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How thin is too thin for Lutz spruce?
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Author:  John Elshaw [ Sat Jan 06, 2007 6:06 am ]
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Well, after four years of building classicals I'm finally giving it my first shot at a steel string. I'm using the OLF SJ plan. I made the top months ago when I was building 3 classicals, and I thinned the top to 2mm, the same as my classicals. After watching the Ervin Somogyi videos on this site, I'm thinking I may have taken the top too thin. Is 2mm too thin for Lutz Spruce, or is it possible to keep the top and just brace it a little more? I haven't used Lutz spruce before so am unsure what to expect, especially with a steel string.

Thanks!

John     
Author:  dgalas [ Sat Jan 06, 2007 6:55 am ]
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The question should be how loose is too loose. With braces and doming
you will be adding great amounts of stiffness, which then in turn gets
loosened back up through carving of the braces. The strings have no clue
how thick a top is, but they have an intimate relationship with how stiff it
is.

It sounds simple, but I hadn't really thought about it that way until I took
Ervin's class. Now my tops are thinned to a certain stiffness. The problem
is there is no easy way to pass that 'stiffness' number along like one can a
thickness number.

The other thing I learned in Ervin's class is that everyone overbuilds tops
at first. With consideration to how stiff the Lutz I have is, and how thick
my tops ended up after sanding to a certain stiffness (this is the "all
things being equal" part of the answer ), I would say definitely use it.
Use it, take notes, see how it comes out. Good Luck!

Cheers,
-Dave
Author:  peterm [ Sat Jan 06, 2007 6:56 am ]
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I'm sorry but I have to say the same as Hesh... way too thin. Besides after final sanding it will even be thinner. I guess you'll have to make another classical with that one!
Author:  dgalas [ Sat Jan 06, 2007 7:35 am ]
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Hesh, how dare you!?!?!

Actually, giving it further thought, and considering it is a first steel string,
I would recommend building two. I now build two at a time side by side
so I can compare them as I go. I see this as a perfect opportunity. It
reminds me of an article a couple years ago in AL where the author built
two identical kits but made the top on one of them extra light. I think he
referred to it as his Ferrari version.

The biggest thing I learned in Ervin's class is that this is a complex beast
and I now look at each guitar I build as an opportunity to learn more
about it. I'm always reminding myself to pay attention to how any change
no matter how subtle changes other things, take notes, and seek
opportunities to learn more. I see this as an opportunity, and I think the
quality of the final instrument might be surprising.

So there!
Author:  Serge Poirier [ Sat Jan 06, 2007 8:12 am ]
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Hesh and Dave, will you guys quit bashing each other with so much kindness pleeaase?

I gotta say that i'm with Dave on this, i for one always feared making mistakes on all my builds so far but never forgot to embrace them for everything they can teach me and i'd encourage John to use this very thin top having fresh in mind what Ervin Somogyi said about featherweight monocoques building and there is just one way to verify that, build it and see!
Author:  John Elshaw [ Sat Jan 06, 2007 8:20 am ]
Post subject: 
Thanks for the input fellas! The stiffness arguement is valid and made me think of another question. Have any of you who built an SJ size guitar done any deflection testing with Lutz spruce? A deflection test in several directions might be a better way to judge stiffness. After all, I have built a bunch of classicals so judging stiffness isn't completely foreign to me. Also, after remeasuring the top, it is closer to 2.2mm in most spots so final sanding etc. should still leave it around 2mm+. I know you guys said don't use it, but you're right about using it as a learning opportunity. Since this is my first SS, I know I won't be selling it, so this might be a good chance to push the envelope (inadvertantly) to see how thin I can go on top. After all, it's unlikely I'd go this thin again on purpose in the future, so this might be the only chance to really learn from a top so thin. I like the idea of building two side by side--I think I might have to try that.

Cheers!

John
Author:  Serge Poirier [ Sat Jan 06, 2007 8:39 am ]
Post subject: 
John, i am building an SJ right now with a red cedar top that was very stiff along the grain and really floppy across but the parabolic bracing that Colin taught me helped make that top tap really nice now that my box is closed.

I'd say that as long as your top is thicker in the center where the bridge will go and your bracing very stiff that it would make a very responsive top IMHO, i would certainly use it with high hopes!
Author:  dgalas [ Sat Jan 06, 2007 9:24 am ]
Post subject: 
John,

Like most wood, I have found Lutz to vary quite a bit even in the same
billet. I have some tops that are really stiff and others from just 3/4" away
in the same billet that are pretty floppy.

