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O/T Shaping plywood

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  • The Artful Bodger
    replied
    Originally posted by radkins View Post
    I will take the ideas given here and go shopping for materials tomorrow, what I eventually do will be dependent more so on what I can find to do with but at least now I have a much more realistic understanding of what's involved and what I need to do it with.
    When shopping for ply I suggest you carefully study the edge to check that the outer plys are not paper thin with thicker inner plys, if so the outer plys will too easily crack and the inner plys will not bend evenly. Sometimes cheaper is better!

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  • The Artful Bodger
    replied
    Referring again to the opening post..

    Originally posted by radkins View Post
    I need to slightly bend/mold some thin plywood for an antique school desk seat and back. The back is only a few inches wide and should bend easily if I can just get it to hold that shape, the seat however will take a bit of effort to form properly but I have an idea for a method of forcing it into shape if I could just figure out now how to get it to hold that shape?

    The general principle when you have a means to force and hold the materials in the required shape is that you build a stack of thin plys, even individual veneers, with plenty of adhesive or resin between the layers then press it into the required shape and allow the adhesive to cure.

    John

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  • radkins
    replied
    Well it looks as if my original plans for making these seats was unrealistic, somehow I had mistakenly assumed that thin plywood could be formed into gentle curves but obviously it's not nearly as simple as I first thought! I will take the ideas given here and go shopping for materials tomorrow, what I eventually do will be dependent more so on what I can find to do with but at least now I have a much more realistic understanding of what's involved and what I need to do it with.

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  • Jim Williams
    replied
    The company I retired from made formed plywood parts. They laid the plys up over a form with a coating of a thermosetting adhesive between sheets. The adhesive was heated for curing by some type of induction equipment. I suggest you fabricate a form with top and bottom to hold the plys together while your adhesive sets.. You can use what you learn for future projects.

    Jim

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  • The Artful Bodger
    replied
    Quite complex shapes may be made in plywood using strips of ply laid over a former. Lay the strips close together then smother with glue and lay another layer at about 60 degrees angle and smother that with glue too. Repeat for required thickness but no less than three layers. On the final layer take a router and cut an even gap between the strips of the top layer then glue more strips in the spaces for an complete coverage of the top surface.

    I made a small car like that once and when I cut out the bonnet ( aka hood) it barely sprung at all.
    Last edited by The Artful Bodger; 03-27-2016, 05:35 AM.

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  • Mike Burch
    replied
    Originally posted by J Tiers View Post
    Check the seat back of the second one. Agree on the first.

    The second one seems to be bent back all around the periphery if you check the light and shadow in the front view. As for the amount of bend, hard to say. Not a lot, but definitely there.

    Plywood might be easier than steel, it's hard to do a "furnaced plate" in ply, but if you do it wet, well.......
    Yes. you're right! The edges do appear to be bent back a little.
    It's interesting that the sales pitch refers to the seat (and presumably the rest) being made in ash. That's reputedly a particularly elastic wood that readily takes steam bending.

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  • J Tiers
    replied
    Check the seat back of the second one. Agree on the first.

    The second one seems to be bent back all around the periphery if you check the light and shadow in the front view. As for the amount of bend, hard to say. Not a lot, but definitely there.

    Plywood might be easier than steel, it's hard to do a "furnaced plate" in ply, but if you do it wet, well.......
    Last edited by J Tiers; 03-26-2016, 10:50 PM.

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  • Mike Burch
    replied
    Thanks, J Tiers, those are lovely chairs. But if you look carefully, only the seat appears to be a compound curve, and even it is actually two simple curves at right angles. Very cunning, and beautiful.
    Boat-builders' rule of thumb is that steel plate can be persuaded to take a compound curve without heating, bashing or otherwise distorting only if the lesser curve is less than 1 in 40. Ply is similar, but perhaps a little more compliant (no pun intended!).

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  • GEP
    replied
    I have used 1/8 thick plywood, you may be able to mold it,glue it and tack it in place. I had some aggressive bends and worked perfect for me.I did 3 layers
    Last edited by GEP; 03-25-2016, 10:22 PM.

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  • J Tiers
    replied
    Originally posted by Mike Burch View Post
    Polyester layup resin is NOT a glue, though it is sometimes used as such. In a low-stress situation you'd probably get away with it.
    Laminating your own is really the easiest way to go. Whatever glue you do use, it must be gap-filling.
    There's a product called something like "Bendy Ply" which boatbuilders use for curved bits if joinery (but like any sheet material,it can be used only for simple, not compound, curvature). Three or four layers of that, glued with epoxy, will hold its curve no trouble.
    The Eames dining room chair has very significant compound curves. Presumably molded that way when being glued-up. Once you have pre-glued plywood, it is a one dimensional bending material.

    http://hivemodern.com/pages/product1...man-miller-dcw

    At least the originals seemed more compound, that one looks as if it just barely fails to be compound.

    http://mobile.designaddict.com/buy-a...-Charles-Eames
    Last edited by J Tiers; 03-25-2016, 10:10 PM.

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  • radkins
    replied
    Yes I am aware that polyester is not actually a glue but I have used it for glue and it seems to make a very strong and permanent bond, the biggest plus is that I have a gallon of it!

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  • Mike Burch
    replied
    Polyester layup resin is NOT a glue, though it is sometimes used as such. In a low-stress situation you'd probably get away with it.
    Laminating your own is really the easiest way to go. Whatever glue you do use, it must be gap-filling.
    There's a product called something like "Bendy Ply" which boatbuilders use for curved bits if joinery (but like any sheet material,it can be used only for simple, not compound, curvature). Three or four layers of that, glued with epoxy, will hold its curve no trouble.

    Leave a comment:


  • Carm
    replied
    Originally posted by CarlByrns View Post
    Resorcinol is/was the glue. It has been largely supplanted by two-part epoxy. For a small job, I would head over to a good hobby (model) store and pick up Bob Smith Industries 20 minute epoxy. It may say something else on the front of the bottle, but it will have 'BSI' printed on it somewhere. Good stuff.
    No, it was ureaformaldehyde, mixed w/water. But you bumped my memory...resorcinol is the purple stuff, two part,liquid/powder, limited creep and waterproof, long cure time.
    Glues have certainly advanced and an epoxy might be cheaper, I figured a water component would increase pliability for the OP.

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  • CarlByrns
    replied
    Originally posted by Carm View Post
    If you aren't committed to plywood, consider laying up your own. Thicker veneer stock is available, you can use whatever glue you want, but I'd suggest a two part, can't recall the name! but powder mixes w/water, has a long open time and cures waterproof. Most hardware stores carry it. Weldwood was one popular brand.
    You wouldn't have much springback and a suitable species (ash, birch, oak etc.) could be used.
    Resorcinol is/was the glue. It has been largely supplanted by two-part epoxy. For a small job, I would head over to a good hobby (model) store and pick up Bob Smith Industries 20 minute epoxy. It may say something else on the front of the bottle, but it will have 'BSI' printed on it somewhere. Good stuff.

    Leave a comment:


  • J Tiers
    replied
    There's this kind, big bend in it, but not compound.

    http://www.2ogra.com/16698-antique-school-desk-chair/

    I seem to recall another type with compound bends, so far no pic found

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