My first plywood kiteboards

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My first plywood kiteboards

mikeli
After a lot of reading on the forums I decided to make myself my first light wind plywood board. I decided to do some kind of copy of Spleen door, mostly because of its cool shape that I really like.
I used poplar plywood (lightweight, strong, and easy to process).
Rails are made ​​of colored epoxy resin. I really have hard time to pour out the channel for railse, due to leakage of resin under the board. Holes where the fins will go are filled with resin and fiberglass cloth. Plates for the boards I cut on a CNC machine, and I'm very satisfied with how it turned out in the end.

Door 165X50


This smaller board(138X42) is created ​​from failure of the first door, due to leakage of resin from rails chanel...
138X42



Tips of the board, thinned to 2mm

Next thing I planning to do is to glue the top and bottom plate of the board in the rocker table, to get a certain amount of rocker before lamination.

I don know how to do bottom channel on the door and how hard it will be for lamination.

By the way I will use the vacuum baging technique.

Sorry for bad english.
Tes
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Re: My first plywood kiteboards

Tes
Hi Mikelli

Welcome to the forum and thanks for being the first one to start sharing their projects -- and what a awesome start! CNC cut core, your already in the semi-pro category just because of the toys you've got access to!!

They are a great looking board to. Strangely asymetrical and with the concave rails like a snowboard. In snowboards I believe the concave rails keep the rail in contact with the snow the board bends. In kiteboards, I suspect it takes some of the pressure off the rails to stop it trying to lay flat which wide boards do while killing your ankle? What do you think? ( I had to shift the footpads on my lightwind board toward the healside rail to stop the muscles on my shins hurting

I can't wait to see the board progress and get out on the water.

A couple of random thoughts: On leakage from the rails, the best approach seems to be don't rount the chanel for the rails all the way through the board. If you have a CNC you have great control over this. Leave 0.5 mm on the bottom so it forms an enclosed channel. If it does cut through to the bottom place masking tape over it and when it curing place some weights on the core so the tape is pressed flush against the table. This will stop the leaks. Also need to make sure your table is perfectly level as the cure time is long enough that it will self-level and run out the lower corner.

Also, you might already be across this but the vertical step between the upper and lower deck is a source of potential failure. You wont be able to the fibreglass to conform to such a sharp angle and this will leave the fibreglass bridging between the 2 layers. This makes it weak and prone to failure. I hve even found that 45 step with woven fibreglass is still a sharp but might be ok if you're using twill or stitched unidirectional. One of the sources of problem is that the vacuum bag sometimes does stretch enough either so the glass there never gets squeezed down. Best approach is either to use epoxy mixed with lots of q-cell or microballoons or cotton flox to make a thick putty to fill the join. Alternatively you can use a router to bevel the edges or good old sand paper and hard work.

Channels on the underside are tricky. I've thought about this for a while now and haven't cracked it.

The first question to ask yourself is whether its going to improve the ride significantly over maybe adjusting the fin size? I suspect there will be some trial and error to get it right so you need to be sure the effort is worth it.

Some ideas I've been playing with are to use two vacuum bags. The first one goes over the entire board so that it will stretch over the 3D contours top and bottom.Pull a partial vaccum on it so that you can remove wrinkels and hold everything in place. Then put the bagged board on the rocker table and place it under a vacuum bag to get it to conform to the rocker table. As an alternative you coulduse the full bag and rather than using vacuum film to bend it over the rocker table use a sheet of perspex of 5mm or so mdf placed over the top and then clamped down. This might only be practical if your rocker table has jigs at the side that close from the top and bottom or you can put a cat track over it.

Two other more out there ideas are to create the rocker table upside down and vacuum the lower part of the core with the channels facing up. Then after that is cured then use the normal rocker table and stick the top deck on and lay it up normally on the top. The second is to carve the channels and make a mold of it out of rubber, for example 2 part silicone rubber or similar that you can but at a shop that sells mould making supplies (for casting etc). There might be other material you could use instead of 2 part silicone. Maybe one part like you use for waterproofin windows might be enough for small channels. Maybe you could do something with cheap polyester resin and fibreglass. With the mold piece you could place them on the rocker table under where the channels will go and then lay it up normally.

Hope this helps an we're looking forward to see how things progress.!!


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Re: My first plywood kiteboards

mikeli
Hi Tes

Thank you so much for your advice.

As for concave outline, I do expect that this will reduce the pressure that board create trying to go flat, but just in case I moved inserts more to heelside.(In a photo maybe does not look like it, but it is).

Rails channel problem  I solved  with double adhesive tape, but be very careful not to choose too strong tape.

You gave me a lot to think about bottom channel, most interesting sounds reverse rocker, I think I will try that first. I'd like to do channel because it aloud me also to lose a few more grams from the board weight. The only thing that still is unclear to mi is how deep channel should be? I was thinking about 2 mm.

