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Discussion in 'Luthier's Corner' started by rgarcia26, Jul 20, 2012.
Have anyone here have experience bending plywood for the sides of an Semi-hollow BG 335 Gibson style
If I'm not mistaken, it requires heat and steam to do it properly.
You can make a steamer out of pvc pipe, I've seen it on This Old House, very cool if you bend a lot of wood.
I've used PVC pipe held vertically, towels to seal the top and around the kettle spout, and a steaming kettle at the bottom end of the pipe to bend solid ash struts 1/2" thick. It works well.
Would ply not delaminate with steam?
Umm... There is such a thing as "bendable plywood" , but in my experience it has been thicker than guitar-body stock, and used for curved case work. I've used it in my day job to create curvred forms for modern-looking returns in euro-style cabinetry and bookcases. I think laminated guitars, drum shells, Kay Basses, etc. are made by heating/steaming individual laminates and then gluing them together in a form. In fact, I think the heat part is often skipped based on the type of wood, thickness of the laminate, etc. So, for a hollow-body instrument, you're either going to make forms, or bend strips of solid stock, which is where the steamer comes in. Probably both. I'll let the actual luthiers take over here.
People do this all the time for homebuilt aircraft. The leading edges on a lot of Pitts are 4mm plywood which can be bent to a radius as small as 1.2''. Google "bending aircraft plywood"
While there is bendable plywood, why use that instead of solid wood? Its going to look better and sound better. The price probably isn't too different either.
The old school acoustic guitar builders use a bending iron to bend solid wood for sides. The simple version is a steel pipe capped on one end with a torch or burner set blowing into the back to heat the pipe. The wood is then worked over the pipe and the heat allows the board to be bent to shape. LMI sells a very nive electric bending iron as well. Water can be applied to reduce burning or scorching depending in the wood species. I would reccomend against steam bending for parts used in instruments. Steam introduces a good bit of moisture back into the wood and ultimately it's the heat, not the water, that loosens the wood fibers and allows them to be manipulated.
....and after those fibers have been manipulated, they then hold they're shape, to some extent. Same with flitches which are adhered in a mold. If something is manufactured to be flexible, what are YOU going to do to make it stiff? I guess the real question is; is the minimal amount of glue + kerfed edge bracing enough to keep everything together, when the sides are not contributing anything structurally? When you make a plane, you don't remove the mold before flying! That's why luthiery is different...
Thats a good point about the inherent weakness of a material meant to flex and bend. You'll need to laminate at least 2 layers of material to create rigidity.
I didn't know that u bend ply using PVC pipes, I though that the traditional, hot pipe will do,
I seem bendable plywood on the net of 1/8" thick that's just about the right thickness, I am deviating on using traditional wood or ply, the good about ply is that it comes in sheets of 4x8 that give me room to try few times, this is my first time and I know the horns got a extreme bend.
Or, thinking of it the opposite way, you need to divide the ridgid, curved, end result into layers to create flexibility, if you want to laminate. Again, Ive done this with curved casework (crown and baseboard moldings), but I'm no luthier. The last time I did this was several years ago. I laminated thin strips of wood onto a mold, and ran them through a W+H shaper to achieve the profile. The wood was cypress, my thickness was probably 1/16 for each layer (full width,3-4"), my radius was at least 30", and no heat was required. I don't remember what my adhesive was, probably titebond II. I sure miss doing that kind of work. Dang this economy!
Edit: the OP came back! The PVC is just used to create a vessel for steaming, not as a "hot pipe" for bending.
If the ply is "bendable", that means you dont need heat, or anything else to bend it- that's the point! There's no "trying" anything involved. You adhere it to something that gives it a final shape, and that's it. But without being adhered to something structually superior, it won't keep it's shape! The laminated sides of a guitar keep their shape, roughly, as does the steam bent sides of your DB. The light construction methods, which are deemed necessary for tone production and light weight (and ultimately, playability) demand this. So... how exactly are you going from flimsy sheet goods/raw material to > gig worthy final product? What is the build process? I don't understand.
This is exactly correct. I would be hesitant to reinvent the wheel here. I would have a real concern about delamination. Call LMI or any of the other wood suppliers and ask for orphan sides. You can often get sides that don't have a match very cheap. These are great for practice or painted bodies. Check ebay for a hot pipe or look into plans for a "fox bender" if you plan to do more than a couple of these the bender is the way to go. With a pipe patience is the key.
Here are a couple of pictures of my homemade Fox type bender. Cost on this was about $40 and I will do a couple of things differently next time, but this one is completely functional. For heat I've used a silicon heat blanket $$ (google), but you can use lightbulbs as well.
I've bent 7-ply 3mm birch plywood many times. No problem with delamination and it stays on the bent shape great. Only little water from spray bottle is needed. I use copper pipe and heat gun as bending iron. Very easy after some practice.
Okay, this makes sense, but is this material marketed as " bendable plywood"? Or is it a stiff sheet good that you are using traditional lutherie techniques to form? Seven plies in 3mm- wow!
Guys, the thread title clearly says "blendable" plywood. He's obviously trying to blend the plywood with some other beautiful hardwood to make it look nicer. Get it right!