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Thickness of top
http://mowrystrings.luthiersforum.com/forum/viewtopic.php?f=10102&t=15283		 Page 1 of 1
Author:  MichaelV [ Mon Jan 07, 2008 8:39 am ]
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Hy everyone,

I'm new in this forum and I'm building my first guitar. It's a classical with cut away made with Western R cedar and Indian Rosewood.

I will use a 5 struts fan bracing.

I supposed that the cut away will have an impact on the sound, probably on the treble. I'm planning to have a 2.5mm thick in the lower bout and 2.2 mm thick around the sound hole.

To correct the sound I'm planning to put the top at 2mm in the cut away area. Someone know if ti's a good idea ? Other suggestions ?

Thanks
Author:  Michael Dale Payne [ Mon Jan 07, 2008 9:44 am ]
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My Hauser Sr. Palns call for 2.3-2.4mm at the bridge and sound hole and reducing to 1.8-2mm at the edges For Cedar.
Author:  JohnAbercrombie [ Mon Jan 07, 2008 10:41 am ]
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Michael-
With a traditional bracing plan, I don't think you will find that the upper bout is very 'alive' anyway, especially in the cutaway area, so I doubt that making the top thinner in the cutaway will pay back very great rewards in terms of the sound you get.
You do want to keep in mind the structural functions of the upper bout (supporting the fingerboard, etc).

Cheers
John
Author:  WaddyThomson [ Mon Jan 07, 2008 1:57 pm ]
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[QUOTE=MichaelP]My Hauser Sr. Palns call for 2.3-2.4mm at the bridge and sound hole and reducing to 1.8-2mm at the edges For Cedar.[/QUOTE]

Those sound like Spruce numbers, Michael. 
Author:  Alan Carruth [ Tue Jan 08, 2008 6:46 am ]
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See the thread on 'Deflection Testing' for a post on how I determine the 'proper' thickness for a top. You can't just assume that any WRC top will act like any other, or need the same thickness. The only way to know for sure what will work is with some sort of measurement. The 'old boys' did it by feel and by eye, and that's great once you have some practice. Until you get that, numbers can be a real help.   
Author:  Michael Dale Payne [ Tue Jan 08, 2008 7:00 am ]
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Umm Mabe you are right I will check tonight
Author:  MichaelV [ Tue Jan 08, 2008 7:03 am ]
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Thanks,

I agree that the upper bout is not the most important part for sound generation. My front is flexible and I will go with a thickness of 2 in the lower bout and 2.5mm in the rest of the top.

Regards
Author:  Alexandru Marian [ Tue Jan 08, 2008 7:21 am ]
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Also Hauser did not build in cedar!

I think the best way to go is to overbuild it a little.   Try to taper the thickness the top like in the image on the right:



My advice is to add 0.1 or even 0.2mm to the center.  You have no ideea what a stiff or floppy top is. You might know after handling and building with a heap of them .

Make the strutting as you picture it should be. Copy your plans or the internet pics you use as inspiration.  

I am saying try not to overbrace, it is hard to fix through the soundhole.

A thicker top can be easily sanded from the exterior if it ended up too stiff.

A cutaway takes some of the box volume, but it should not influence your take on the lower bout.  If you build a modern sized large guitar it will still be larger than a tiny Torres or Hauser. It will have good bass if you get the top right.

Author:  WaddyThomson [ Tue Jan 08, 2008 8:07 am ]
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 The 1937 Hauser (Segovia Model) top measurements varied from 2.21mm to 2.69mm at the edge on the bass side and 2.39 to 3.08 mm at the edge on the treble side, and, with lots of variations in measurement tapered to 2.79mm on the sound hole side of the bridge. Fairly thick for a Spanish Style build of the time, per Brune, and was most certainly spruce, as I think Alex is right.  He didn't build with Cedar.  I just happened to have a copy of the plan here in my office.
Author:  Alexandru Marian [ Tue Jan 08, 2008 8:30 am ]
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Yes that is quite very thick, BUT, if his famous spruce stash was from a lower than average density tree, we already have more thickness than normal. 
Does the plan tell what is the bridge weight?  When making a copy its equally important to match the bridge density too, not just the top material.

And so on...
Author:  Alexandru Marian [ Tue Jan 08, 2008 8:34 am ]
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Waddy, I am curious, does it say/do you remember, where was the edge thicker?
Author:  WaddyThomson [ Tue Jan 08, 2008 8:38 am ]
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The bridge was quartered Indian Rosewood 27x187x8.5-8mm.  Wings were 4.5mm rounded.  Don't know about density, but Brune commented on it being a stiff bridge.
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