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[QUOTE=Rick Turner] Anyone like to comment on this dismissal of Young's Modulus?

http://www.lucchicremona.com/EN/tester_tester2.htm[/QUOTE]

Hey Shane,

As well as those essential "lumberjack items" you already have - high-heels, suspenders and a bra - it looks like you are going to need a Lucchi Minipalm Meter to take into the woods with you from now on

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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

[QUOTE=Rick Turner]Anyone like to comment on this dismissal of Young's Modulus?

http://www.lucchicremona.com/EN/tester_tester2.htm[/QUOTE] 

 

 WOW Rick !  nice find .. this brings about some interesting basic knowledge .. and of course more questions !  LOL

 

 

I met and spoke with Giovanni Lucchi at the Frankfurt Musik Messe in 1989 and purchased an early version of the Lucchi "meter" for Gibson at that time.   I have no idea if they have ever really used it for grading wood in production, but they've had one for nearly 19 years.   It's very interesting, to say the least.

Jody I repaired the link here:

http://www.lucchicremona.com/EN/tester_tester2.htm

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Ann Arbor Guitars

[QUOTE=Alan Carruth] I have not published that myself. I learned the method from Mort Hutchins, who got it from Dan Haines. Both of them published articles in the Catgut 'Journal' about it, but that was a while ago ('81), and some of you may not have copies.[/QUOTE]

If only Mom and Dad had known I'd eventually want to build guitars a year before I was born and gotten a subscription, we would have avoided all this trouble!

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Bob Garrish
Former Canonized Purveyor of Fine CNC Luthier Services

[QUOTE=Hesh]Jody I repaired the link here:

http://www.lucchicremona.com/EN/tester_tester2.htm
[/QUOTE]

 

 thanks Hesh, I changed the link unknowingly....Jody

[QUOTE=Dave White] [QUOTE=Rick Turner] Anyone like to comment on this dismissal of Young's Modulus?



http://www.lucchicremona.com/EN/tester_tester2.htm[/QUOTE]



Hey Shane,



As well as those essential "lumberjack items" you already have - high-heels, suspenders and a bra - it looks like you are going to need a Lucchi Minipalm Meter to take into the woods with you from now on [/QUOTE]

I wonder how well that little puppy works when you up to your arse in snow looking at logs like I was today!!



So many methods, so little time!!

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Canada

[QUOTE=Jody]

[QUOTE=Rick Turner]Anyone like to comment on this dismissal of Young's Modulus? http://www.lucchicremona.com/EN/tester_tester2.htm[/QUOTE]

WOW Rick ! nice find .. this brings about some interesting basic knowledge .. and of course more questions ! LOL

[/QUOTE]

I don't believe this is a dismissal of Young's Modulus at all. I believe it is simply pointing out that it is the ratio of Young's Modulus to the density that is critical. They are highlighting the fact that wood with high stiffness and low weight is generally the most desirable.

Also, you really don't need to do any sort of vibration test to get a value for Young's modulus (see my previous post). I think that you'll get a much more accurate value for Young's Modulus if you determine it thru a deflection test...the deflection test directly measures stiffness whereas a vibration test indirectly measures it. It would be easiest to test for this value using a smaller piece of material than half a top.

Also, there is an inherent problem with analyzing vibration: as soon as you a)fixture the part and b) attach anything to it you have altered your results. The boundary conditions (i.e. what the part is resting on) can also have a large effect on the values that you will obtain. You can imagine how differently a part will vibrate if you have both ends firmly clamped versus each end resting on a piece of foam.

Long story short...if you use wood that is really stiff and really light, then you don't need much of it in order to build a structurally sound top. Since it is lighter, it also moves more than a heavier top would...this results in more volume. That's why you use spruce instead of ebony for guitar tops.

This is pretty much what my training and work as an engineer has led me to believe. I'll look forward to either proving them wrong or confirming them; in either case I'll gain a little more understanding.

The real trick will be when we convince someone with Finite Element Software to run some good analysis for us. ....I used to have access to the good stuff but I have since switched jobs.

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http://www.PeakeGuitars.com

Now we're getting somewhere.   

Parser, I understand and totally agree. What I was trying to point out is that if you can't see the forest for the trees and are solely looking at one number...Young's modulus, for instance, you'll be on the wrong track, even though what you are looking for...specific stiffness...is valid.   

I've been following Lucchi's work for close to 20 years, and I've watched the violin world bit by bit adopt Lucchi numbers as being very accurate in predicting response, particularly of violin bow woods.   Now the odd thing is, for us guitar maker-types, that great violinists attribute a huge proportion of their tone to the bow itself. This is why really good modern violin bows cost in the region of what we consider high end guitars...$5,000.00 and up. Great vintage bows rival great vintage guitars in cost these days; they're in the tens of thousands of dollars.

Lucchi, a past president of the Cremona Violin and Bow Makers Association (or Guild or whatever), told me that before he started using the meter...which really just measures the speed of sound through the wood and the Q...he really didn't know whether a particular well chosen stick would yield a decent bow or a great one...given that his craftsmanship was right on up there no matter what.   But when he started to literally see this relationship between speed of sound and specific stiffness then coupled with density, he could simply eliminate all the lesser Pernambuco and only build with the best wood.   Twenty years ago his work was very controversial...too much science, not enough smoke and mirrors.   Today Lucchi numbers are well accepted in the violin world as an indicator of how good the wood is.   Of course, then you have to know what to do with it.   

There's always a catch!

I agree with parser on this, but the bottom line is either method gives you the same number.

I didn't check out the link yet, but i believe the Lucci meter is measuring the speed of sound? If thats true, then the density and modulus determine that.

