Soundboard deflection

[Tod Gilding]

Hi
I have seen a couple of luthiers such as Somogyi useing a gauge to measure the soundboad deflection, can anyone tell me more about these gauges what they are called ? where do you get them ? and how are they used exactly.

Thanks Tod

[kiwigeo]

A dial guage would do the job. You can buy them off Ebay for nicks.

Trevor Gore and Gerard Gilet's new books cover soundboard deflection and I recall seeing their measuring jig described in one of the books.

[Tod Gilding]

Thanks Martin, I havnt seen the books yet, spending all my cash on my WAS. I will check ebay for the gauge and get those books asap

Thanks Tod

[stevevp]

There's a good article on that, here... http://www.ukuleles.com/Technology/compliance.html

[Allen]

David Hurd covers this extensively in his book Left Brain Lutherie. The above link to his web site is a bit of background on it. Based around ukuleles as that is his specialty, but the concept works for all guitar family instruments.

[Tod Gilding]

Thanks Stevevp and Allen, some interesting reading here, explains it very well.

[Taffy Evans]

Heres one of the gauges I have used for the past few years, I have another without the dial. workshop made.

[Tom West]

Dial indicators,used quite often in but not limited to machine shop work.
Tom

[simso]

Why do you want to measure deflection, the human eye is pretty good at spotting inconsistencys.

Its like the dial indicator gauges from stewmac and so forth for measuring relief on fretboards. Never have I needed to measure something that needed the accuracy that goes along with a dial indicator for a guitar. Dial indicators are for measuring 1/100 of a mm accuracy.

[Tod Gilding]

Steve, for me it's more about consistency, with different brace woods and different soundboard wood, I think you can maintain a consistency,for example I have just completed a guitar with Western red cedar top and Australian red cedar braceing and ended up nailing a great tone,my next will be a bunya top with bunya braceing,so to keep the soundboard consistant I am looking for a way to measure deflection, this could mean taking the braces and or soundboard down a little or maybe leaving a bit more, but I need something to work too to keep some sort of consistency.

Cheers Tod

[kiwigeo]

Why do you want to measure deflection, the human eye is pretty good at spotting inconsistencys.

It's not about spotting inconsistencies. Measuring deflection is a way of quantitatively evaluating the stiffness of a top. A dial gauge is an easy and convenient way of achieving same. You can use a ruler but a dial gauge is just that much quicker especially when you're doing large number of point measurements over a top. Its the same reason I use a dial thickness gauge when I'm thickness my tops.

Just because a tool is capable of accuracy to 1/100 of an inch doesn't mean you necessarily use it to that accuracy.

[simso]

Fair enough, Ive been guilty in the past of buying all the fan dangled wiz bang tools with dial indicators and so forth, got drawers full of them, but over the last ten years or so, Ive found they kind of accumulate at the bottom of the I dont use draw.
Just hate seeing money spent when its not necessary, that being said Im not infering there not necessary, but the old human eye is very un-appreciated and I think we as a society are all second guessing ourselves and not believing what we see and want additional confirmation, hence the onslaught of dial indicators for this and for that

But each to there own

[charangohabsburg]

Steve, we can't see stiffness. But we can "hear it" (tapping) which is easy if the boards are of the same size and density. Some can even feel it with their fingers. Some measure it. As you said: each to their own.

[kiwigeo]

Just hate seeing money spent when its not necessary, that being said Im not infering there not necessary, but the old human eye is very un-appreciated and I think we as a society are all second guessing ourselves and not believing what we see and want additional confirmation, hence the onslaught of dial indicators for this and for that

But each to there own

If I can buy a dial gauge on Ebay for the same price as a good quality ruler then why not go for the dial gauge?? Like I said if the dial gauge makes things easier and there's minimal extra cost then why not use it?

You mention the "old human eye being very un-appreciated". Well, my human eye is appreciated but it's also OLD which means reading 1/2mm divisions on a ruler is a challenge even with my glasses..a dial gauge is so much easier.

Cheers Martin

[Taffy Evans]

I do lots of work [repairs] on guitars with high actions , the problem is often traced to the top radius increasing or the top bellying up. I like to measure the difference between strung and unstrung, the difference can be up to 1mm or more in some cases. After the corrective surgery I can properly assess the success of my work with known facts not estimates. The customer can be advised properly of the amount of correction that was needed and not squint between my fingers as I try to show the difference in before and after. I record this on the job sheet for future reference.
Also when setting up my new guitars if I know how much the top raises under string tension it aids in the set up process when the strings are of.

As to cost and waste, not I, I use the same dial gauge on many different jigs as it uses the same method on fitting.