Official Luthiers Forum!

Kyle and I are about to venture into the world of deflection testing so we can track some data across guitars we build.

We're hoping this will unlock some knowledge for us in how to thickness different soundboard varieties - not to mention how 2 tops of the same species will differ.

We'd like to see your deflection testing methods - and any input you'd like to include. Photos appreciated!

Newbie question - do you only test along the grain - or do some of you also test across the grain?

Do any of you test your soundboards after you have them braced to try to hit some goal?

Looking for anything that might help get us going down this path.

Thanks

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P A U L B U R N E R
Burner Guitars

Hi Paul, here's how we do it.
The top is suspended between two points, two fixed points.
The arm holds a dial gauge, and right beside it we set our weight.
In this case, a #4 plane--something I grabbed to use years ago, and now I've got to stick with it.
By that I mean all our tops are tested at the same dimensions, tested under the same weight, and the resulting number tells us at a glance how any top compares with all the others.

Perhaps not the best system, but it is yielding us some useful info.



Steve

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From Nacogdoches...the oldest town in Texas.

http://www.stephenkinnaird.com

Hey Steve: Show him how you and I do deflection tests on braces.....!!!
Tom

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

Ok, Tom, but are you really admitting that you're as backward as I?





The way this works is to bring all brace stock to the same dimension.
Put in the jig, and apply "One Pipe Wrench" of weight.
I usually flip 'em over and see if there's a stiffer direction, one that resists the pull a bit more.
There usually is.

Steve

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From Nacogdoches...the oldest town in Texas.

http://www.stephenkinnaird.com

Here's mine, it's pretty much a direct copy of the one David Hurd
shows on his site. Here's the url:

http://www.ukuleles.com/Technology/statmeas1.html

I've just done 2 builds since I built it, so I'm just starting
to collect data. It's a simple softwood frame standing on 4 1" dia. PVC
pipe legs. The legs are attached to the frame with 1" pipe straps. I
notched the frame for two support bars so that I can vary the distance
between them to work with larger or smaller test samples. I'm using a
2' length of iron pipe, weights about 1600 grams, for my load. The load
should as wide or wider than the sample so you are applying the force
evenly across the width. I bought a digital dial indicator on sale at Harbor
Freight for $15, normally it's about $30. You can also use a mechanical
dial indicator ($12). The advantage of the digital indicator is that you want
some deflection on the guage before you load the sample. With the digital
gauge, you can zero that deflection out, and measure your sample deflection
directly- saves one subtraction step. I also use the Excel spreadsheet on
David's website (PlateExStatCalc.xls) to calculate the specimen properties.
You just modify it for the dimensions between supports, load, and specimen
size to fit your setup.

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Gene

Politicians and diapers must be changed often, and for the same reason- Mark Twain

Here's mine for tops, I get both directions form one jig. I place a weight on top of the platform.

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Jim Watts
http://jameswattsguitars.com

Here is mine
5# weight
Only test longitudinally
Not a good photo but I can take some more

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Andy Z.
http://www.lazydogguitars.com

Andy, that setup is sweet!
David Hurd had a pretty good write-up in 4 parts in the Tutorials section - here is part 1:
http://www.luthiersforum.com/forum/viewtopic.php?f=10117&t=24469

Check out chris paulicks youtube vid

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Formerly JJH

I learn more from my mistakes than my successes

OK, since you asked.

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I didn't mean to say it, but I meant what I said.
http://www.brackettinstruments.com/

Steve: I,ve got the market captured on backward. But than again it saves on tools if they serve a duel purpose......!! Besides that my plumbing days are behind me.Take care my friend.All the best of the season to you and yours.
Tom

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

Woody, I like your set up, I suppose you could even do deflection testing after braced?

Chuck

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That's just something build for a quick set point. One of these days I be making one simular to the one in" Left Brained Luthier" .