Official Luthiers Forum!

hi all
has anyone done any deflection testing on a completed guitar soundboard as it moves whilst tensioning the string up to pitch? I think this information could be useful, it’s just completing the circle of individually testing the braces and soundboard plate components, with bridge / bridge plate as a complete unit.
If you think this is taking things to far please put me right!.
yours Geordie

_________________
some tunes on acoustic and guitar synth.
http://www.youtube.com/user/TheGeordieAdams
http://www.myspace.com/geordieadams

Geordie,

I think if you get it so that the top will successfully deflect a thrown pint of Guiness in a crowded bar when the act isn't going too well, and you can seamlessly go into the next tune then you've probably got it about right.

_________________
Dave White
De Faoite Stringed Instruments
". . . the one thing a machine just can't do is give you character and personalities and sometimes that comes with flaws, but it always comes with humanity" Monty Don talking about hand weaving, "Mastercrafts", Weaving, BBC March 2010

Dave
we must enjoy the same kinda “watering hole” - "a thrown pint of Guiness in a crowded bar" - only when Scotland (soccer) is snatching defat form the jaws o’ victory
Geordie

_________________
some tunes on acoustic and guitar synth.
http://www.youtube.com/user/TheGeordieAdams
http://www.myspace.com/geordieadams

OK Dave...I just have to say that I chuckle at your responses, I really appreciate your light-hearted approach to all of this, you would be a fun chap to hang out with.

Cheers,

_________________
Gwaltney Guitars

Oh my!!! I do need to make a UK visit one of these days. You blokes are too funny!

_________________
JJ
Napa, CA
http://www.DonohueGuitars.com

No, no, no Dave mon....... don't you want the top to "catch" the pint of Guiness and even keep it upright so that the player can retrieve it and subsequently drink it? This may in fact be why Ovat*ons were bowl shaped........

Reminds me of the scene in the Blues Brothers where they are playing on a stage behind chicken wire........

That's what a soundport is for but you have to be really skilled and confident to carry that one off. Deflection to another waiting band member is probably a better option.

Geordie - sorry for the hijack, I'm sure the deflection gurus will be along presently to give you sage advice.

_________________
Dave White
De Faoite Stringed Instruments
". . . the one thing a machine just can't do is give you character and personalities and sometimes that comes with flaws, but it always comes with humanity" Monty Don talking about hand weaving, "Mastercrafts", Weaving, BBC March 2010

Would you guys please keep the political discussions to a minimum. We may have to block this thread.

_________________
Waddy

Photobucket Build Album Library

Sound Clips of most of my guitars

David Hurd, AKA 'Kawika', published a book a few years ago, 'Left Brain Lutherie', that had a lot about the deflection testing he does. It's pretty technical; he leads off with a couple of pages of variable names that he's going to use in the equations, but that's all sort of the orchestratinoin the bass. The melody was about using deflection data to help you get consistent sound. I think he was doing with deflections what I do with 'plate tuning': getting the right balance of stiffness, and degree of stiffness, with his braces and top wood. You could try getting in touch with him: iirc his web site is ukuleles.com, although I have not looked in on it in some time.

Bwahahahahaha!

_________________
Howard Klepper
http://www.klepperguitars.com

When all else fails, clean the shop.

Geordie,
I've done some this to verify some structural computer models I've made. I remove the tension from the strings and span a dial indicator across the lower bout , zero out the indicator, mark the spot on the top and fixture locations , re-tension the strings and place the indicator back on the exact same spot and fixture locations, then read the deflection. I'll try to get a picture for you of my set if you'd like. It's quite simple.

_________________
Jim Watts
http://jameswattsguitars.com

hi all
Many thanks for your constructive contribution.
Alan C. & Jim W. The Quality Control hat was on for me to have asked the question initially I wondered, why test before and not after, that's all.
With the variability of materials and structural design it seemed necessary to acquire this information to optimise the components in our model.
It’s not a difficult test to set up as you suggest Jim and yes pictures of your method please.
Observing differences in the string plane is something we do instinctively when fitting different string gauges or stringing up a new instrument I just think it might be beneficial to take some data.
yours Geordie

_________________
some tunes on acoustic and guitar synth.
http://www.youtube.com/user/TheGeordieAdams
http://www.myspace.com/geordieadams

Yes, David Hurd’s does have photos and instructions for measuring top compliance. He appears to have done this testing on a closed body but before the neck, strings, and bridge. David’s site has a good deal of information if you look around. It does have a site map and a search engine to help you find what you want. I really like his jig for measuring string properties. You can measure for any size ukulele and use the measurements for compensation.

http://www.ukuleles.com/Technology/compliance.html
http://www.ukuleles.com/Technology/compensate.html

Philip

_________________
aka konacat

If you think my playing is bad you should hear me sing!
Practice breeds confidence and confidence breeds competence. Unfortunately, I'm stuck in practice.