say it was the carbon layer underneath that created this for sure. But without heat, still might be the case. I made a board last season with a full layer of 0/90 8oz on bottom and 21oz basalt 0/45/45 on top of a bamboo core. Base came out convex. After some special work on a base grinder I loved the result, but won't try it again.

I think it is safe to put a strip of uni carbon or some tow on the bottom, but ya, a full layer of multiaxial carbon on bottom and no the top is probably your problem. Some time these experiments can go awsome, other times leave a guy in tears scratching his head.

The only other thing I can think of given the description is the nail

[Dtrain]

Nails put to hold the thing down messed it up somehow, or you had some serious uneven moisture content in the bamboo.

Hope it all works out. Like an STD test. The worst part is not knowing.LOL

Derek

[FlamingYeti]

Alright, thanks for the info man. We'll try without the nails next time and a symmetrical layup and see where that gets us.
-Chris

[gozaimaas]

If you really want to know what caused it you should only change one aspect of the lay up. I would say keep the nails but go symmetrical with the lay up.
Otherwise you might have success but forever wonder was it it the nails or the carbon.

[FlamingYeti]

Excellent point. We'll try the symmetrical layup on this next pair in the same mold and see if it's still wrong. I'll do an update once we finish those up.

[barnboy]

Squatch Burn-

We've dealt firsthand with the creeping camber before, awesome right?

Goz has you on the right track, for sure go symmetrical with your lay up first, then start tweaking elsewhere. You'll have a good chuckle when you mount those puppies up and find the misplaced camber, while perhaps visually and emotionally off-putting, skis quite well.

Congrats on the progress!

[FlamingYeti]

So after we pressed an identical pair with symmetrical composites, the "creeping camber" definitely went down a bit. Instead of being 35 cm forward of centerline, it's now about 15-20 cm. We are now tossing out the core nails since that is just a bad idea. In this last pair, the nail decided to go through the base along with the core. Awesome… A new plan for core centering is in the works and will definitely help. Thanks again for the advice.

[MontuckyMadman]

Is the thickest part of your core at the camber point?

[originskis]

Dtrain- I've made multiple pairs of skis with 0/45/45 14oz carbon on the bottom only and have never had an issue with camber shifting. Just sayin'. Why would the carbon cause a shift? If he's had multiple camber issues I think it would be something related to the pressing cycle or perhaps the core- like montucky said.

[originskis]

The one concession I might have is heat cure, since that seems to be the only difference in what you've done and I've done, Yeti. I'd find it odd but the lack of heat could throw a wrench in things...