On the FEA stuff I've been doing the frequency analysis on a variety of tops using the orthotropic properties that I've measured from my stash (deflection testing and a triple beam balance) and am close to putting some test tops together. Soon I hope.

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Jim Watts
http://jameswattsguitars.com

Yes, the Lucchi meter measures the speed of sound and derives the Q. Modulus AND density count. Not just one, not just the other.   Both is where it's at.   Stiff and heavy doesn't cut it!

  in basic lay-mens terms , I think the lucci method is measuring the damping , or lack of damping  of each particular cut of wood.. Jody

It looks like someone is selling those meters, but I can't find an obvious link where they are doing that.

Any idea what these cost or where to get them.

This is a great thread.

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Brock Poling
Columbus, Ohio
http://www.polingguitars.com

I believe the meters are available here:

http://www.bowworks.com/pages/catalog/miscprod.php#Anchor-LU CCI-22647

About 2,000 Euro.

 

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Jim Howell
Charlotte, NC

2,000 Euro!!!

Now one of these meters would be a cool thing to include in the 2008 OLF subscriber package - who needs a stinkin cup anyway......

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Ann Arbor Guitars

Yeah, about $87,000 American at current exchange rates or a paltry two gold crowns (molar, not incisor)! 

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Jim Howell
Charlotte, NC

Here's something else I have run across:



here's the source article: Wood for Sound
http://www.amjbot.org/cgi/content/full/93/10/1439

Referring to the chart above, if you draw a line from the origin of the chart to any one location the slope of that line indicates the relative "tone" of one wood to another. The steeper the slope, the more higher pitched the wood and vice versa.

Another observation I think we can make is that most of the woods charted out have a similar slope...but some are further along that slope than others. You basically have soundboard woods halfway up the slope and violin bow woods at the top. What would be really cool would be to plot out these values along with cost per board foot. I'm willing to bet that would explain why we use spruce for tops and reserve woods like pernambuco for violin bows.

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http://www.PeakeGuitars.com

also - CFRP at the top stands for Carbon Fiber Reinforced Polymer. I guess they threw it in there just for the heck of it..!

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http://www.PeakeGuitars.com

Now if we could just see the Q or damping factors...

Parser:
Haines had some discussion in his articles on the determination of wood properties about the various methods that could be used. None of them is perfect, and it helps to understand the limitations of each.

One issue with deflection testing is the cold creep of wood. If you load a piece with enough weight to deflect it by a measureable amount, you will find that the deflection changes over time. If the load is retained for some length of time the wood does not spring back completely. Vibration testing gets around this by alternating the load.

Vibtration testing yeilds not only the two E values but also the associated damping factors, which I consider important. With deflection testing you have to do a seperate test to find the damping, and it will involve vibration. Why not get both sets of numbers from the same test?

If vibration tests are carefully done the E values are quite as accurate as those gotten from carefully done deflection tests.

I'm not saying my method is 'perfect', but it gives me information I can use, and I posted it in the belief that other folks might also find it useful. Do what works for you.   

The interesting thing about the Lucchi testing setup is that you can run as many tests as you like along a particular path through the wood.   As I understand it, his methodology is derived from ultrasonic non-destructive testing methods that can find hidden flaws in materials.   It's kind of like sonar in that sense.   His "meter" was originally designed by a guy in the Italian nuclear research biz and came out of ways used to test containment vessels.   

Al, have you tried one of the Lucchi meters?   I know it's not cheap, but it sure is convenient and portable.   

Al, that's excellent that you have figured out a good method for testing for these values. I have done very little wood testing myself, and my comments were meant as general advice (I do have a good bit of experience with vibrations analysis). Specific experience and advice like yours is worth it's weight in gold - thanks for sharing!

I would bet that damping changes with moisture content...?    That's my guess..I'm thinking that's why some people bake their tops.

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http://www.PeakeGuitars.com

I haven't tried a Lucci. I've talked with people who use them a lot, though, and, as usual, there are plusses and minuses. One issue is runnout: a bow blank that runs out a bit sometimes won't return a good signal, or so I'm told. That's a reason not to buy it, of course. I have to wonder what the results would be on a somewhat curly back, like some of the myrtle/bay that I've got. I suppose I'll have to get one a try it.

I'm not sure if the method I use is all that wonderful: it seems to work, but it's far from perfect. In the end there is no simple way to make really high quality measurements, so the question becomes; what's the simplest way to make adequate ones? It could be that, in some cases at least, my measurements are less than adequate. I'll find out at some point; I hope it's not the hard way! Usually is....

"I would bet that damping changes with moisture content...?    That's my guess..I'm thinking that's why some people bake their tops. "

I'm told it does, but I've never done the experiments myself. Mass goes up and stiffness down as the R.H. rises, of course, and that alters the pitches of modes.

Baking is supposed to drive out all, or most, of the bound water. I've read that it's the hemicellulose that absorbs most of the moisture, and that branched chain polysaccaride is always breaking down slowly. Driving off the water is said to stabilize the wood, perhaps eliminating the binding sites for water molecules. This could, of course, stop or slow the degradation of the HC, and that might be a bad thing. As the HC degrades the wood becomes less dense and stiff, but the density falls off faster, so the stiffness to weight ratio rises.

I would think that a bow that has runout not returning a good signal would be a good thing! Runout is not a good thing... I've watched as the Lucchi meter has been slowly accepted in that very closed violin world.   Might just have to get one someday.   Hmmm, sell a guitar, get a Lucchi meter...

I see there has been a misunderstanding. I said that getting a poor signal back from a bow blank with runnout was 'a reason not to buy it'. I meant buying the bow blank, not the Lucci meter. In that case, the meter has indeed worked well. The point was that we sometimes like to use wood, such as the curly laurel/bay that I have, on guitars, and I wondered if the meter would return a proper signal from such a piece.

My bad.