Official Luthiers Forum!

In watching Johns DVD's I noticed he thicknesses his tops around 0.125 or
so.   Is that what most of you do? I was thicknessing around 0.11 to 0.115.
I am curious what all of you do. I know it depends on the wood, stiffness
etc. But what is your typical spruce and cedar top thickness. (Prior to final
sanding etc.)
Thanks
Andy

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

0.113 is what i obtained on my first but i could have easily stopped at 0.125, bringing it down to 0.113 made me quite nervous!

I've built only one steel string acoustic so far. The top was an exceptionally stiff set of bearclaw sitka so I thinknessed it to 0.110". It was still plenty stiff, even at that relatively thin thickness.

Best,

Michael

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Live to Play, Play to Live

based on stiffness. I start at .125 prety typical but may go down as low as .108 in some cases

For spruce I start at around 3.2mm (0.125") in the centre and then thin out around the edges and behind the bridge. It depends on the piece of wood where it goes from there, but thicker in the centre is good for trebles I find. On the one WRC top that I have made I treated it the same as spruce.

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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

How should I be testing stiffness? And how do I relate stiffness to thickness?

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53% of all statistics are made up on the spot
http://driftwoodguitars.blogspot.com/

One way to test for stiffness is a deflection test. Set your soundboard on top of two pieces of straight aluminum or steel which are 18" apart. Put a 1-kg weight (or some other constant weight) on top of the soundboard and measure the amount of deflection in the wood. Take note of the thickness of the material as well as the deflection. If you do this every time, you may start to see a pattern in some of your guitars which turn out really well as far as stiffness and top thickness.

Good luck!

John   

Yep deflection test but you need a comparitive. This one of the things that goes into a build journal so you can look back and compare.

The build journal is a good idea. I didn't even take pics of the first one. The second one already has the braces glued on. Guess I'll start with #3.

_________________
53% of all statistics are made up on the spot
http://driftwoodguitars.blogspot.com/

I generally work around 0.085" on my classical tops but exact thickness
depends on characteristics of each piece of wood and also on other
things like bracing design etc.

My spruce tops normally range in thr .125-.100 range. the latter for very
stiff pieces. If you go too thin your risking lots of bellying, and/or a dark
tone (breedlove-esque) which I don't like. It all depends on stiffness and
weight.


And for the rap song... ok here is a clue.... check the quiz.... that's all I'll
say. I know two people have found it....

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John Mayes
http://www.mayesluthier.com

I'm an oddball, I guess: I start with most steel string tops around .140 (3.5mm). However, I taper them out behind the bridge, sometimes to as thin as .095 or less at the tailblock. Cedar is about 10% thicker.

I believe Dave Hurd gave at least two ways to measure the Young's modulus of your wood: by deflection testing and by resonance. Both can be pretty easy to do these days, and give results accurate enough for our nefarious purposes.

Write stuff down! Some folks seem to be able to remember what they did on every instrument for the past ten years. I'm lucky if I can call to mind what I had for breakfast: and it's usually the same thing! The only problem with keeping records is that the more you do the more things you'll think of that you need to write down. I have a file folder on each instrument, with a half dozen pages of daigrams and such, and I transfer some of the most important info to a single page that I can keep in a notebook for easy cross-reference. It's great, when you build a particularly nice one, to be able to go back and copy it more or less closely.   

Alan,

I remembered you mentioning the file folder when you were speaking at the ASIA 2003 symposium and it was for me one of those "aha" mements.

After you mentioned the file folder that you keep to document all details of a particular instrument, I have started doing it for each instruments and it really helps. I had always kept notes but now even make a point of telling customers of the file folder I keep for each instrument so at any point in the future I can refer to it as needed.

I believe that you also said that you make notes as to the "glitter pattern" voicing (frequencies, modes, etc) which was the other thing that I picked up in that workshop. I keep that in the file folder as well.

That workshop has continued to help me to get more consistent results by being able to hear (by Chaldni tuning) and recall (via a file folder) the small details that make a difference. Thank you.

I build classicals and also make tops generally thinner behind the bridge area.

Shawn:
Glad that's working for you.

I got the idea originally from George Bowden in Majorca, before I ever made any guitars. He sold one to a fellow who was on vacation, and took it home with him to New Zealand. About a year later George started to get letters from folks asking for one just like it, and he couldn't remember what he'd done! We all tend to experiment from time to time, and even the normal variations in woods amount to a certain kind of experiment, whether we mean it that way or not. It almost doesn't matter what you keep track of, just so long as you have some notion of why it might effect the tone. After a while, you'll see in your records what works and what doesn't.

In addition to important information of each instrument I've found it invaluable to journal about things that work and don't work. Mine started with the realization that the sides should be supported when gluing to the top or else they won't keep their shape. Now about 20 single-spaced pages later I've found that by going over what works and what doesn't, I can think more clearly when I'm actually doing things. So in addition to having important deflection/resonance/thickness measurements you also have records of how you most efficiently got there. This forum, i suppose, works in that sort of way too.