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Back assembly on a clasical
http://mowrystrings.luthiersforum.com/forum/viewtopic.php?f=10102&t=13224		 Page 1 of 1
Author:  Mike Manuele [ Wed Aug 15, 2007 3:49 am ]
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While I was waiting on rosette materials and other wood for a classical I'm building, I got excited and after joining the back I decided to brace it as well. A few days later I read the sentence in the Courtnall book that says I should wait until the back is ready for assembly before gluing on the braces so that it retains its shape.


So far the back looks ok (it's been weeks), should I leave it alone or would it be best to shave off the braces and wait until the back is ready to be assembled before gluing on new ones?
Author:  Michael Dale Payne [ Wed Aug 15, 2007 4:25 am ]
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How did you form radius of the braces? How stiff are the braces? Did you glue them using a radius bowl for support during glue up?

My guess there is no need to re do the braces. Check the back with a radius gauge. if unhappy then do it again but I doubt you have issues.
Author:  Mike Manuele [ Wed Aug 15, 2007 4:45 am ]
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[QUOTE=MichaelP]How did you form radius of the braces? How stiff are the braces? Did you glue them using a radius bowl for support during glue up? QUOTE]


I used mahagony for the back braces, marked the radius with the same template I used to make my radius dish, and I formed the radius of the braces by planing them. I glued up the baces in my go-bar deck using the radius dish. The braces seem plenty stiff, and the back appears to be holding its shape well so far, but it's going to be many weeks before I can glue it up.
Author:  Alexandru Marian [ Wed Aug 15, 2007 4:51 am ]
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You should be fine if your humidity levels don't move a lot. 
Author:  JohnAbercrombie [ Wed Aug 15, 2007 6:50 am ]
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You can just park the back in the go-bar deck when it's not being used for bracing the top, etc..
If you leave the back hanging up, you will definitely notice if you have a problem- I had a flat-sawn back move so much it 'turned inside out' in spite of being (very lightly) braced. Now, that's when you have to take off the braces, get the humidity under control and start again...(as I did).
You should be fine as long as the humidity doesn't change a lot.

Cheers
John
Author:  Alan Carruth [ Wed Aug 15, 2007 9:20 am ]
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As has been suggested, the main problem is if there is a humidity change between the time you glue on the braces and the time you close the box. I would say, though, that almost any amount of humidity change can be a problem; certainly I would not want it to change by more than 10%, and would not be surprised to see problems from a 5% change.
Author:  Mike Manuele [ Thu Aug 16, 2007 1:31 am ]
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The humidity has risen in my work area just about 10% since I glued up the back. I took it out last night and it looks ok - I checked it against a long concave radiused sanding block and it still conforms to the curve.


Also, can I assume that all should be well if:


-The back still conforms to the correct shape
-Before closing the box, I bring the shop's humidity level back to where it was when I glued up the back


 
Author:  Alan Carruth [ Thu Aug 16, 2007 7:01 am ]
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Actually, come to think of it, Indian rosewood is one of the most stable of all woods, with far less expansion across the grain than most top woods. You can get away with more humidity change with it. Still and all.....
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