Thinning a top?

Working on a build right now using a donor neck from an old classical guitar that was busted up. Beautiful mahogany neck, and found a large cigar box that looks like it might either be mahogany or cedar. Proportionately, it's a great fit, and the color matches beautifully.

I've created the dovetail joint in the box to fit the neck, and am ready to start thinking about soundhole, bridge, etc. Before I do that, however, I've been thinking about the top. The box is about 3/8 inch thick on all sides, so I'm thinking it's not going to vibrate terribly well. I was wondering if I took a Dremel and thinned out the top, if that would create a better sound, assuming I sort of "built-in" some bracing by only thinning certain parts and leaving the wood thicker where traditional bracing would be.

What do you think? Is this a crazy idea? Worth the work involved? The neck is from a classical guitar, so I'm not thinking I'm going to be able to do steel strings, which I would think would help with the thickness of the top.

Replies

Michael Fred Johnson August 2, 2014 at 11:33am

The top on this was about 3/8" thick.I routed it down to about half that thickness leaving two 1/2" wide strips the original thickness running across the box to act as braces
Ron "Oily" Sprague August 2, 2014 at 9:33am

Not a crazy idea. Easy to do with a plunge router with the appropriate depth set. You can also leave "braces" in unrouted areas if you want (several people on CBN have done this; use the Search for "routed tops" to find example pics). Rout it down to 3/16" thickness. But do it only after you test it unrouted, per Wayfinder's suggestion; you may find it doesn't need it. You can always go back and thin the top if you want.
RTZGUITARS July 28, 2014 at 6:05pm

I sand the top of some boxes down to 3/16 as long as you don't put to many sound holes you should be fine. The area of a normal cigar box top you probably don't need bracing. You want the top to move so less is more.
John Sawyer July 28, 2014 at 4:09pm

Probably a good plan. Like others have mentioned, it might require bracing to keep it intact.. If you take Wayfinder's advice, and screw it closed, you could alter it later, if desired...

I've built about 20 CBG's and 1 Uke to date. Of all the boxes I've used, most are some sort of plywood. The Perdomo box I have isn't ply, but the wood is really soft...
Paul Marchese July 28, 2014 at 12:36pm

Definitely not plywood, John. Not sure exactly what it is, but I've cut into it to create the dovetail fit, and it's definitely sold all the way through. I think I'm probably going to just leave it as is, make sure to put a piezo under the top or under the bridge, and cut F-Holes into it...
Muddy Creek Guitars July 28, 2014 at 12:05am

I occasionally have thinned a thick lid. I use a palm router with the depth set VERY carefully. It will remove a fairly uniform amount from wherever you want. This also helps with "stick through" construction as I don't have to notch so much off the stick, making it too weak. BE CAREFUL! making the lid too thin makes it VERY FRAGILE!!

Good Luck!
John Sawyer July 27, 2014 at 10:01pm

Don't forget Scale length! That will have to be a good sized box for the bridge to be in the right position...
- John Sawyer > John Sawyer July 27, 2014 at 10:56pm
  
  Damn smartphone. Plywood.
- John Sawyer > John Sawyer July 27, 2014 at 10:55pm
  
  They are mostly lkywood. I would bet planing it would result in disintegration. Just put a new lid on it... Luan ply would work if braced, IMHO.
- Paul Marchese > John Sawyer July 27, 2014 at 10:11pm
  
  Scale length will be no problem!
  
  Can't plane it without taking off the top entirely and changing the entire thickness of the top, to my knowledge.
  image.jpg

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