Why so much pressure?

[bcohen5055]

I've been reading a much as I can lately about building skis and am planning to build a few pairs over the summer.

I'm an engineering student and have been involved with a lot of composites work including wet layups, prepregs, and vacuum infusion methods. As such I'm very confident in my skills involving vacuum bagging parts. I've seen various people on this forum be very successful with vacuum bagging skis but it appears that a pneumatic press is always the preferred method even in industry. When it's been discussed in the forums the answer for using pneumatic presses is always that it can provide more pressure, but there is never a justification of why all that pressure is needed. My first thought is that the stiffness of the core makes it difficult to conform to the mold shape but I'd like to hear from some of the more experienced builders if anyone knows.

Thanks!

[twizzstyle]

This is a highly debate topic, with lots of (sometimes uneducated) opinions. One theory is that higher pressure gives you more squeeze out, and therefore lighter skis. But using a less viscous epoxy will help with some of that.

Since you've got so much experience vacuum bagging, surely you know about autoclaves, so that should give you another data point.

If you're already great with vacuum, I'd say just stick with that. Saves you the hassle of building a press.

[sammer]

If you can bend your edges, cores and materials precisely Vacuum will work just fine.
Higher pressure gives you a better chance of really squishing your materials into your mold.
I've had a few problems that would have been non issues with more pressure, mainly edges bridging.

I've been using a refrigeration style vacuum pump since I started and it works fine as long as everything fits tightly without pressure.
If your prep is good the vacuum is pretty much just holding it all together until your epoxy sets.
Nice even clamping!

sam

[bcohen5055]

Thanks for the helpful info I've been thinking it over and I'm gonna go with vacuum. As I start to design the mold are there any limitations I should think about in regard to how much camber, tip, and tail radius I put in the mold. I know I'm going to get camber loss but is there a certain safe operating limit with vacuum or is it more experimental. Also for a first set of skis is it better to go with something simple like zero camber? I see a lot of people starting out this way.

[Huck Pitueee]

With the triax available it's very thick and needs lots of resin to get a full wet layup. So more pressure compresses that big mess of glass and uses less resin. I'm going to more and thinner layers for my next boards. I use a 3 layer core in vacuum pressing and the rocker or camber comes out perfect.

[Huck Pitueee]

Put what ever shape you want in the mold and if your core isn't fighting you it'll all work. That's why I use 3 thinner layers for the core. I also pin nail my layup to the mold so nothing moves before bagging.