new skibuilder

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szymon
Posts: 24
Joined: Wed Dec 09, 2009 3:32 pm

new skibuilder

Post by szymon »

Welcome everybody!

I'm following the discussion on this forum for quite a long time, and for some I'm trying to make my own skis as well.
Thanks for everything I found here - that was extremely useful.

I would like to present some photos of what I've been doing. I didn't make a lot of pictures during the work, but I do got some.
Of course I had huge problems with all the components (like everyone:)
I decided to start with a pair of true twin tip freestyle skis. I thought they will be easiest to make.

I've been working on SnoCAD-X, I switched to Rhino now (still using some SnoCAD to do some beginig designing)

I cut mold on CNC (one piece and then I copy with the router)
I made a profiler (designed by one member of this forum) - thx, it's working OK, but I'm withink os sth else (maybe home made CNC)
My big pain in the *ss is edge bending. I made myself an edge bender like the one in SKEVIK movie, but still, matching perfectly takes me couple hours and it's the only part I don't like in skibuilding process.
I was first building cores from single stringers, now I do it with blocks which I later have them cut into planks.

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Some test how materials bonds together:

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UHMWE sidewall - didn't bond well...
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Now it's time for some freeride skis 139/120/136

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My two big issues right now is:

- how to hold still base with edges atached - in the casette and how to hold core. The way I do it (on the photos) is no good, because sometimes the base pops up from the little things that holds them and the edge with base goes over and get bend (like concave)

- When I ski on the finished skis and I hit one with the another the fiberglass in this spot turns white. It cracks and layers of fiberglass separates. While I was doint test I coul tore apart fiberglas into two layers (photo)
Is the possible cause could be the fiberglass? It's quality is superior, but it's 812g/m2 - maybe It's too thick? Or can it be epoxy, pressure (i press at 65 psi) or sth else?

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Thanks again!

twizzstyle
Posts: 2203
Joined: Tue Mar 07, 2006 8:25 pm
Location: Kenmore, Wa USA

Post by twizzstyle »

Welcome to the forum! Not too bad for your first few pairs! I've always done full wrap edges in the past, with results about as good as yours (which is pretty good). For the last two pairs I did 3/4 wrap, and it took those ~2 hours I was spending bending edges, down to about 15 minutes. You should try that next time, saves a TON of work.

As for your sidewall bonding issue - did you flame treat the UHMW before bonding?

Crazy that you're able to just pull the fiberglass apart. My first inclination is that you are a little epoxy-dry. In the photos of the first skis I can see quite a bit of dry fibers. You might use a little more epoxy, and maybe a little less pressure?

Either way, you're doing the testing right, and learning all the same stuff we all do when we start. Nice work!

szymon
Posts: 24
Joined: Wed Dec 09, 2009 3:32 pm

Post by szymon »

nice to hear that twizz - thanks

I'm thinking very much about doing 3/4 wrap, but I'm not 100% sure about bonding all layers perfectly, so for now I'll stick to full wrap. In future I'm sure I want to do 3/4 wrap - I believe it's better and looks better.

Yes - I sanded (60g) and flamed the UHMW before bonding. I'll try to watch some movies on you tube about that. do you use UHMW?

I don't think I use to little epoxy (for last pair of 191cm freeride skis I used 1100gr of epoxy), but maybe. When I pour the fiberglass with it I later take out all the epoxy that isn't inside fibers - shouldn't I do it?
Don't you think that less pressure can cause worse bonding and not precise enough bending to the mold? (especially in the tip and tail area)? What pressure would you guys recommend? I would do some testing.

thanks again!

Sherpa Burns
Posts: 73
Joined: Mon Feb 07, 2011 8:39 pm

Post by Sherpa Burns »

Actually, too much pressure can squeeze out too much epoxy and make the laminate weaker. I press at 50-55 and everything comes out well bonded and flat. I tried going up to 65 in the past and when I did a hard hand flex I could hear a little too much cracking.
I think your fiberglass seperation could only be one of two things: too much pressure or the resin wasn't spread out or wet out through that area. What epoxy are you using?

szymon
Posts: 24
Joined: Wed Dec 09, 2009 3:32 pm

Post by szymon »

I use Hexion MGS L285 epoxy with 285 hardener. It's the german epoxy which is f.e. used and certified by German Federal Aviation Authority for building small planes.

jellyfish
Posts: 27
Joined: Wed Oct 27, 2010 5:05 pm

Post by jellyfish »

Sometimes if it's a cold cure and your core is dry, the extra Time it takes for the epoxy to cure is enough time for the dry core to soak up extra resin and create a dry laminate, the lightest laminates can be archived by sealing the core prior to layup I've even heard of model aircraft builders useing hair spray to seal the core before laminating. if I could make another observation it seams you have wetted out your entire reinforcement , it may not have been on purpose but the extra cure time which allows the resin to travel with capillary action to  the surrounding dry fibers you may have to find a way to prevent this from happening.

