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I saw prestresssing mentioned from DrFuzz in a previous post. Didn't want to hijack that post but want to throw out the question because It's been on my mind:

Are there inherent benefits to prestressing tops and backs? I think about how we bend sides to their final form and was wondering if there's any merit to bending tops and/or backs to their respective domes - effectively de-stressing the plates. Archtops, violins etc. are carved (unstressed), what would pros and cons be of unstressed SS tops?

The arguments Ive heard for prestressing a top are:

1. It increases strength of the top.

2. It improves the sound of the instrument. I've built both flat top and
arched top steel strings and acoustics and I must say the arched tops
always sound better than the flat tops.

I was told by Brian Burns that what Jeffrey Elliott (one of America's most highly respected classical builders) does is, after joining a top set, he lets it come to equilibrium in his climate controlled shop, and observes its arch (if any). Sometimes a top set will show an arch naturally. Elliott will use this natural arch when he braces his tops.

Now, having said that, I know that when I lay a thicknessed top down on my radius dish prior to installing the (radiused) braces, that it doesn't take any more than the very lightest pressure to push the top down so it conforms to the arch of the dish. So, I really don't think stressing is an issue. At least not for classicals, where typically a spruce top is thicknessed down to 0.085" or so. But even with classicals, some tops are thicker than others. I built one trying to adhere as closely as I could to the way Hauser built his guitars -- with tops as thick as steel string acoustics -- and getting the 0.120" thick spruce top to conform to the radius dish was equally not a problem.

So I guess I'd have to say that prestressing is not really an issue with a "flat-top" guitar (as opposed to an archtop one), based on my own observations. There's just so little stress there to begin with. The arch, such that it is, is maintained by the braces, and not really the top itself. Now, it could very well be that the arch adds to the sound, and I personally don't doubt it a bit -- but I see that as a separate issue.

Best,

Michael
Michael McBroom38885.8690740741

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Live to Play, Play to Live

I don't have a clue but... I like the sound of unstressing a top/back before assembly. It just seems to make sense to me. When it's unstressed it starts out it's life at a neutral position and that sounds good to me.

Have you giving any thought as to how to do it?

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Joe Beaver
Maker of Sawdust

I would say dont stress over prestressing your tops/backs...life has enough stress on its own

Speaking of carved backs...there have been a number of proponents over the years of carved backs for guitars, making the case that the back is a reflector of sound and that a stiffer back projects more sound.

[QUOTE=Joe Beaver] Have you giving any thought as to how to do it?[/QUOTE]

I was thinking a convex dish to match a regular concave dish and bend w/ heat/steam similar to sides.

The previous logic that tops and backs are barely stressed in the first place makes a lot of sense. The stress induced by 20 - 25' radius is negligible.

Guild had a D25 line back in the 70's in which they did press the backs.



But I have no idea what effect it would have on a spruce top or if it would even work. I would think some archtop builders would be doing this instead of carving tops if it were possible or had some merit. Who knows though, might be worth a try. Don A38887.0513425926

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Don Atwood
Arlington, VA

[QUOTE=Don A] Guild had a D25 line back in the 70's in which they did press the backs.



But I have no idea what effect it would have on a spruce top or if it would even work. I would think some archtop builders would be doing this instead of carving tops if it were possible or had some merit. Who knows though, might be worth a try. [/QUOTE]

Bill Moll makes (made?) a model with laminated top and back, just FYI. I believe it's electrified, though...

I think the stress on a beginning builder like myself is great enough while attempting to do a basic design, that somehow it translates into the tonewood. Especially when I use a framing hammer to pound in inlays and tame uncooperative bindings. This must be why I get such good timbre.
I wonder if I could use my drill press or maybe a car jack to make one of those guild backs.nickton38887.1199421296

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"Preoccupation with an effect gives it power and enhances the error"
from "Your Owner's Manual" by Burt Hotchkiss.

I have often wondered about this same subject. Guitar building is so meticulous about everything and then we go and force the top and back into position with glue and braces. I do have a Luthier made Concert Ukulele that looks like the back may have been bent. The back is pretty deep and is not a radius. I would post a photo but I’m doing some work at the house and have misplaced my camera. Anyway, this is interesting.

Philip

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aka konacat

If you think my playing is bad you should hear me sing!
Practice breeds confidence and confidence breeds competence. Unfortunately, I'm stuck in practice.

Those pressed-back Guild D-25's were ply. Interestingly, they have the reputation of sounding really good--sometimes much better than Guild's higher-end models. That would seem to bolster the "stiff back" theory. On the other hand, Richard Schneider built his classicals with redwood backs and elaborate bracing, claiming that the back is a "second soundboard."

Bruce Sexauer has built many pressed-top (not ply) archtops.