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Pocket board building

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merl
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Re: Pocket board building

Postby merl » Sat Nov 28, 2020 12:15 am

I'm talking 75kg/m3 - at 25mm it feels really stiff so I would be scared that it would snap - I am still a bit scared to try...

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Re: Pocket board building

Postby Pierrot » Sat Nov 28, 2020 1:15 am

merl wrote:
Sat Nov 28, 2020 12:15 am
I'm talking 75kg/m3 - at 25mm it feels really stiff so I would be scared that it would snap - I am still a bit scared to try...
The foam I’m getting is 33mm and 80kg/m3 I think.
I’ll do a test to see if it snaps when I bend it. Else I’ll use the kerfing technic...

I realize using lamination on the bottom hull is easier. But my homemade rocker table is built the other way around...

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Re: Pocket board building

Postby downunder » Sat Nov 28, 2020 2:56 am

[quote=leeoo post_id=1119533 time=1606315932 user_id=99714]
Here is a short documentation of my 3rd build. First two were with foam+wood+carbon fiber, this one uses paulownia wood only.
[b]Setup:[/b]
3mm paulownia sheet (grain along board)
3mm paulownia sheet (grain perpendicular/across board)
~15mm inner 'skeleton' (2 stringers + frame)
3mm paulownia sheet (grain perpendicular/across board)
3mm paulownia sheet (grain along board)
Just for sealing i used some fine 110g/m2 glass on top&bottom.
Dimensions are ~115cm x 45cm, ~8cm rocker/nose. Weight ~2.6kg.
Unbenannt.jpg

[b]Build:[/b]
Starting with 18mm plywood board --> cut & glued together 3 sheets (54mm then) --> cut in 3mm slices.
Here are the short ones with grain across the board.
1_IMG_1818.jpg
2_IMG_1819.jpg

All sheets are glued using PU glue, pressed on a rocker table using vacuum:
3_IMG_1814.jpg
4_IMG_1815.jpg

Details of the final board before glassing & finish:
5_IMG_1871.jpg
6_IMG_1875.jpg

Finish: 2 component PU finish (2-component can) on top of glass/epoxy layer.
Final board:
7_IMG_2004_.JPG
8_IMG_2014_.JPG
9_IMG_2015_.JPG

Since I prefer riding strapless now, I attached some clear deck pads from Decathlon.
[/quote]

Excellent build, congrats.

Because u guys have Paul. wood in Bauhaus in the EU (I know, been there), the simplest build is flat board. After some time we do not need rocker for 99% of time.

Your build is nice, but quite complex, agreed.

No need for 90 degrees grain, no benefits. 3 layers of 4mm along the length made my board, stiff as rock. And lighter.

Tried it this week. Absolutely no need for bigger rocker. Or length, and Im still learning.

[attachment=0]IMG_26112020_142758_(405_x_720_pixel).jpg[/attachment]
Attachments
IMG_26112020_142758_(405_x_720_pixel).jpg

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Re: Pocket board building

Postby TomW » Sat Nov 28, 2020 1:53 pm

leeoo wrote:
Thu Nov 26, 2020 1:28 pm
Thanks thewindego and alpaia for your appreciation!

Here in Germany you can simply buy paulownia wood boards (18mm thickness, up to 600x2200mm, https://www.bauhaus.info/leimholzplatte ... p/14084273) in a local hardware store chain called 'Bauhaus'. I always asked myself why they have it in their range, as I don't know any "common" applications for this wood. It's definitely way too soft for furniture as you an apply deep scratches with your fingernails only. OK, I just noticed they also have thicker paulownia rods (45x45mm) now and advertise it as furniture corpus construction wood... so maybe it is used in furniture after all.

I agree, this building method could be scaled to surfboards also, but it's rather complex. You need a rocker table first and then you need to match the stringers (more or less) to the shape of the rocker table. That's not trivial the more 3D the whole shape gets (but of course doable). I enjoy the process of working with wood, so I didn't mind the hours... but I think you can get a decent result in less time.
So you sliced off 3mm straps from the 18mm paulonia plank and edge glued then to make the 3mm top sheet? Can you describe how you edge glued them ?