Cheers
Jim

James Everding
Jellyfishboards.ca
519-496-5359

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falls
Posts: 1455
Joined: Tue Oct 27, 2009 5:04 pm
Location: Wangaratta, Australia

Post by falls »

I don't think I agree with the hairspray idea to seal a core. Hairspray is often used as a ghetto release agent, so sure it would prevent epoxy going into the core, but it wouldn't be great to keep your layup together! Sometimes model aeroplane components are made on a "core" that is pulled out after the epoxy cures.

PS. I had the same white spots at the edges on my first pair of skis with a clear topsheet where they banged together. I used west system epoxy for them. I haven't made any other clear topped skis so can't say if it is still the same in my newer pairs with ski specific epoxy. I wondered if the west was too hard (ie. not a more flexible epoxy) so with impacts it tended to crack where a ski specific epoxy would have flexed better. Just a theory. The other thing is as the others have said maybe you haven't wet the glass out thoroughly enough.
Don't wait up, I'm off to kill Summer....

jellyfish
Posts: 27
Joined: Wed Oct 27, 2010 5:05 pm

Post by jellyfish »

Hairspray to seal a core is totally doable just need to find the right one just an example of people thinking outside the box , with a cold cure that soak time makes all the difference in the world find a way to limit epoxy obsortion into any substrate and you will make a lighter better laminated product.

Jim

szymon
Posts: 24
Joined: Wed Dec 09, 2009 3:32 pm

Post by szymon »

What do you mean by cold cure? I use heated press and I cure in 65 C - it is the temperature that is recommended by the manufacturer.
But the idea that dry core soaks some epoxy sounds resonable for me; however I don't know about the hairspray...
About that I haven't wet the glass enough - last time I was really focusing on that and I thought it worked well, but...
What tools do you use to wet fiberglass? just spatula or some kind of roller to push epoxy hard to the glass?

@jellyfish: "if I could make another observation it seams you have wetted out your entire reinforcement , it may not have been on purpose but the extra cure time which allows the resin to travel with capillary action to the surrounding dry fibers you may have to find a way to prevent this from happening. "
-what do you mean here by reinforcment? carbon? So do you suggest for me to wet carbon for longer time? Did I understand well?

rockaukum
Posts: 558
Joined: Fri Nov 03, 2006 9:23 am
Location: Placerville area

Post by rockaukum »

reading your post there was a concern about how to hold the base material in place on the cassette. Try using a spray glue on the base material. Should work just fine. Cleans off with your initial base sand. On locating your cores to the base, I route the core for edge relief and also use locater pins attached to the base.
ra

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MontuckyMadman
Posts: 2393
Joined: Fri Jun 20, 2008 9:41 pm

Post by MontuckyMadman »

Is that epoxy formulated for compression molding? Looks like a squeeze out issue.
sammer wrote: I'm still a tang on top guy.

gozaimaas
Posts: 655
Joined: Fri Feb 10, 2012 4:17 am
Location: Nagano Japan

Post by gozaimaas »

rockaukum wrote: I also use locater pins attached to the base.
I would love to see some pics of this system. Do you superglue a small dowel to the base before the resin is applied or something?

twizzstyle
Posts: 2203
Joined: Tue Mar 07, 2006 8:25 pm
Location: Kenmore, Wa USA

Post by twizzstyle »

gozaimaas wrote:
rockaukum wrote: I also use locater pins attached to the base.
I would love to see some pics of this system. Do you superglue a small dowel to the base before the resin is applied or something?
Here is a picture of one of my old skis with locator pins. I use 3/8" dowel, superglued to the base just prior to layup, and drill holes in the core. WOrks great, I just have to cut two small holes in the bottom composite layers to go over the dowels.

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gozaimaas
Posts: 655
Joined: Fri Feb 10, 2012 4:17 am
Location: Nagano Japan

Post by gozaimaas »

Awesome, thanks mate.

jellyfish
Posts: 27
Joined: Wed Oct 27, 2010 5:05 pm

Post by jellyfish »

Looked at your resin low viscosity and a long time to gel is very similar circumstances to a cold cure, this is how it looks to me your fiberglass reinforcement outside the ski is saturated and even puddled, your resin has a viscosity of 700cps at room temp now heat it up to 60*c and my guess it is like water give it 40 mins under pressure and your resin was pushed out of your ski before it cured. This is how it looks to me.
Hope you sort this out, sorry for any confusion
Jim

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