# Wooden Arch Bridge - How to make Arch?



## jimtyp (Jan 2, 2008)

I have an idea of a wooden arch bridge I'd like to make. What I'm looking for help on is how to make the wooden arch. I'm familiar with using thin layers of wood, bending them and then gluing them together. Has anyone bent a thick piece of wood into an arch? I know when they made the old wooden ships they steamed the wood so it would bend easier. Anyone tried this or have any other methods they could recommend? Would soaking the wood in water for a few days make it pliable?


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## Andre Anderson (Jan 3, 2008)

The easiest and strongest would to use several thin strips glued together over a form to make the arch. If you want to use a single piece of wood then steaming it is the only way to get it done. Soaking it in water will not soften the fibers the way the heat in steam will do. When I steam planks for my model ships I use a rube Goldberg steamer that I put together. I took a 3' or so piece of 3" plastic pipe, glued a end cap on one end and used a temporary plug on the other end, these are made to glue into the drain pipe so the system can be pressure tested to insure no leaks. I installed a wooden drawer pull so I can get it out with out struggling. At the end where the end cap is I drilled a hole just big enough for the spout on an electric steam kettle to fit into, I then built a rack to hold the tube with a slight slope towards the kettle, I put a drip can under the hole to catch the condensation from the steam. Fire off the kettle and when it is boiling put your wood in and wait about 10 to 15 minutes and check to see if it is as flexible as you need, if not let it cook a little longer and try again. This is not an exact science, each piece of wood reacts differently. Now most true wood arch bridges used a composite arched beam with several layers of 2x stock bolted together rather than one big piece of wood. It was much easier to move a whole stack of 2x12x16' long that one piece of lumber that was 12x24x 60' long and then try to bend that at the construction site.

Andre 


Edit: Jeez I reread. proof read something I write and it looks good, then I post it and then I see all of the d#@ mistakes.


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## wchasr (Jan 2, 2008)

Andre pretty much nailed the proces in a very good description. 

Chas


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## SE18 (Feb 21, 2008)

Andre, thanks for your insights. Next spring I'm actually going to do what Jim proposes (wood arch), but will be making one for concrete arch forms. I think I'll use the layer and glue method. I saw a segment of How It's Made on TV and they showed that method being used to form the curvature at the side of a piano. The jig for glueing was elaborate. 

Dave V.


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## Richard Weatherby (Jan 3, 2008)

My arches are 1/8 inch strips shot together with brads. I did not glue them in fear of affecting the stainability. Some are Trex, some are PT wood. The wood moves a lot from shrinking and swelling. I would glue it if it is wood. LOTS of CLAMPS.


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