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Re: Pocket board building

Postby Breze » Sat Nov 28, 2020 2:26 pm

No, first he glued 3 sheets of 18mm together, Then he cutted 3mm slices from the 54mm block. Common method for making thin wood stripes
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leeoo
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Re: Pocket board building

Postby leeoo » Thu Dec 03, 2020 2:58 pm

downunder wrote:
Sat Nov 28, 2020 2:56 am
...
No need for 90 degrees grain, no benefits. 3 layers of 4mm along the length made my board, stiff as rock. And lighter.
That's interesting. I read from some simple Alia boards made out of a single 18mm paulownia sheet without any glass/CF layers and thinned in the center for some concave that broke along the board. And indeed, say you have an 30x30cm, 18mm thick paulownia pice. You can easily brake it along the grain with your hands only.
But probably by using multiple thin sheets even with grain in the same direction, stiffness increases as the grains still have some tilt with respect to each other.

My reasoning was to
1. have strength (along grain) in both directions
2. have this on top and on the bottom of the board
3. and I wanted to separate those strong layers away from the neutral axis to increase stiffness, like a I-beam (or H-beam).

Plus I wanted at least some volume to be able to 'sit' on the board and have some buoyancy (of course its compltely under water) when the kite ist down and you're waiting for the next gust...

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Re: Pocket board building

Postby alpaia » Fri Dec 04, 2020 8:59 am

Thanks, your technique is really interesting and should logically be beneficial as you state

- cross grain on skins like plywood so harder to puncture or split
-I/H beam effect of structure with hollow center : better stiffness to weight ratio & buoyancy
It sounds even better than the hollow wooden surf construction (plywood like skins, stringers with multiple plys)
as for alaias I also split mine in two twice kiting then I put cross-grain reinforcements. strength to weight is very poor.

This is not making a huge difference for a small & thin pocket board (having a solid wood core laminated is ok of course)
this would be a great advantage for a surf (for higher volume board the weight becomes important)
I'd be interested to see if I could build one unglassed, using a hardwood veener ourtside.

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Re: Pocket board building

Postby TomW » Sat Dec 05, 2020 1:26 pm

Breze wrote:
Sat Nov 28, 2020 2:26 pm
No, first he glued 3 sheets of 18mm together, Then he cutted 3mm slices from the 54mm block. Common method for making thin wood stripes
Av yes, makes sense. Have to get a table saw....or could i use one of those aluminum rails with a circle saw ( have one of those). My shop is getting crowded!

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Re: Pocket board building

Postby TomW » Sat Dec 05, 2020 1:45 pm

Leeoo,
Did you vbag the top layer onto the hollow board? How did you avoid top layer collapsing into the voids?

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downunder
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Re: Pocket board building

Postby downunder » Sat Dec 05, 2020 4:35 pm

leeoo wrote:
Thu Dec 03, 2020 2:58 pm
downunder wrote:
Sat Nov 28, 2020 2:56 am
...
No need for 90 degrees grain, no benefits. 3 layers of 4mm along the length made my board, stiff as rock. And lighter.
That's interesting. I read from some simple Alia boards made out of a single 18mm paulownia sheet without any glass/CF layers and thinned in the center for some concave that broke along the board. And indeed, say you have an 30x30cm, 18mm thick paulownia pice. You can easily brake it along the grain with your hands only.
To be fair, Im not sure that 18mm Paulownia can be broken with a bare hands only.

However, why is this relevant? People use a foam, which can be broken in any direction.

Paulownia with really fine FG, ie 80-100 grams is super strong and looks natural. It will outlast all foam builds, or even wood core builds like this one:
SAVE_20201205_232736.jpeg
Very expensive board, and yet, one single carbon layer on bottom, destined to break.

My DIY Paulownia TT is now 5 years old. Did not break yet ;) Hundreds and hundreds of hours on it:

viewtopic.php?f=107&t=2387451&hilit=My+new+year+build


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