Ski Builders Forum

We've been getting pretty frustrated getting p-tex sidewalls to stay bonded to our top sheets. My roommate has moved on to wood sidewalls, but I don't really want to have exposed wood sidewalls, even if they're totally sealed up.

So I was thinking I could bag the ski to get the top sheet around the sides, and then at the same time press it like normal in our press to actually get the ski pressed right. Has anybody every tried this? I would have to have the core shaped perfectly, and positioned perfectly on the base or I'd have some big issues, but I can get that lined up easy. This way I can forget sidewalls altogether

This link was posted here on the SB forum last month:

http://www.freeshaper.com/snow/index.ph ... terview#p5

Way down the page (90%) you can see a black rubber ? mold used to form the upper layers into a cap construction.

No side walls to mess with, nice.

These guys have a nice shop set-up.

Double high, double wide press.

Notice the control boxes.

Heat the skis from both sides.

Lay-up two skis side-by-side on an aluminum sheet cassette.

nice logo to...a respirator mask!

-S

still need details on what this mold is made of. High durometer RTV silicon or urethane is my guess but frenchy never told us.

It says it's silicon, so maybe RTV... no big deal to do actually, just need a lot of RVT silicon.

"on a aussi fait quelques moules en silicone nous permettant de faire des ski monocoque mais avec une construction sandwich" means : We also made some silicon molds that allow us to make cap skis with a sandwich construction.
(I'm French, it helps with translation...)

SHIF wrote: These guys have a nice shop set-up.

When this was first posted I thought the same. Although this time around I just noticed the cylindrical end stops for the bladder hose.

Anyway cool idea with the top mould.

that's not really that much silicon or rtv. It would not be really that hard to make those you just need to have a ski shape to mold.

SHIF wrote:This link was posted here on the SB forum last month:

http://www.freeshaper.com/snow/index.ph ... terview#p5


nice logo to...a respirator mask!

-S

hello
is an article I wrote on the french ski brand "white crystal" for freeshaper.com, they were very cool because they have answered at all questions and especially give lot off great photos! (Thank you again!)
and the respirator mask is the logo of "freeshaper" not at "white cristal"

I just made a snowboard, and a pair of skis using "cap construction" and the following technique:

- Vacuum bagged.
- Cut the cores out before the bases, and then used the cores as a pattern for the bases.
- Put an angle on the sidewalls before pressing.
- Rounded the corner on the top of the sidewall to allow for the fiberglass to bend around the edge.
- Getting everything aligned in the press was not at all difficult (vacuum bagging lets you shift things around after everything is bagged up if necessary)

Some comments on the process are that the first pair turned out worse than I anticipated. I had some topsheet material I got from a friend that turned out not bonding well, and being too stiff to bend around the edge, so I didn't get any pressure on the sidewall fiberglass. After pressing, I ripped off the topsheet, and had to press again to get the fiberglass on the sidewall to bond to the sidewall. I also had a little trouble with leaks in the vacuum bag and low pressure. The second pressing worked out alright, but I ended up having to cut off quite a bit of the sidewall fiberglass that didn't bond. The skis work well anyway though, and the girl I made them for is quite happy with them, so all was not lost .

The snowboard came out almost perfectly. We didn't use a topsheet, and the fiberglass bent nicely around the corner, and bonded to the glass under the core. The key here was to make sure that the base (with edges on) is a little wider than the core so that there is space for the top glass layer to bond to th e bottom glass layer and seal off the core.

Finally, the finish work using this method is a breeze. I found that the most effective way to remove the glass is to first cut off the excess with tin snips or strong scissors, then finish the job with a saw and a file. The best part is the amount of waste and unhealthy dust that is eliminated using this method..

But that was vacuum bagged only?

That only gives you atmospheric pressure (~14psi and change) and I want more, hence bagging AND pressing.

I did a few sample pieces trying this technique this weekend, I'll get some pictures of the pieces soon.

I got a small sample piece of the topsheet material that SnowboardMaterials prints on and used that. I did one piece that was a mid-ski thickness (~12mm or so thick), and one that was a tip thickness (~2mm).

On each of these pieces I did one side that had a steep side (basically vertical) and one side with more of a 45 deg angle to it. Both sides had a nice soft rounded corner (radius about the thickness of the core). Also on the thicker middle piece, on the steep side I gave it some extreme "sidecut" (a radius of about 12 inches maybe) as sort of a "worst case" of side-steepness, and sidecut, to see if the top sheet material would form to the shape without wrinkling. It formed perfectly, so it'll be fine for my skis.

I cut both pieces in half to get a cross section view of how things went inside the pieces.

My only issues (they're minimal) are:

-The top sheet gets a LOT of fiberglass texture in it. This might be a little better if I do the longitudinal fibers on the inside (towards the core) rather than outside (towards the top sheet). Seems like the diagonal fibers are a little better laid out in my glass so I should get less texture.

- On the steep side on the thick piece, the vacuum bag wasn't able to get the top sheet sucked completely down, in the corner between the core and the base/edges there is maybe a 1-2mm area that is filled with epoxy. I am not sure if this would be a good thing (long "rail" of epoxy to help with impact resistance maybe?) or a bad thing (brittle epoxy prone to cracking under flexing). Also the test piece I made is only about 4 inches long... I'm not sure on a whole ski if this epoxy void would be consistent. It does look great from the outside though.

The side that was cut at 45 deg was perfect, I just don't quite want THAT much chamfer/bevel on my skis, so I might go with a happy medium.

Will try to post pictures this afternoon.

Greg wrote:We didn't use a topsheet, and the fiberglass bent nicely around the corner, and bonded to the glass under the core. The key here was to make sure that the base (with edges on) is a little wider than the core so that there is space for the top glass layer to bond to th e bottom glass layer and seal off the core.
..

Question about not using a topsheet.... If the top layer is fiberglass (or fabric) what did you cover it with when you put it in the vaccum bag? Wouldn't the epoxy bleed through the fiberglass and stick to the bag? I'm assuming it would. I want to use fabric for a topsheet in a pneumatic press but unsure what to cover the fabric with so the fabric won't stick to my press. Could you describe the layup? I'd appreciate any info you can pass on. Thanks.

I found this post... http://www.skibuilders.com/phpBB2/viewt ... c+topsheet

In th epost above BigKam peeled away the topsheet to the graphic layer underneath. Then applied a new graphic over the old graphic using epoxy. Then used parchment paper over the new graphic and re-pressed the ski with the parchment paper in place.

we would have cured epoxy all over our garage if it weren't for parchment paper. that stuff is awesome and the epoxy doesn't stick to it!

plus its used for cooking in ovens, so it can easily withstand whatever temperature you're pressing at!!!!

Thanks for the info. I'll stock up on parchment paper.

Hey guys,

I have been looking at the forum for a while now. One question still bugs me and I cannot find an answer. Going back to twizzstyle's post, does enyone know how exactly a cap cassette like WhiteCrystal guys are using would work in a press?

I mean, if it is rubber, how would it exert pressure past the sidewalls? Would't it just deform?