Official Luthiers Forum!

So Ed, with your set up is the deflection you usually aim for .25" ?

No, less. .200 is probably a better starting point, then assess and adjust accordingly...

12 strings often have 3/8" bracing.

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John

Went with 5/16. According to preliminary data, I should be pretty close to right on the money...I'll know more in a few weeks...

Trevor, after seeing many references to the books, I decided to do some checking. I have several books bought in the last few years, but a week ago bought your books. At the cost they are the best value for money. Now I might actually understand rather than blindly following plans. As a member of AAMIM I will be sharing my find at the next meeting.

They're awesome!

Thanks, Ed!

Thanks, Mike! Make sure you take yours home with you !

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Trevor Gore, Luthier. Australian hand made acoustic guitars, classical guitars; custom guitar design and build; guitar design instruction.

http://www.goreguitars.com.au

The deflection will be linear up to a point, then it will become non-linear. You passed the point of linearity in your test. Try 1 lb, then 2, then 3, etc. Plot it out. Back in my college days, this was covered under something called "Strength of Materials".

Mike

I'm sure you're right about linearity at small deflections. From what I've read, it seems that the weights people use for this are in the neighborhood of five pounds. I didn't want to double that to ten pounds because I expected it would give very non-linear results. I chose those weights to bracket five pounds. It would be interesting to know at about what amount of deflection the transition to non-linearity occurs with a setup like Ed's. It seems there would be a sweet spot where the deflections would be in the linear range and be big enough to measure accurately.

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Once in a while you get shown the light in the strangest of places if you look at it right - Robert Hunter

If you really want to warp your head... we can go back to the discussion of Go-Bars and maximum normal force (turns out for a 1/4" fiberglass Go-Bar, you get about 7 pounds of normal force no matter how much deflection)

I actually understand that.

What I don't understand is why they are called Go-Bars.

Mike

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Steve Smith
"Music is what feelings sound like"

Because they go flying past your head if you aren't careful?

Alex

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"Indecision is the key to flexibility" .... Bumper sticker

One of the advantages of using a tap method (dynamic vs. static) to work out the stiffness (Young's modulus) is that you don't get excessive deflections. I find it's quicker, too. It relies on having rectangular, flat wood of uniform thickness, same as deflection (static) methods.

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Trevor Gore, Luthier. Australian hand made acoustic guitars, classical guitars; custom guitar design and build; guitar design instruction.

http://www.goreguitars.com.au