My senses aren't nearly as refined as Ervin's so I still take deflection
readings as I sand them down to my final thickness. Two Lutz tops I
recently sanded to the same stiffness varied in thickness by 15% or so. By
the cube rule, we know that if the wood had been identical, the thicker
top would be 50% stiffer. What I'm getting at is each slice of wood has to
be evaluated individually.

Hesh,

You're a big jerk. (I'm working on tempering my likableness )
Author:  JohnAbercrombie [ Sat Jan 06, 2007 9:27 am ]
Post subject: 
[QUOTE=dgalas]
The problem
is there is no easy way to pass that 'stiffness' number along like one can a
thickness number.

[/QUOTE]
Dave-
You're right in that it is certainly more difficult to gather stiffness info in a standardized way.
However, I think it would be great if we could agree on some simple deflection test so that we could get some numbers and start being more systematic.
There was an article in the GAL about a mandolin class where the tops/backs were carved to a stiffness/deflection standard- I thought it was interesting.
Basically we'd have to decide on how the plate is to be supported, the amount of weight to be applied and then measure the deflection using a dial indicator.
If y'all would just send me your old Martins and handmade guitars, I'd be happy to do the measurements!
Cheers
John
Author:  TonyKarol [ Sat Jan 06, 2007 9:42 am ]
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send me your old Martins ... well at least the good sounding ones .. there was one at a store here, a 56 D18, and the best thing you could do is look inside, measure everything, and then stay the heck away from those measurements and brace pattern/sizings !!! It was one of the worst sounding martins (or any guitar make for that matter) I have ever heard -and they wanted almost 6K for it, because it was old - big deal. Pretty much every Garrison on the wall sounded better.
Author:  James Orr [ Sat Jan 06, 2007 9:44 am ]
Post subject: 
Here's a question about measuring stiffness.

I have a little device I made for tuning drums. For those that don't
know, I built drums before coming here: http://www.languagepool.net/
images/setSilhoetteClosest.jpg It's just a dial-indicator shoved
through a hole in the middle of a hockey puck. You put it next to each
lug, and tighten or loosen until the dial indicates the same number on the
indicator, measured in thousandths of an inch just like our calipers.

Couldn't something similar in concept be put together to measure
stiffness as long as the tops were of the same width and length?   
Calibrate zero on the indicator and it should be a reliable way to
communicate stiffness.

My little dial works because the puck is somewhat heavy and wide. The
needle in the indicator pushes the drum head down and as you tighten or
loosen the head, the needle moves up and down in a work space of
around 30 thousandths. When it's within two thousandths at each lug,
the drum is in tune. It's fast, and all I need to do is remember which
number produces the sound I'm after because the results are controlled
and not relative to what I think it feels like--because my senses can
change daily.      
Author:  dgalas [ Sat Jan 06, 2007 10:23 am ]
Post subject: 
[/QUOTE]

Thanks Dave - but at least I look good in a bikini....... [/QUOTE]

How thin is too thin?
Author:  John Elshaw [ Sat Jan 06, 2007 10:46 am ]
Post subject: 
[QUOTE=James Orr] Couldn't something similar in concept be put together to measure stiffness as long as the tops were of the same width and length? [/QUOTE]

I don't think you even need to have the tops be the same length. As long as the supports on both ends are consistently spaced, say 18 inches, it wouldn't matter how long the top was. Here's a pic with a 1kg weight testing deflection. We could really get a lot of good data if everybody would do this. If the OLF created a database of deflection testing to some standardized specs, it would be invaluable. It only takes about 15 minutes to build a rig like this, and about 10 seconds to measure a top.



Author:  Brock Poling [ Sat Jan 06, 2007 11:25 am ]
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[QUOTE=peterm] I'm sorry but I have to say the same as Hesh... way too thin. Besides after final sanding it will even be thinner. I guess you'll have to make another classical with that one! [/QUOTE]

I can't answer the question about that specific piece of wood, but I can tell you that I have seen tops that thin.

Author:  j.Brown [ Sat Jan 06, 2007 11:43 am ]
Post subject: 
My last guitar was 1.9-2.0mm on the top. Its been through a lot since I finished it in may. Played LOTS of gigs, lots of travel...hot, cold, dry, humid, etc. and it hasn't shown signs yet of having any trouble.
The X braces were laminated with Graphite, but not overbraced....
I think it was probably at the brink of being too thin, but not quite. It sure is loud, though.
-j.
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