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Thinning already glued guitar top?
http://www.luthiersforum.com/forum/viewtopic.php?f=10101&t=36047		 Page 1 of 1
Author:  SixStringer [ Sat Apr 07, 2012 3:15 pm ]
Post subject:  Thinning already glued guitar top?
I am finishing up an old guitar build I started a while ago. From what I 'know' now, the top probably needs to be a bit thinner, a good bit. I am just plowing ahead with this, can't really take it off because some of the binding channel is cut, etc. (not a really good build, but its almost done: Bridge,Back, binding, string it up.)
What is the best way to thin this top out?
Author:  Jim Kirby [ Sat Apr 07, 2012 3:25 pm ]
Post subject:  Re: Thinning already glued guitar top?
It's not uncommon for people to get to the final thickness (particularly in the classical guitar world) simply by sanding the top after all the assembly and binding is done. Even if the main part of your top is too thick, you may gain a lot simply by sanding around the lower bout perimeter, provided your bracing isn't too heavy near the edges of the soundboard. How much do you think you have to work with?
Author:  Colin North [ Sat Apr 07, 2012 3:32 pm ]
Post subject:  Re: Thinning already glued guitar top?
For me, I would bind first if you have plenty depth then use a block plane then scraper to smooth things off. Watch the direction of planing and scraping for any runout.
Make a scratch block (piece of MDF with edges relived and a nail sharp end sticking out a known distance)
You can scratch the top to a known depth and go to it with the plane and scraper.
I've used this technique to taper the edges of a top so I have an good idea what's left.
Author:  David Newton [ Sat Apr 07, 2012 4:02 pm ]
Post subject:  Re: Thinning already glued guitar top?
I wouldn't bind it yet.
Block sand it with 150 till it is pretty close to where you want it. Seal the edges with shellac, finish cutting the binding channels, and bind it.
Level the binding.
Then take the sanding to 220 & 320 & finish.
Author:  SixStringer [ Sat Apr 07, 2012 5:45 pm ]
Post subject:  Re: Thinning already glued guitar top?
-It's a pretty stiff 108 Carpathian spruce top. I'm thinking at least to 100. Binding might mess up the hand sanding part ?

-Scratch gauge with all the interior braces? I saw that cool magnet gauge at Stewi-Mac, but not for this guitar.
Author:  Terence Kennedy [ Sat Apr 07, 2012 6:51 pm ]
Post subject:  Re: Thinning already glued guitar top?
I thin the edges of the lower bout after the box is closed on all my builds. Gauge the thickness by looking at the edge. You could do that and then re-cut the channels. I usually wind up around .090 on the edges. .100 is pretty thin for the center unless it's a little parlor.
Author:  SixStringer [ Sat Apr 07, 2012 8:14 pm ]
Post subject:  Re: Thinning already glued guitar top?
Hmm. Well I just think that the tap-tone is not what it could be at .108-

How about using the sanding dish to 'level it out' when I'm done with it?

-So you 'radiate' the thickness from .090 to .105 or whatever? just an 'equal' gradiation? Doesnt Taylor thickness route a little .09 channel now?
Author:  Colin North [ Sun Apr 08, 2012 5:27 am ]
Post subject:  Re: Thinning already glued guitar top?
SixStringer wrote:
-
-Scratch gauge with all the interior braces? I saw that cool magnet gauge at Stewi-Mac, but not for this guitar.

