Topsheet with a vac table? Can it be done?

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SleepingAwake
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Post by SleepingAwake »

in vacuum it will be super hard to get it void free. mainly there are two problems.
The first one is that the even most tiny air bubble you have trapped in there, which is so small you can't really see it, expands in the vacuum to a pretty big bubble.
The second problem is, that the resin itself will degas under a high vacuum the humidity which is trapped in the resin itself.

The first one can't be solved with wet layup, the second problem can be solved by degassing the components of your epoxy system during a couple of hours prior mixing. then mix the system and debubble the system to get rid of the bubbles you stirred in. When i need a good result this is the way I do it.

Vaccum infusion will work too. I build my kiteboards using infusion. But for a sandwich part there are a lot of subtleties and a whole lot of new things that can go wrong. but you can get a mirror finish even without any topsheet at all.
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dbabicwa
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Post by dbabicwa »

Thanks

that's actually what I've expected to hear:(

That opens a question of tiny holes drilled everywhere. I think I've posted this long time ago:


Image

The core is perforated. Why is that? Other than gluing a topsheet, there is no real reason to have it perforated....Or is it?

Ideas?
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dbabicwa
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Post by dbabicwa »

SleepingAwake wrote: Vaccum infusion will work too. I build my kiteboards using infusion. But for a sandwich part there are a lot of subtleties and a whole lot of new things that can go wrong. but you can get a mirror finish even without any topsheet at all.
Thinking about infusion as well. Duno if is possible with no too much hustle...

Yep, a shine is not the problem. Durability is ie our sand will eat epoxy in a matter of few sessions.
SleepingAwake
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Post by SleepingAwake »

Hmm, I would rather put a thin glass mat on the surface. against something abrasive like sand a gfrp has to be more robust than a simple nylon? But no experience in this direction. I never used a topsheet for my kiteboards.

The holes in the carved are because they build these planks with vacuum infusion and then you have to have those in order to get a more or less symmetric flow front above and below the core. I don't think they will help with your problem. But they certainly don't hurt either...

edit: on the carved boards there is no topsheet. and they hold up pretty well what I have seen so far...
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dbabicwa
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Post by dbabicwa »

Ah,

ok than. Wondered what for are they. Thank you.

If carved looks well than I shouldn't worry either:)
SleepingAwake
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Post by SleepingAwake »

On the other hand we don't have any shallow flatwater spots here in Switzerland... But I would give it a try.
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b2therye
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Post by b2therye »

very interested to hear more about resin infusion making boards.
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dbabicwa
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Post by dbabicwa »

Me too :)
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Post by sammer »

I don't think you can totally eliminate the tiny bubbles.
I usually put a good amount of extra epoxy on the last layer before the topsheet, then use a roller to push the excess along with the air off the sides after reaching full vacuum.
You have to have somewhere to push it to though.
Once the vacuum bag has sucked down the sides of the layup it's pretty hard to get the epoxy rolled off the sides.
I've had a bit of success using breather beside the layup with the topsheet hanging over it.
You have to have something that holds up the topsheet and stops it from pulling down tight against the sidewalls.
And somewhere for it to accumulate where it won't migrate back.
This has happened to me twice now, where I push off the excess then once the epoxy starts to get warm it flows back and creates nice lumps under the topsheet.

sam
You don't even have a legit signature, nothing to reveal who you are and what you do...

Best of luck to you. (uneva)
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dbabicwa
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Post by dbabicwa »

^
How thick is your topsheet? Is it nylon?

This one is 0.3mm I think and not nylon. I do place a 0.5mm clear plastic sheet over it to minimise a vac bag imprinting.

This makes at least 0.8mm of material (+a vac bag) to work out with the roller. Hard, hard yakka (aust. slang).

But as mentioned, a prod. board is puurfect, duno how they do it but looks great.

I did crack the PU sidewalls, if only I could get this to work...
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dbabicwa
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Post by dbabicwa »

SleepingAwake wrote:On the other hand we don't have any shallow flatwater spots here in Switzerland... But I would give it a try.
I might. Dono how to drill a zillion tiny holes without an cnc :(

Heh, but you compensate with a snow in Ch:) And cheap travel, and...Well, not with the blue sky with an orange on top. That's ours:)
SleepingAwake
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Post by SleepingAwake »

OK then, this is my setup for vacuum infusion. As i don't use any flow media yoiu can do the same thing and glue the topsheet on there in one go.

Image
infusion after some minutes. i grind some grooves in the surface of the core which allow the resin to flow. about two inches between the grooves, and they end about two inches before the rail on the side where the vacuum is pulled. holes in the core allow to get a more or less symmetric flow front. Spiral wrapping tube for the resin feed line on one side and MTI hose on the other side.
This was the first board I made using infusion and I had some little air pockets trapped on the bottom side. nothing too bad, but not perfect.


Image
and everything impregnated

Image
the concave and the rocker of the board cancel each other out in the flow direction making it planing super early for the size

Image
7mm concave

Image
UD flax just where the board is the thickest.

Image
finished board

If you wanna try infusion, make some samples with the exact same layup as you planned, same core thickness, same length as the board width, and maybe 15 cm wide. they allow you to get the process right and you can determine the perfect amount of resin you need.


cheers, Reto
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dbabicwa
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Post by dbabicwa »

Thanks for posting this.

Will need to thinker how to do just a topsheet coz I normally don't do everything in one go.

Btw what kind of fabric is the white thing?

Also, if you don't mind, why 2 inlets on the right hand side?
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b2therye
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Post by b2therye »

dbabicwa, that white fabric is fibreglass that hasn't got resin to it yet. thats mid-way through the infusion.

easycomposites.co.uk have some great videos on resin infusion if you want to have a look dbabicwa

do you recommend flow media for an infusion?

i thought the issue would be getting epoxy between the core and the base (for skis) and the edge and vds rubber would be an issue to fix.

have you done and infusion with UHMW-PE, VDS Rubber and Metal edge?
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dbabicwa
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Post by dbabicwa »

Thanks,

yes, it's a fg but what kind of like E glass, S glass, biax, triax, quad...? :)

Yeah, think of a topsheet on a kite board as a base on a skis. The infusion would be a nightmare for a snow board.

What we can't see on this photos is how the bindings inserts are made. Are they infused at the same time, premade before infusien, etc etc.

Sorry, more answers and yet more questions on a topic! :)
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