Official Luthiers Forum!

Hi!

I'm currently building my second guitar, and for this one, I'm taking the time to build nice and clean molds, templates, jigs, etc... I'm also taking the time to take the weight, density and deflection rate of important pieces, like the top, the braces and the bridge.

I've build a jigs to test the combinated flexion of the top. It clamps the perimeter of the top to the right shape, over my outside mold, and there's a traverse that hold my caliper right over the bridge location.

All that missing is the weight, and there are my questions.
How much? 200g, 500g?
Is it relevant to take data from different weights?

Also, I would like to know where I could find precision gram weights?

Thanks a lot
Francis

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Francis Richer, Montréal
Les Guitares F&M Guitars

Francis,

I don't have a clue about doing deflection tests.

I do remember seeing calibration weights when I bought a digital scale for mixing hide glue.

http://www.oldwillknottscales.com/scale ... ories.aspx

Hope this is of use,

Mark

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A world without music would Bb.

Thanks for the help Mark, but it looks like they don't ship outside US.
In fact, I'm looking for a place I could walk in and buy it, instead of paying high shipping rate cause of the weight.

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Francis Richer, Montréal
Les Guitares F&M Guitars

Francis, it's much cheaper to weigh an unclaibrated weight on a gram scale to get an accurate weight, than buying calibrated weights. I buy the lighter exercise weights and just weigh them. The only caveat here is having access to a gram scale with the range you need.

The amount of weight will depend on your wood size and span, for example I use 16 lbs for brace stock that .32 wide X .75 tall, over a simply supported 12 inch span. But only use 2 1/2 lbs on a completed top.

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Jim Watts
http://jameswattsguitars.com

A nice simple method that Trevor Gore mentions in his book is based on the idea that the top on a highly responsive guitar will have a stiffness that results in around a 2 degree rotation of the bridge under string load. Easy to measure. Place a ruler with its centre over the bridge and stick it down with a hunk of blu-tak. Measure the distance between each end and the soundboard. Relax the strings and measure again. Using some easy math, caculate the angle of rotation of the bridge to determine whether your top is at a stiffness that maximises performance. Or measure a guitar you like and aim for that value.
Cheers
Dominic

Francis: I don't think most folks clamp the perimeter of their samples when doing deflection testing. We may want to consider that for comparison to other folks results. But I may have misunderstood your statement.
Tom

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A person who has never made a mistake has never made anything!!!

I don't believe there are any real standards for this. The important thing is to develop a system that you can perform repeatably and accurately. I use a brick setting on a 3" square cork lined block for my test weight. It weighs 2556 grams all together. I use that same weight for the plate alone as well as the braced top.

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Brian

You never know what you are capable of until you actually try.

https://www.howardguitarsdelaware.com/

My results are for my information, I don't want to do comparison with other people but with my own work. Just to keep a regularity in my building process.

I clamp the perimeter (I put my plate on top of my outsite mold, then another piece, same dimension of the mold, come on top to clamp the plate), that way, the only part that deflects is the actual (well, future...) shape of the guitar.

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Francis Richer, Montréal
Les Guitares F&M Guitars