pchast wrote:Ask at a local commercial lumber supplier for bending plywood.
greygoos wrote:Dont use plywood. Use material that is meant to bend such as FRP
Woodbutcher wrote:Bending plywood has very little strength. So while it bends nicely it will not be very durable, unless you cover it with something else, which works against your weight issue. Since you already have the 1/8th inch, I would add in cross supports between your arched ribs. The more surface behind the bending piece the better. Then work slowly. I covered the front and back radius with 8.00 1/8" plywood. But I am covering the plywood with metal so I could use lots of fasteners as I went along. The glue I used was just panel adhesive. I started by stapling the edge all the way along. Use a wide crown stapler to keep the head from pulling through the wood. Some screws may be necessary also. This is where more cross bracing will help. Work slowly and steadily work forward. You can also roll the panel up slightly and put a couple band clamps on it to slowly relax the panel. Each day, just tighten the band a little. I'm sure you have noticed that when you lean wood against a wall after awhile it has a bend in it even under only it's own weight. If the fasteners showing are a problem, you can cover the finished box with Marine Vinyl material. Like a vinyl roof on a car.
Here is a about a 4" radius from a past build. It was a tight bend but it worked.
kramergwt wrote:You could woodstrip part or all of it like a kayak/canoe. There will be zero spring back to fight. If you Fiberglas it, it will be strong and beautiful.
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or $40 for baltic burch
kramergwt wrote:Try googling "strip built kayak" and check out images. I have a book that will come up in that search "The Strip Built Sea Kayak" by Nick Schade. It opens your mind to alternate construction techniques. I also think Advisory Circular 43.13 is good too, for learning. That was the FAA spec for wooden airplanes in the early years of aviation.
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tony.latham wrote:or $40 for baltic burch
Ouch. Somebody is ripping you off. I'm on the edge of nowhere, in Salmon, Idaho. It's a one-lumberyard town and three hours from the nearest box-store town. When I need 5x5 sheets of 1/8" Baltic, it's a custom order and costs $14 per sheet.
Check the price from a different supplier. 1/8" Baltic likes to bend and it's glue is waterproof. But remember, it only likes to bend in one direction.
Tony
aggie79 wrote:"Russian Birch" 3mm (1/8"), 5' x 5' ply is available near me for $19 per sheet.
I used the 3mm to skin my teardrop. The lower front radius is 6". The lower rear hatch radius is 10".
You aren't trying to to a compound bend (in more than 1 direction) are you?
drhill wrote:I think he means $40 cdn for 2 sheets. Windsor plywood has 1/8" Baltic Birch and it was $19.99 3 yrs ago. I haven't bought any since. If you look at the picture of the tongue box on my trailer, that is 1/8" baltic birch and the bend radius is 16". It was not wetted before installation and was glued in place with no fasteners as I like a clear finish.
Pretty sure he is not trying to do a compound bend, that won 't even work with paper.
dancam wrote:I have a I had originally intended to do this with pmf but changed my mind to wood so it would go quicker and be tougher against rocks.
drhill wrote:those bends don't look too tight for the 1/8" baltic birch. But it will be rather tricky to get the sides and front/top to meet in a nice even line. Somebody with some good CAD skills could pull that off.
So are you planning to cover this with canvas and paint afterward? I would think that is the best plan as that joint will be hard to do a good enough job that you would want it visible with a clear finish,
By the way, my tongue box has a clear finish but after 3 years and about 26,000 km it is showing the beating from all the sandblasting it gets behind the tow vehicle. I lightly sand and recoat it each year, but I know at some point I will be building another box. It will be exactly the same as I am happy with the size and look.
kramergwt wrote:dancam wrote:I have a I had originally intended to do this with pmf but changed my mind to wood so it would go quicker and be tougher against rocks.
Kayaks, especially sea kayaks, are made to slam into jagged rocks. The strip building process depends on Fiberglas on both sides for strength. It holds up better than aluminum and can be replaced by heating, removing, sanding and re-fiberglassing. Just info I read in that book. I want build a kayak when I finish the teardrop.
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