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Guitar Tops - Longitudinal Stiffness vs. Radius
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Author:  Chris aka Sniggly [ Thu Jan 21, 2010 11:31 pm ]
Post subject:  Guitar Tops - Longitudinal Stiffness vs. Radius
This subject has been on my mind for a couple weeks now.

When we radius (or dish) the side assembly, is it not correct to assume the following?

1.) We are 'loading' the top? Meaning that when we glue the top on aren't we placing it into a forced and permanent state of flex?

2.) If that holds true, then the shorter radius would induce a greater 'load'? For example: A top attached to a side assembly that has been radiused to 25' would experience a greater 'load' than a top attached to a side assembly that has been radiused to 50' or 60'?

3.) So then....could you load a top too much with too short a radius?...... and would a longer radius benefit the guitar (within reason) as a whole...allowing the top to move more efficiently?

As a general rule isn't spruce stiffer on the longitude? Every one I've done seems that way.

This all comes from a sense that along the grain stiffness is something I haven't been paying enough attention to. I'm not an engineer folks...no way...but I think too much fer sure.

Any thoughts?
Author:  Michael Dale Payne [ Fri Jan 22, 2010 8:58 am ]
Post subject:  Re: Guitar Tops - Longitudinal Stiffness vs. Radius
You need to think of the top plates like the stressed aluminum skin on an air craft and the bracing like the frame it is attached to. While true that the skin has been forced or formed around the braces the braces are in their neutral state until when glued to the rim. This means that the skin nor the bracing structure is seeing no added load at this point. At this point in time you have a stressed skin dome construction. The dome is not loaded in any way until we ad string tension. The skin has bee shaped using it normal flexibility cross grain and a tad of preload in the long grain but really very little.
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