Edges on the top plate should be bring down  at 45 degrees  I will use thre layers of 160gr twil fiberglass cloth.

I will continue with the project in a few days. I'll keep you informed.
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Re: My first plywood kiteboards

downunder
Hi,

not bad looking board! Congrats!

I think you need a bit more than 45 degrees, something like 30 would be sooo much nice to see!

And not only for a nicer look, but 45 is still a bit to much for 160gr fiberglass to nicely bend (as Tim mentioned). So you might end up by having to much epoxy or uneven fiberglass all around. With 30 degrees this didn't happen on my board, it's smooth bridging, very, very nice.
And mind you, my vacuum bag at that time was 1mm vinyl ! And still confirmed nice with 30 degrees angle!

The rails for me were never a problem since I route a channel at bottom (this is where I ruin my rails anyway), and leave just 1-1.5mm all around so the epoxy can go in nicely. And W. System is pouring really well into the channel. After all finished I take the wood edge on top at about 45 degrees and varnish everything.


Good luck.

Drazen
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Re: My first plywood kiteboards

mikeli
I did a little test. I made a miniature board with the same material as the real one, I even poured the epoxy in the rails. The goal was to see how much of rocker will stay after gluing two layers of board in vacuum on rocker table.

I was surprised that after removing "board" from the rocker table, rocker of board was not reduced at all. Even so it remained such after two days.

It encourages me because I think I will have no problem with springback after glassing.










Thanks Drazene for your comments. I will listen to you, I'm going on 30 degrees.

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Re: My first plywood kiteboards

downunder
Mićko
kako ide? :) Kad cemo na Bol?

good to see some tests before the real thing!  I was doing this as well and still doing it.

You are right, no problems with a rocker. It will stay like that. The challenge is to make a rocker with one piece of wood:) To make the board lighter.

D.
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Re: My first plywood kiteboards

mattma
Administrator
In reply to this post by mikeli
Great work and excellent to see the rocker stay in place!! What lay lay up are you going to use? Thinking about graphics?

Would be great to see and hear about your rocker table set up to? What is the surface material your using? What sort of pump etc. Always keen to see and hear about the workshop set up as well. Have you got your own CNC??



 

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Re: My first plywood kiteboards

mikeli
for the layup thinking to use three layers of 160gr glass on top and bottom, with carbon reinforcement under foot-straps and handle. For graphic i really need good advice. I would like pbt but it is hard to find her in Serbia and to expensive abroad. Thinking about silk and cotton. I working in printing house so i can do something with sublimation or screen printing. This is how i imagine my plyboard to look like.





Today i made inserts, they are from stainless steel A4. I really like brokite version of inserts, but cannot find abs thicker than 5mm.





Unfortunately i don't have cnc, but my friend has. Im using my other friend workshop because my wife dont have much understanding for kiting
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Re: My first plywood kiteboards

downunder
This post was updated on .
Nice work with the inserts!

It looks a bit heavy though.

Adding 6x160g will add min 480g weight (ie half) + epoxy weight + wood + steel = ?

Try going with 2x160g first. The ply will not break anyway no matter how many FG layers you put. It's the moisture that matters around the SS inserts. Carbon will not help for this as well.

For example: you will make a rocker but this SS inserts you can't bend? Even if you do, ply wood will bend all the time when riding your board, and SS inserts wont and that is a possible place for a little crack and moisture goes in...Also, wood expands and shrinks (by some %), inserts not so much.  

I think much better is to drill a 3 holes and put 3 separate inserts so everything can bend, shrink and expand. Providing your epoxy can do that as well. G/Flex will.

But I might be wrong. What others think?

PBT factory can be found in Austria, not far from you:)
http://www.isosport.com/
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Re: My first plywood kiteboards

mikeli
This post was updated on .
Drazene, hvala ti puno na savetima.

I agree, they look heavy on photo. I measure one set and they weigh about 74 gram. They are not that stiff, there is some flexibility in them. Planning to drill holes through them, then they should be lighter and more flexible.
But i agree with you about possibility of microcracks around them. Never thought of that.

Main reason am thinking using so much glass is mine inexperience with composite, everything looks so thin i easy тo break.

Thanks for info about pbt.
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Re: My first plywood kiteboards

mattma
Administrator
In reply to this post by mikeli
Hi

I tend to agree with Dean that for plywood board, especially a lightwind board you could probably get away with just 2 layers of 160gm glass with extra glass under the footpads, carbon might be more than you need.

They graphics design looks great and that's terrific that you have access to a dye sub printer. I've used dye sub printed on some type of silk/cotton maybe polyester fabric and layed it between the layers of fibreglass to protect it. It looked good. It worked well on the underside of the board as its much easier to get a smooth finish on the side that is pressed against the rocker table. If the top of your board will have peel ply etc for vac bagging then you'll need to put an other finish coat on top to make it look smooth and slick. Dean has had good results with certain varnishes ( over to you Dean) I just re-coat with resin.

