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For anyone interested here is my latest blog post on how I deflection test my guitar sound boards. Enjoy.

http://howardguitars.blogspot.com/2016/01/deflection-testing-of-acoustic-guitar.html

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Brian

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

https://www.howardguitarsdelaware.com/

I'm unable to access your blog. Do I need to signup for it?

Thanks, Michael

I'm encountering similar.

Me too and I am definitely interested in seeing it. This is something I want to start doing.

Hmmm...... see if this works.

http://howardguitars.blogspot.com/2016/01/deflection-testing-of-acoustic-guitar.html

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Brian

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

https://www.howardguitarsdelaware.com/

Thanks Howard. Ooops- Brian
Love "the" brick.

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The name catgut is confusing. There are two explanations for the mix up.

Catgut is an abbreviation of the word cattle gut. Gut strings are made from sheep or goat intestines, in the past even from horse, mule or donkey intestines.

Otherwise it could be from the word kitgut or kitstring. Kit meant fiddle, not kitten.

There we go!

Thanks Brian

Thanks! Howard the Brick. haha

Hey Brian, I've got a brick that looks almost exactly like that one. Mine came from the old Memorial Stadium, did yours?

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A man hears what he wants to hear, and disreguards the rest. Paul Simon

Thanks for posting your method. I haven't seen a description of deflection testing the braced top before.

Do you measure/care about the cross grain deflection of the unbraced top?

I have a couple questions about the part describing deflection testing of the braced top.

"This time readings are taken in both directions and I will gradually shave specific parts of my X bracing to obtain the desired movement in the desired direction. I work the upper section of the X toward the sound hole to adjust inward movement and the lower section of the X to adjust outward movement."

By 'both directions", do you mean with and across grain?
I'm not clear what you mean by inward and outward movement.

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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

I do not test the cross grain. I figure that having the plate cut to shape helps bring some of that into the measurement. Also if you were to test both ways you will likely find that you will need to choose one or the other to target closely for specified values and since the string tension is along the grain that is what I test and use.

On the braced top I am testing both directions meaning one with the braces down as in the photo and then flip so the braces are up and test. I didn't have a pic of testing the other way but will add one from my current build in a few weeks.

So with the braces down it is inward movement of the top and I shave the braces on the top of the X by the sound hole to adjust. When I flip it over I am measuring outward movement and am working the braces on the bottom. Hope that celars it up a bit.

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Brian

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

https://www.howardguitarsdelaware.com/

The brick was dropped off one day by a traveling businessman from another state who came to the area on business regularly and drove by my shop often. He had the brick for a long time and thought I should have it. Not sure where he got it but he was from Ohio.

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Brian

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

https://www.howardguitarsdelaware.com/

So what are you using for a baseline? What I mean to say is when one gets into deflection testing do you just pick an arbitrary weight, in your case a brick, and then use that to obtain data and consistent results from guitar to guitar? Or for some one who is just starting off doing this is there a sort of guide book that says if you use a 1kg weight and get X so and so deflection then so on and on?

What are you looking for? What are the numbers? The hard data?

OR do you just start doing this, take good notes, find what works and carry on?

I seem to get more consistent readings if I preweight the top a little, zero the dial and then add weight. Have you noticed anything like that?

How much does that brick weigh?

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It's not what you don't know that hurts you, it's what you do know that's wrong.

Here's a variation of the Roger Siminoff defection fixture -- best scenario is to use a sound board that produces the results that you admire to set readings you want to target. If can also be calibrated to simulate the effect of various string set tensions.

http://community.berea.edu/guitarresear ... Tests.html

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Ken Cierp

http://www.kennethmichaelguitars.com/

The problem with deflection testing is that there are no standards whatsoever. There are no guides that I am aware of and I am one of the few to actually share any specifics of the procedures I use. It took me several years to develop a data base and correlate it to my and others impressions of how the guitar sounded so that I could zero in on my sound.

I am sure if one wanted you could run modulus of elasticity calculations to determine weight vs. deflection but again you will not find much in the way a target numbers for guitars (as in L/240 like used for roof construction) published that I am aware of.

While I am happy to share my procedure and info about how I use it o tune the components I will keep my numbers to myself......Gotta keep a few secrets...

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Brian

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

https://www.howardguitarsdelaware.com/

Yes. I will put on my cork block and then zero before applying the test weight. I only need to do this on the bare plate.

My brick weighs in at a few grams over 2.5 Kilos.

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Brian

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

https://www.howardguitarsdelaware.com/

Ok so it really is all about establishing your own baseline. I get that. I actually like that too. That way we all won't be building the same guitars like they do in the factory and instead we can derive our own methods and procedures.

I've built 2 guitars out of the 60+ that I have built over the last 25 years that are, well to brag a bit, just astounding. Not that the rest suck but these two, one a classical the other a steel string, just sound perfect. So I guess I'll take the tops off those, strip the bracing, and do a deflection test

A number of people have talked about doing deflection testing ( I think Daniel Friederich does it) but there is no standard method so data sets can't readily be shared. It would be nice if a method could be agreed upon and a database be built up. A group effort could add a lot more data points than can be generated by individuals. Just a thought...

'Left Brain Lutherie' by David Hurd goes into deflection testing of tops in detail. He's mostly interested in Classical guitars and ukes, so there's no data on steel strings that I can recall. Still, he gives some useful info.