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wood breaking

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Paul Beeney09/10/2020 12:25:28
18 forum posts

Hi all have not built a wooden boat before i bought a model from caldercraft

called hm sherebourne now i have to bend some 0.8 3 ply wood round the outside of the deck called bulwarks i soaked the wood in hot water for 3 hours started to ease it round a jar to get the shape and the outside ply split it as not broken in two but if i carry on it will can someone give me any advice other than buy a new section from the supplier which may break again how do i bend tis without it breaking

Tanks Paul

Paul T09/10/2020 16:27:14
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7335 forum posts
1229 photos
2 articles

Hi Paul

Without being able to see it the first thought is that you are bending against the grain.

However I could be doing you an injustice so it would be easier to answer your question if we could see a photo or two.

Splitting wood has happened to all of us at one time or another.

Paul

Chris E09/10/2020 18:19:04
247 forum posts

I wouldn't just assume to buy another part as if you broke one you might well do the same with a second piece. If all else fails buy some thinner ply and laminate a part.

Punctuation & sentences make text much easier to read.

ashley needham10/10/2020 10:40:09
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7353 forum posts
156 photos

I have found that just a quick steam (over a saucepan of boiling water), or a hot air gun should be sufficient to bend 0.8mm ply over even reasonably tight curves, certainly a 500ml paint tin presents no problems with the outer grain longways. A jam jar should be ok, and I have only just recently rolled a bit around a 50mm pipe (play across outer grain) with a hot air gun.

ALSO, the curved part does not necessarily have to assume the exact desired shape if it is being glued to something else that is the final curved shape. Having a slightly curved piece may be all that’s required to lessen the pull of the ply over the shape.

Ashley

Bob Abell10/10/2020 11:40:25
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9334 forum posts
2985 photos

This is not a bad idea for tight bends

Bob

bending trick.jpg

Charles Oates10/10/2020 12:09:34
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638 forum posts
52 photos

Hi Paul, it's difficult to be sure from your post whether you are trying to bend a large piece of ply, or just a small piece to make the bulwark from. I prefer to make a template from card when I'm making bulwarks, those compound curves can be tricky. When you have an accurate pattern, use it to cut the ply to shape, making the ply ever so slightly bigger to allow for mistakes. It shouldn't be a problem to bend thin ply, provided the grain is going the correct way. If soaking doesn't do it, try steaming or heat on the wet wood, then slowly coaxing the wood to shape.

Of course, you might just have a dodgy bit of wood, but that's rare.

Chas

Kev.W10/10/2020 16:42:39
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326 forum posts
38 photos

Paul, if you are having trouble with bending plywood, try cutting the required piece from a Kellogs cereal packet (other brands available), with a good lashing of varnish or resin, this medium works very well.

Ashley has used the method with great results in the past, but is too modest to blow his own cornet wink

ashley needham10/10/2020 22:03:31
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7353 forum posts
156 photos

Yes, a good alternative method and just as durable.

Ashley

Dave Cooper 612/10/2020 11:17:24
309 forum posts
32 photos

Paul

There is a bit of a fight going on here with the wood on the inside of the bend being in compression (squeezing) and that on the outside being in tension (stretching).

Guitar makers (aka Luthiers) use something called "Kerfing". If you look on the inside of an acoustic guitar this forms the 'shelf' that the top and bottom pieces are mounted on. It consists of partially sawn through slots that allow the wood to follow quite tight curves. Bob Abell's photo gives the general idea.

With 0.8mm thickness though the cuts would have to be very shallow. I would practice getting the depth and spacing right on a piece of scrap wood first. Then try heat /steam possibly with a weight on one end to ease the ply into shape. Patience is needed with Ashley's boiling saucepan approach but it does work (at least, I've used this method with hard(ish) balsa thicker than 0.8mm.

Good luck with your project.

James Hill 512/10/2020 14:00:32
132 forum posts
94 photos

Paul,

I agree with Dave Cooper with his suggestion. It was the method I used when building my tug. I used 1/4" square stringers and on the inside of the bend I used a razor saw ( or a similar narrow blade ) and made cuts as deep as you dare go. The tighter the bend, the closer together the cuts need to be but it certainly works. once in place the glue fills the slots. I shall use the method again when the need arises. If I remember correctly, I bent mine dry, but whatever else helps is fine. Give it a go.

Best of luck,

Jim.

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