There is another approach that I've seen on www.kiteforum.com where they make the topsheet separately from laying up the board. You literally lay of the player of glass with the graphics inserted and vacuum bag it on a flat surface. Then when you go to lay the board up you place the pre-cured skin on top like you would a sheet of PBT or durasurf. I've tried this myself once but I ended up with a much heavier board than I wanted because my vac pump wasn't able to squeeze enough resin out form under the pre-cured skin ( I believe that curing at elevated temperatures helps a lot here).

cheers
sam
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Re: My first plywood kiteboards

sam
with above the concave most that i hear about is maxium of 8mm but for the genral use 5mm is the go
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Re: My first plywood kiteboards

mattma
Administrator
Hi Mikelie - hows goes the board?
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Re: My first plywood kiteboards

mikeli
Hi Matt

Because of my other commitments, made a pause with the board.
But with coming weekend planning to continue. I will keep you updated, and post pictures.

cheers
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Re: My first plywood kiteboards

mikeli
This post was updated on .
Hi guys

I finally found some time to continue with the board. I decide to go first with unplanned smoler board (138X42) just in case to go somthing wrong...

 I glued top and bottom deck on the rocker table and must say that I'm very satisfied how rocker look like.







Rocker turn up exactly how I planned 3cm



I listen Drazen and Tes and do 30 degree angle on edge of top deck, looks really good.



Now when I head rocker and concave, thinking to put entire board in double side vacuum bag and do laminating without rocker table.



I forgot to mention earlier I also do little experiments with concave, so now I head 6mm concave in 2/4 of board. Is 6mm enough?



Next thing i planning is to put inserts in board...
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Re: My first plywood kiteboards

downunder
Well done Micko,

nice!

I've got a question: did you built your concave already or planning? Because you say "experiment" and not sure if is about this board or not.

6mm is plenty, it might be more on less when using it in the water

What's the weight now?

Also, this vacuum connector, what is it?

D.
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Re: My first plywood kiteboards

mikeli
This post was updated on .
I did 6mm concave on this board. I did it before rocker, with steam cleaner. Rocker I get by gluing top and bottom of board on rocker table, like i do with miniature board.

So this is how is turn up:

Is this OK?

After five days, rocker and concave not move at all, everything stay in place. I wonder if I could put board in the tube vacuum bag, end laminate everything without rocker table, since now I have desirable rocker and concave???

In this phase board is around 2200 gr, I use imprecise home body weight scale,so not too sure about weight. How much weight is OK, for the finished board this size?

Menage to reduce weight on inserts, now they are 47 grams and more flexible.


Vacuum connector I made my self, actually my friend made me from my drawings on turning lathe. It turn out just fine, just put a vacuum hose on it and it work great, with no leaking at all.



Sorry for bad english

Cheers


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Re: My first plywood kiteboards

downunder
That is good. I wouldn't steam it because you can put something (balsa) under the board when gluing two layers, and get the concave. You could do the same for the rocker:) See my last post with the carbon fiber top, rocker and concave "built in". With a vacuum that is easy...


Yes, put the board in a bag and that's it. The final weight for me is a max 2500g, but that is me:)

But, you know, the last piece is the most impressive peace of DIY equipment I've seen here! It's really nice to see what can be done with a good skill. Awesome

Now the big question: how much would this cost if you make more and sell it? I would buy straight away!

Good luck!

D.
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Re: My first plywood kiteboards

mikeli
This post was updated on .
Hi guys,

After a long time, I finally managed to continue my work on the board. I only did top, but in a few days I am planning to finish the bottom of the board. By the way, i am not sure how to do bottom...

Just both a piece of polycarbonate sheet to use as the bottom mold, because it is much stronger than the perspex. But when i do a little test something happened with surface of polycarbonate sheet, it become permanently milky from epoxy. When I use transparent UPgelcoat  on polycarb that is not happening???

Therefore whether I use polyester gelcoat compatible with epoxy, or to do complete layup with peel ply and after that do lacquering.

Here is some pictures...













Sorry for low quality pictures, from excitement i forgot to take my camera, so we used some old cell phone.
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Re: My first plywood kiteboards

downunder
Ah yes, it can be easy a loooooong time from start to the end product

But, hey, you have a great first board here! Congratulations! Very nice!

This looks like Carbon-kevlar material?

Ok, so now you want to  make a bottom layer? Why don't you just "invert" the whole poly mold (screws are already here -good job!), and do exactly the same thing for the bottom? Easy.

But:
You will need to place some balsa wood profiled to your need to keep the concave in a shape. Since you have two layers with smaller top layer.

Or:
How I do it, just place everything in one big vacuum bag...No need to do anything about the rocker and concave since it is already there. You need to be fast or plywood might get to much moisture if you just leave it for a few days or weeks (months:)

So, be fast and finish it as soon as possible...Than do the paint or whatever...

Sretno!
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