Official Luthiers Forum!

... after jointing and thicknessing but before bracing?

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Bro. Matthew A.
Oklahoma

Mathew, I don't do flat tops myself but I remember seeing what I thought was a great video....Robbie O'briens?? - this one I think viewtopic.php?f=10101&t=18636&start=0&st=0&sk=t&sd=a&hilit=sanding that really demonstrated thickness sanding 'till you get the right "floppiness".
Other than that, search "deflection testing"......couple of recent threads.

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Dave
Milton, ON

Matthew-
You definitely want to be checking on the stiffness from the start, before you start bracing. Some wood will feel 'floppy' even in the (thick) rough-sawn form.
This is an area that I don't yet have enough experience to really 'nail'.
The best situation would be to get an experienced builder (of good-sounding guitars) to give you some hands-on advice, but this is difficult to find. (I took an expensive building course and this was one area where the teacher was extremely vague.)

If you do a search on 'deflection testing' here, you will get info on collecting stiffness data. Hopefully more expert builders will share their numbers so that amateurs will have an easier time of this (without building a whole bunch of so-so guitars).

Some folks find Left-Brain Lutherie by David Hurd, to be a useful book. (Send me a pm or email if you want to buy my copy.)

Robbie O'Brien's YouTube video on top thicknessing is at http://www.youtube.com/watch?v=JHs7s1_pbAg and it seems to have some good general guidelines. His series of 'Luthier de Jour' videos is excellent (and free).

Cheers
John

I start with stiff wood, both along and across the grain. It is pretty floppy before I brace it. My recent Adi top for an OLF SJ was near 0.080" thick. I use lattice bracing and an over sized bridge plate.

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"An adventure is only an inconvenience rightly considered. An inconvenience is an adventure wrongly considered." G. K. Chesterton.

start by just looking at the wood. thick heavy dark grain lines would usually indicate good long grain stiffness. Nice horizontal medullary rays would be a sign of good cross grain stillness and a good qrt sawn cut. I think deflection testing is the best way to go, but it takes a while to build up your database

Richard