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Plywood has the grain running in two directions. Birch ply was the choice, I have learned, and still is. If it is 3 ply the outer two are in a single direction and the center one is 90 degrees to that. Experimental aircraft parts suppliers usually have birch. It is expensive. One trick I've used in building small boats when a compound curve is necessary, is to make light cuts on the back with a table saw. With steaming and lots of water, you can form the plywood in compound curves. The cuts on the back are later filled. Another method is cold moulding. Many wooden sailing dinghies were built this way. Basically, this means buying relatively thin veneers and glueing them over a mould. After WW2, the glue used was Resorcinal, though I don't know what would have used in period.
Erich in Seattle
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The secret to bending plywood is to start with a sheet of bendy plywood! If you go onto the Arnold Laver website there is a section 'Bendy Plywood'.
When I did the seat back in the RL I used a sheet of 4mm birch plywood. The ends were curved round and I held them in the correct shape with a couple of pieces of wood that hooked over. I then glued 1" wide strips of the same birch ply around the edges of the curved sections and clamped them on. In other words the curved edges were laminated to 12mm thick. When dry the restraining timbers were unhooked and the seat back retained its curved shape. It will spread slightly but remains flexible. This is an advantage as when you fit it back in the car it holds itself snugly in place.
Laminating layers of birch plywood is by far the easiest way for the amateur to produce a strong curved timber. Make the strips slightly oversize and when the glue has dried sand it down to the finished size. The result is very pleasing, a bit like those plywood IKEA chairs!
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I bought 'aircraft' ply 1.5mm thick from Chiltern Timber in Hemel Hempstead to make body trim panels, it's not cheap but it is quite extraordinary stuff, can cut it out with scissors and roll it up like card yet very strong and stable.
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I had some success with making curved ash pieces that are fixed to the hood frame on my Riley. The device I borrowed was simply a piece of 4" plastic sewer pipe with capped ends and a large wallpaper stripper. The piece of wood was popped in the tube and the ends capped. the wallpaper steamer turned on and the wood inserted into the pipe and I would have a cup of tea. The resulting piece of ash was then clamped to a former and allowed to cool. I was amazed how effective the process was, even for a rank amateur as myself... As Charles said, you do have to work quite quickly and 'over bend' a little....
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Hi. Birch ply will steam bend quite easily. Pour a kettle of boiling water over the area to be bent and then carefully bend around a former. As others have said, over bend so that when the wood is dry it springs back to the desired shape. Putting towels on the wood and soaking them with hot water helps to retain the heat.
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04-07-2020, 12:11 PM
(This post was last modified: 04-07-2020, 12:16 PM by Nick Turley.)
Although I personally am not a woodworker.
I had a new seat back for my box saloon made by my father who was a builder of boats.
He made a multi layer sandwich of ply using Cascamite glue which gives plenty of working time but once stuck is truly permanent and waterproof.
He made a wood jig on a very thick piece of wood to make the bends and clamp to. One thing of note, where it touched the jig he put polythene so it would not stick to it.
Once the whole thing was assembled he then wiped off any excess glue with a damp cloth.
It was left overnight, next day removed from the the jig, it never moved or sprung.
If I remember correctly he used 4 x 1mm Bruynzeel ply to make it with.
35 years later it is still in the car and doing good service.
Hope this is of some use .
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Whilst I have heard of IKEA, I have never been in one!
Steve's photos prove that a man can never have too many G-clamps.
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Polyurethane wood glue is the stuff for laminating. Available with either 5 or 30 minute setting time. It is moisture reactive, waterproof and expands to fill voids. I started using the 30 min but quickly moved to the 5 min as the faster setting time made jobs much quicker with less hanging about. Gorilla glue is similar but has a much longer setting time which I found a pain. All are available from Tool Station with free next day delivery if you spend over £10. I noticed Morgan using it for laminating the wheel arches of their cars on a recent TV program. Don't get it on your hands as it's very difficult to shift.