Scratch block is used on the outside surface, not the inside.
It sounds like top is fitted to sides but "some" if the binding ledge is cut?
Quote:
but its almost done: Bridge,Back, binding, string it up
Bit strange - am I correct?
I suggested binding to ensure the outside edge is supported (easy to mess up the edges of binding ledge if block sanding if already cut, but you could recut binding ledges after thinning) - you are only talking about removing 0.2 mm, less than I remove from the outside of the top around the lower bout to graduate the soundboard edges after binding - with 1/4 inch depth binding I find this difference does not stand out if tapered gradually.
If you are removing thickness all over, no worries.
Anyway, good luck with the build, and I hope it turns out well.
Author:  NWflyonly [ Sun Apr 08, 2012 10:29 am ]
Post subject:  Re: Thinning already glued guitar top?
I have a similar situation with an older build/thick top but how do you handle the rosette? I assume that based on what everyone has said that you sand the perimeter crowning up to the rosette. My rosette is not set deep enough to sand the entire top so will this crowning be an issue?
Author:  Daniel Minard [ Sun Apr 08, 2012 12:51 pm ]
Post subject:  Re: Thinning already glued guitar top?
I routinely sand my tops thinner after the box is together, as a final step in tuning the top. I only sand in the area below the soundhole, so a thin rosette is not an issue.
Author:  woody b [ Sun Apr 08, 2012 6:12 pm ]
Post subject:  Re: Thinning already glued guitar top?
SixStringer wrote:
.............................................................From what I 'know' now, the top probably needs to be a bit thinner, a good bit.....................................................................................................................................


How do you now "know" the top needs to be a bit thinner? Perhaps it would be a good learning experience to finish the guitar and see how it sounds........then thin the top and see what affect that has.
Author:  SixStringer [ Sun Apr 08, 2012 6:54 pm ]
Post subject:  Re: Thinning already glued guitar top?
I could go that way, it just seems 'dull' when you tap it. I had a decent classical Yairi, and that top was 'alive' -Also, I would have the bridge glued on.
Author:  Tom West [ Sun Apr 08, 2012 7:41 pm ]
Post subject:  Re: Thinning already glued guitar top?
You have not mentioned size of guitar or said anything about the bracing. At least I don't think you have. The thicknesses you gave don't seem very heavy. May the guitar be over braced for it's size......??
Tom
Author:  SixStringer [ Sun Apr 08, 2012 8:30 pm ]
Post subject:  Re: Thinning already glued guitar top?
Its sort of a jumbo almost with X bracing.

[img][IMG]http://img854.imageshack.us/img854/3222/picture021eq.jpg[/img]

Uploaded with ImageShack.us[/img]
Author:  Terence Kennedy [ Sun Apr 08, 2012 8:53 pm ]
Post subject:  Re: Thinning already glued guitar top?
If you are already at .108 in the center based on that picture I'd say "don't just do something stand there."
Author:  SixStringer [ Sun Apr 08, 2012 9:10 pm ]
Post subject:  Re: Thinning already glued guitar top?
So just take it down a bit to the edges? I think I need to redo the Treble finger braces, I made them 'stiffer' on the bottom side by a more forward peak to the edge. I have seen video tutorials that have the guitar top wobbling pretty good, like a piece of sheet metal. That wasn't this top. Its carpathian spruce and its pretty stiff.
Author:  Terence Kennedy [ Sun Apr 08, 2012 10:30 pm ]
Post subject:  Re: Thinning already glued guitar top?
Your soundboard braces are already pretty thinned out at the edges. If this is a first or second build I'd almost say close er' up as is, finish it, and see how it sounds. Use that as a baseline on what you do on the next one.
Author:  Tom West [ Mon Apr 09, 2012 7:52 am ]
Post subject:  Re: Thinning already glued guitar top?
I concur with Terence. Box it up and finish. You may be surprised by how well it sounds. Use this as a platform to judge your working of your next guitar.

Tom
P.S. You might add a thin cap to the X joint.
Author:  SixStringer [ Mon Apr 09, 2012 9:23 am ]
Post subject:  Re: Thinning already glued guitar top?
Alright, I guess I can thin it out if I don't like it. I was basically going to reuse this, but saw a Martin seconds neck I have will fit it, and its almost done anyway. Thanks!!!
Author:  John Arnold [ Mon Apr 09, 2012 10:46 am ]
Post subject:  Re: Thinning already glued guitar top?
Quote:
it just seems 'dull' when you tap it.

If the binding ledge around the top is cut, that would explain the dull tap. It will come alive again once the binding is installed.
I haven't seen a piece of Carpathian that I would thin below 0.108" on a dreadnought.
Author:  Daniel Minard [ Mon Apr 09, 2012 1:27 pm ]
Post subject:  Re: Thinning already glued guitar top?
+1 on what John said. The bindings will make a big difference.
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