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 Post subject: Re: balsa or any super light plywood ?
PostPosted: Sat May 25, 2013 2:37 am 
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Location: Traverse City, MI usa
Find one of those cheap used hollow birch doors, take apart and you'll have 2 good pieces of 3mm ply. Glass stringers in the middle, does change the flex pattern of the board when Sandwiched in between the 2 pieces of Ply, remember the plywood grains are at 180 deg from each other.
Hell if your using epoxy to glue the ply together, mite as well throw some glass in.
In the past The very few boards I have broke were ones that had large voids of glue, so now I screw middle half way and outside, I also get a shit load of more excess epoxy out.
Go THIN use some glass in the middle, it add another layer in the mix, if to much flex put some glass on top.


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 Post subject: Re: balsa or any super light plywood ?
PostPosted: Sat May 25, 2013 3:14 am 
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but be careful you don't get a door with skins that have one layer of clear veneer on top of pulp/mush. Those would not cut it.


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 Post subject: Re: balsa or any super light plywood ?
PostPosted: Sat May 25, 2013 3:42 am 
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Joined: Mon Jul 26, 2004 6:50 pm
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Location: Wolfe Island Canada
Why not just get a foam core like corecell? I have never tried paulonia and cannot surce it here in Canada. I did some balsa boards and that was ok but shaping corecell compared to a random wood grain is so much more consistent. I don't believe you can make a board as light with wood either and the springback issue is a major pita.


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 Post subject: Re: balsa or any super light plywood ?
PostPosted: Sat May 25, 2013 1:09 pm 
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Location: rhode island
I'm not sure i completely agree with everything Stan has said, but he is always the voice of reason.

I do agree that there is no reason to avoid foam cores just because you dont have a vacuum pump.

must be a few million surfboards made from clark foam long before anyone thought of vacuum bagging,

-bill


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 Post subject: Re: balsa or any super light plywood ?
PostPosted: Sat May 25, 2013 6:51 pm 
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avoiding foam cause : dont have vac pump : divynicell is a PITA to sand, and is very expensive, so, shapind a BIG bloc of corecell or any foam IS : HARD to get nice shape, expensive, pita.

scewing a foam board on the rocker table does not work, it's foam.

i have a core shaped and railed ready do do, but cant get a pump, so, while waiting, playing around with wood.

wood is cheap, easy to grind down with power tools, easy to scew on table, glue it with wood glue ( just use the water tight stuff ) and does need only one layer of glass ( cheaper ).

the spring back was not an issue, had moderate one on the rocker and quite non on the concave ( will send some pics soon, actually, i heard so mutch about the spring back that i put a lot off rocker in the board and, had to mutch rocker when taken out the scews, even after grinding a lot of material down, witch lowers the rocker a bit, had to mutch i had to put 60 kg on the center of the board after laying the glass on the bottom to lower the rocker.

an other reason for wood board : the low price let,s me try shapes that i can after reproduce with foam and carbon if i like them.

finished board will be : 30 dollars for the wood, 5 dollars glue, 1 dollars inserts, 25 dollars epoxy, 4 dollars filler, 20 dollars glass. oh, and let's say 15 dollars of sanding discs/betls/papers.

around 100 finished for a door.


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 Post subject: Re: balsa or any super light plywood ?
PostPosted: Sun May 26, 2013 12:44 am 
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You could screw a foam layup down using ply on top to squeeze epoxy off, but you will have a shit load of holes to fill, and pressure would be uneven. If your cheap, just use a shopvac on your Vac Table, If you get -1 PSI thats like 250kg or so sitting ontop your board.


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 Post subject: Re: balsa or any super light plywood ?
PostPosted: Sun May 26, 2013 6:10 am 
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Location: Wolfe Island Canada
OK.

In Canada corecel is cheaper than beer.

Second I did several cedar core boards and they were waaaaay heavy......:(

My standard shape 135x40cm corcel bomber production is 2kg or less and no way will break for years.

Wood likes to suck water as well...LOL

Stan


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 Post subject: Re: balsa or any super light plywood ?
PostPosted: Sun May 26, 2013 3:35 pm 
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well, i know they going to be less efficient then commercial ones, heavyer, more expensive then used ones, and take a lot off time, but, i cant wait to try mine on the water, try the shape i imagined, try riding something i did myself ! tha's the trill.


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 Post subject: Re: balsa or any super light plywood ?
PostPosted: Mon May 27, 2013 3:05 am 
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Several years ago, i was building boards with 3 layers of 3mm baltic birch plywood. I sold a few of these boards under the "Anomaly" brand.

The boards had around 2.5-3 cm rocker and about 4-6mm concave if i recall correctly. I used to have a bunch of pictures in the gallery section here but that section seems to have disappeared?

I used a vacuum bag and clamps to laminate 3 boards at a time but if you are patient and use slower epoxy you can just use screws and/or clamps to get a reasonably good laminate. To get the concave you just run a lattice strip down the center of the rocker table and then clamp or screw down around the edges.

If you use screws to clamp the edges then you can just make the "blank" wider and with more concave than you want and then cut the screw holes out when you shape the outline.

The lattice strip is approximately the thickness of the concave you want in the resulting board.

The forced compound-curves in the wood help get even clamping but with a vacuum it does work better/ easier.

Initially I was glassing these boards but eventually I realized that with the birch plywood the concave added enough stiffness so that the boards rode well and lasted a long time with just an epoxy coating to keep the water out.

Depending on the size, the wood boards weighed 1-3 pounds more than the foam/glass/epoxy boards I also built. Heavier, but not too hard to get used to.

I think they actually rode really nice: slightly softer flex, but with a really good spring-back 'cause that's one of the benefits of using wood.

Trent


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 Post subject: Re: balsa or any super light plywood ?
PostPosted: Mon May 27, 2013 4:54 pm 
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A few years ago Trent? 10 yrs ago I bought one of your Foam boards!!:) Time flys when your having fun. Trent had it dailed down to 9mm, I agree with him, less and the board has too much flex, More and its a none flexable Tank.
I build my boards in the spring usually 40 degs, work time is hours with the Epoxy, no rushing, sqeezes the maximum out. New tables/jig is 5 1x4s rocker cut in, Concave I get by stepping the rocker cut at different depths, these strips are mounted to some thick ply and luan on top. so I have 5 screw points through the width, screw from midpoint to outside means max amount of Epoxy out.
Epoxy on the outside is heavy and one crack and you have water in the wood. Thats why I use a spit coat/thinned Fast dry POLY to soak into the wood followed with 6 more coats.
9mm wood boards usually weigh less than Liquid Force boards, But about kg more than other boards:)


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