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Old 09-26-2023, 06:35 AM
Alan in VA Alan in VA is offline
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Default Glue for Press-Formed Tops

I have a fondness for clunky old Harmony and Kay archtops made with single layer tops and backs, press-formed with steam and pressure.

If I were to give that a go today, what glue is appropriate for joining top halves together prior to press-forming, without that joint going all to hell in the steamer?

It's unlikely I am going to find reasonably-priced thin sheets of spruce or birch wide enough to make a one-piece top. What's a good way to proceed? Thanks.
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Old 09-26-2023, 07:40 AM
Fathand Fathand is offline
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Have you considered joining after pressing? ╠ saw something online about making violin tops that way onše and another article about doing Selmer style tops, joined after bending. Something about support the top with the mold during the joining process. Sorry, I don't remember more.
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Old 09-26-2023, 10:31 AM
printer2 printer2 is offline
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Maybe CA? Titebond III holds up for binding bent after glue up. But that is not a high stress part, how well the glue holds after heating?
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Old 09-26-2023, 12:54 PM
Alan Carruth Alan Carruth is offline
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Making a press-formed laminated top a la the 1930s Kays takes a fair amount of technology, I think. My understanding is that they steamed the individual layers, stacked them up with glue in between and pressed them into shape over a form for the glue to dry. I'm not sure a home vacuum rig would work with veneers as thick as they used on those. Modern sliced veneers are .5mm thick, and easy to bend, but you'd need eight or ten layers to get a stiff enough top, I'd think.

A method that uses solid wood is to cut out two halves for a top that are over size, and a bit thick. These are clamped between cauls in the shape of half the rim on the inside edge. The two pieces of top wood are steamed, clamped together between the cauls, and wedges are driven in between them to force them into an arch. Once the wood had cooled and dried out the two pieces can be removed from the form and joined along the center line in the usual way. Normally they are left fairly thick, to be final carved to shape and graduated in thickness.

Viols used multi-piece bent tops several hundred years ago, and this can make a fine instrument. If what you're after is that clunky sound,that should be fairly easy to manage...
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Old 09-27-2023, 02:27 AM
Arejay Arejay is offline
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Graham McDonald's Bazouki Book used to have a chapter on created moulded soundboards for a bazouki or octave mandolin - it isn't in the latest edition but is available as a free download from his website.
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