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Would you share your top mobility/deflection jig for a finished guitar; I would like to make one, and some design ideas would be helpful.

I'm wanting to measure the top deflection of finished guitar(s), strung to pitch.
Nicoletti, in his book, Mastering the Sound of the Acoustic Guitar, shows a jig on page 128 but I can't see that it would work: in spite of the little platform to place a weight, I see no way his jig incorporates a way to apply that load to the bridge).

After four guitars, I'm still struggling on how stiff/ floppy/ thick a responsive top plate needs to be. Chladni patterns and low frequency modal peaks on FFT analysis tell me I'm doing something wrong, although the sound of my guitars have surpassed my wildest expectations- there is likely some serious bias.

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Measure Twice,

Karl Borum

The photo on page 127 shows the jig in use, but now that you bring it up, I don't see how it works either. Unless the pin in the micrometer he uses runs all the way through the micrometer and the weight platform on top rests on the top end of the pin? I don't see how a micrometer like the one I have would work in that jig design.

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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

Not if this helps. But you can buy a Doug Proper Relief gage for $195 from the The Looth Group. Check out there tool page. they have some great tools. The 3D printed router is significantly better than the TJ Thomsen one.

https://store.loothgroup.com/product/pr ... ief-gauge/

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For those who don't have the book, this is the deflection jig shown on page 127:

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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

It's probably best to go to the original source of the monopole mobility concept, where you get a proper explanation of how the rig works, why it's a useful measurement to make and how to vary parameters to your liking.

Various people at various times have contributed their design ideas, with the rig I currently use shown here. Read the whole thread to see where some have gone wrong. The load is applied through the gauge's shaft.

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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

Thank you Trevor, I agree, so much that I finally just ordered the books from your link. Those books have been like the birthday pony that never came, or the Little Red Corvette one dreams about, but the time is never right to buy. Thanks too for the link to an robust discussion of different embodiments of your rig.

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Measure Twice,

Karl Borum

Ooooh SNAP!

…and well deserved. A reminder of the caliber of some of our members.


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Well, this thread showed me my ignorance of dial indicators because I learned something I didn't know about the one I have. It turns out mine (photo above) would work in a jig like the one Nicoletti shows in his book because the stem on the top of the dial housing screws off and when the tip of the plunger is depressed, the opposite end can extend up to 1" out the top of the housing. Is this a typical feature of dial indicators and that's common knowledge?

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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

Jay—

For most of the dial indicators that I own, the top is not a long housing like on yours; it is shorter, and the top of the pin has a little knurled metal cap on it. When you depress the lower part of the pin, the upper part sticks out. Take a look at images online of dial indicators, and you will see what I mean. This comes in pretty handy when you need to lift up the pin from the top to get something underneath it.

Thank you Karl! Your books are packed and will ship on Monday. Thanks again.

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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