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I have a vacuum press & would like to do my bracing with it, but suspect i need to use less clamping strength, HG. Does anyone know how much I can use without crushing the spruce?
Mike McNerney, ottawa

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Mike McNerney

Mike, you won't crush the spruce. There will only be 12 - 14 psi available, which means that a 1/4" X 12" brace will only be bearing 40#, more or less. Good luck getting the brace positioned and the vacuum drawn before the hhg chills. I'm not saying you can't, but I think it might be a near thing, even gluing one brace at a time.

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Dan
http://www.acme-archtops.com

What Dan said on the pressure, it's PSI you should look at rather than overall pressure. Vacuum puts out absolutely minuscule PSI compared to a conventional clamp, but it adds up over surface area.

As for the speed thing, that's all a matter of the person operating it and how much CFM your vacuum system has. If you work fast and/or use a template to line up the braces it's quite doable even all at once. Unless you're in production and need to be super fast, though, I'd put 'em on in maybe two or three steps just to be safe.

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Bob Garrish
Former Canonized Purveyor of Fine CNC Luthier Services

I'm thinking on making a template out of 1/4 white masonite similar to those plexi ones you can buy & keeping all in the rectangular shape & hot melt glue the temp to spruce then drop the braces in, maybe even put a lite coat of finish on the rest of it first though that may add to the work?
mike mcnerney

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Mike McNerney

UHMW is a better choice so that you dont have to worry with any glue adhision issues.

MichaelP
Sorry, could you spell out what UHMW is & availability?
thanks
MM

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Mike McNerney

ultra-high molecular weight, I think, a dense and slippery plastic with no pores to speak of for the hide glue to grip (although hhg can get a death grip on glass). If you could manage really smooth and polished cutouts in a plex template, and then paste-wax them, that might work, not to mention carefully limiting squeeze-out, otherwise you might be pioneering the spruceplex composite top.

Might be simpler to lay out the centerlines and length limits in pencil, and then tack the braces down with masking tape so they won't skid around as the press membrane sucks in.

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Dan
http://www.acme-archtops.com

Yea what Michael and Dan said on material to use. I particularly do them for the finger braces and tone bars. I for the most part do the bridge plate first, then the upper transverse brace. I then fit the X to bridge plate and do the X, finger braces and tone bars in the vacuum clamp at one time. I don't use HHG, so not a time issue, but don't want to drink a cup of coffee either when applying the glue and then setting the braces. I do the vacuum for about 10 minutes or so, then when glue is kind of leathery (for lack better term which I am sure there is one) I clean up most of the squeeze out and then reset the vacuum for another few minutes. Take out and clean up and whittle it down. Would note for most part my braces are already shaped to whatever I am doing IE: scallop or non-scallop, so mostly just voicing process. Oh yea the little X cap at same time. If use something the glue can stick to, it will and then have a mess.