Solid fibre core

Egil · Post by **Egil** » Mon Dec 23, 2013 1:34 pm

Dear skibuilders from all over the globe, I’m new to the forum but definitely not to skibuliding.

Hopefully I’ve got the answers to many of your skibuilding questions.

I'm a former pro ski builder at Åre skidfabrik a small factory in Sweden (extrem, åsnes, hendryx skis, cmd) and I have built well over 10000 pairs of skis and a few hundred snowboards over the years.
All built with prepreg, CNC'd cores, diecut base and aluminium bottom+top mold in water heated hydraulic presses with both manual and CNC camber adjustment from Langzauner. I've also done most maintenance and repairs on all the machines.

Now as a hobbyist I'll go for vacuum infusion.
One reason for vacuum is that I've built to many skis in a pro press to go lowtech and I want to do something else. The other is that I see some benefits with vacuum infusion as it's less gooey than wet layup and you can adjust the amount of resin to perfection!

One thing that I'm totally new to is solid fibre cores.. And I've not found any posts about it here nor anywhere else but I might just suck at searching.

What I want to accomplish is a THIN! ski. I really don’t like thick skis, high bindings and I've always tried to stand as low as possible on my skis for best snow feeling.

My approach to this is to build the hole sandwich in one vacuum infusion.
The plan is to use use 2 layers of triax 450g CF top/bottom and instead of a normal wood or what ever core I'll just ad ca 12-15 layers of ud 300g flax centred in different lengths to build up a really thin and stiff core of 1-4-1 mm.

Has any of you guys tried anything like this before?

twizzstyle · Post by **twizzstyle** » Mon Dec 23, 2013 1:47 pm

Never seen anybody try that, but I'd be really interested to see it work! It's going to be a challenge to get enough stiffness while keeping it that thin, while at the same time keeping the weight to something reasonable.

I've never done vacuum infusion, but I've always wanted to give it a go in non-skibuilding projects... (female mold carbon fiber layups, things like that)

vinman · Post by **vinman** » Mon Dec 23, 2013 6:22 pm

what the of binding will you be using? standard adult bindings screws are 9.5mm long.

Seems like the minimum thickness would be 10mm for use with a standard alpine adult binding....

Am I missing something?

SleepingAwake · Post by **SleepingAwake** » Mon Dec 23, 2013 11:55 pm

with a core thickness of 4mm it will be a noodle. Even tough flax is way stiffer than a standard wood core, to get the same stiffness as a ski with 10mm wood core you need a 8.5mm flax core. And that will be quite heavy. Even if you go full carbon you still need a 6mm "core".

Thats because thickness is so important in bending.

And you would need more fibers at +/- 45° than usual, because the cross section is super important for torsional stiffness.

But apart from that, I've got quite a bit of experience with vacuum infusion. Feel free to ask if you wanna know something!

Egil · Post by **Egil** » Tue Dec 24, 2013 1:52 am

I'll be using M5 inserts and to fix them in the correct hole pattern I'll use a drilled titanal plate.

About thickness.
According to my calcs a 1-4-1 core and a total of 12 layers of carbon fibre equals a 2-10-2 core and glass but I'll redo that calculation.
First I'll just do a small test "beam" and measure it's stiffness.

I think I have the infusion part under control but we'll see what Mr Murphy has in his pocket.
Have you infused skis?

SleepingAwake · Post by **SleepingAwake** » Tue Dec 24, 2013 2:48 am

Ok, maybe there is a mistake in my calculations. I was a little in a hurry

Not infused any skis. But kiteboards and plenty other stuff (kind of my day job)...

Alex13 · Post by **Alex13** » Wed Dec 25, 2013 2:26 am

Welcome

I'm hugely interested in prepreg, to save all the mess, of course.

What kind of temps did you need to run in your press to get the prepreg to bond?

Sorry to hijack your thread - I'm a snowboard builder and a poor one at that - I don't have much specific to add to your questions.

Feel free to PM if you want to discuss this out of here.

MontuckyMadman · Post by **MontuckyMadman** » Wed Dec 25, 2013 12:34 pm

Hi egil welcome. You have more experience than most of us combined. Im sure we would love to here about special techniques you have learned over the years. Your fiber skis sound very expensive. Most likely overdamped by the resin and fibers but i really have no idea. I hope you contruct this beast and keep us updated.

jono · Post by **jono** » Fri Dec 27, 2013 11:10 am

Egil,
i like your idea. I am wondering if using only carbon and resin with a flax core will lead to a less lively ski?
I could see reversing the normal method of construction with a composite core and veneer top and bottom layers. You would end up with a super thin ski. Maybe the thickness/type of the veneer layers would determine liveliness?
Maybe a 1.6mm veneer core with built up carbon layers for targeted stiffness?
Maybe the carbon/flax system is lively enough? I am curious.
With such a thin core do you think inserts will be enough? have you given any thought to incorporating your binding base plates into the ski during layup?
jon

skidesmond · Post by **skidesmond** » Fri Dec 27, 2013 1:22 pm

Looking forward to hearing more about this build. But I have the same concerns about thickness for mounting bindings. What weight of CF are you planning on using? I made a test sample using 2 layers of 9.4 oz Uni CF and 3mm poplar. If was very very stiff. I can't imagine 12 layers of 9.4 oz Uni carbon bending much. Sounds like a cool build though. Can't wait to hear more.

Jibber · Post by **Jibber** » Sat Dec 28, 2013 9:49 am

I wanted to try resin infusion but there is no way to get resin between VDS and edge. Would be interested in your approach regarding this challenge...

Cheers, Christoph

SleepingAwake · Post by **SleepingAwake** » Sat Dec 28, 2013 10:32 am

Jibber wrote:I wanted to try resin infusion but there is no way to get resin between VDS and edge. Would be interested in your approach regarding this challenge...

Cheers, Christoph

I guess it would work with a very light fiberglass mat (like 30gsm or so) between the edges and the ruber. And put the ruber just on the edge, but not any further so it doesn't seal the gaps between the teeth...

MontuckyMadman · Post by **MontuckyMadman** » Sat Dec 28, 2013 11:27 am

Even without vds u really thik the resin will go into those tooth gaps? Its like the perfect airtrap. Depends on the viscosity i guess. Seems hard to get it all in there even with my fingers.

SleepingAwake · Post by **SleepingAwake** » Sun Dec 29, 2013 2:47 am

MontuckyMadman wrote:Even without vds u really thik the resin will go into those tooth gaps? Its like the perfect airtrap. Depends on the viscosity i guess. Seems hard to get it all in there even with my fingers.

that shouldn't be an issue, because at first there is a vacuum there and resin will be sucked into it.

Egil · Post by **Egil** » Sun Dec 29, 2013 7:02 am

I'm going to use a VDS with one layer of flossed glass on one side hopefully this works. If not I'll just build without VDS, I'm not so sure it is needed as the flax will dampen the vibrations and there will not be as much tension from mismatched thermal expansion as I will cure at room temp instead of the 120 deg C I'm used to.

About liveliness I'll just have to try.. if its to dead I might add some metal for more pop.

I'll also build one with a bamboo core for reference.

The core will cost a lot compared to a normal so I guess it can't be built commercially but this is for fun

I'll start a build thread as soon as I get the flax, hopefully next week but there are a lot of bank holidays now so we'll just have to see.

I have thought about incorporating the binding in to the ski but not at first. As I'm a monoskier i don't need safety bindings so this should be quite easy.

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Solid fibre core

Solid fibre core