Official Luthiers Forum!

In another thread, two members (Paul and Lance) mentioned sanding, or thinning, the edges of the guitar top after binding to give the top more flexibility.

I know very, very little about this, and did nothing of the sort on my one kit build (so far). Would any of you be willing to elaborate a bit more on this?

Thanks in advance for your time.

Bill

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Eagles may soar, but weasels don't get sucked into jet engines.

I looked at a Taylor top which showed their bracing and this edge. It was only ~1 cm. Which is kind of coincidental since that's about the same width as the kerfed liner. Soooo, would it really make a noticeable difference?

Taylor doesn't actually thin at the edges, but routs a channel about 2 inches
from the edge

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

[QUOTE=terken] What I'vre tried on the last two is to sand ther edges of the lower bout after
the top was glued on but not bound. That way you can see the edge of the
spruce and measure how much you thinned. Did it improve the tone? Well I
think so but it's all so subjective. I'm going to keep doing it.
[/QUOTE]

This is the same way I do it. To check my progress, I use a set of venier calipers laid up against the edge of the soundboard wood and eyeball the thickness. I figure that, especially when I'm using a magnifier for my increasing presbyopia, I'm within a few thousandths of actual thickness. You can take down the perimeter thickness of soundboard wood pretty fast with, say, 220 grit paper and a pad, so it helps to check often and also to check for consistency.

Best,

Michael

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Live to Play, Play to Live

Thanks folks...I appreciate the input. I'll be trying this on my next build!

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Eagles may soar, but weasels don't get sucked into jet engines.

Oh, I just thought I should add something else I also do.

I have a Performax 16-32 drum sander that is not quite true across its width. If I feed a piece of 16" wide stock through the sander, it will end up being about 0.010" thinner on the outside edge.

So rather than try to correct this error, I use it to my advantage. After I've cut the top to its general outline, when I'm thicknessing it, I will flip it around so that each side of the top gets passed under the thin side of the sander. As a result, my tops are tapered from side to side, with the peak thickness being in the center.

For the classicals I build, I usually call it quits with the Performax when the center is measuring about 0.095" and the edges are reading about 0.085". Because the 80 grit paper I use on the sander leaves noticeable lines in the wood, by the time I've sanded a top down to remove the sanding lines, its thickness is down to about 0.090" in the center and 0.080" on the edges. And after the top is mounted to the sides, and all the other scraping and sanding has occured, I figure I'm down pretty close to 0.085" to 0.075" range, which for my builds seems to be just about right.

Best,

Michael

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Live to Play, Play to Live

I believe I saw this at frets.com. 3 magnets were epoxied togather in a triangle then sandpaper was attached to one face. 3 more identical magnets were glued togather with a shaft for an electric drill. The rotating magnets are inside a protective sleeve that does not rotate thereby protecting the top. The magnet assembly with sandpaper goes inside the guitar and the driving assembly goes outside. It looks like the perfect setup for voicing after building is complete.
I know that I'm not describing it well, so check it out at frets .com. He has pictures and a much better description.

Al

I just checked it out. he calls it a magnetic spin sander. Seems to me that the job could be done without removing the strings. That would be a major time saver.

AlA Peebels38895.9562037037

Harry Fleishman taught us to thin the edges of the top after the box is closed up. We'd do sort of a tapping with a fingertip along the perimeter of the lower bout. It should feel a little bit drum-like in that it should bounce your finger back a bit when you tap. Kind of hard to describe in text.

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Jonathan Kendall, Siloam Springs AR

I do mine now on purpose.
By that, I mean the first one was more or less accidental. I was routing the binding ledge, and the bit began to slip out of the collet. The potential catastrophe was stopped in time to save the guitar, but the binding ledge was now too deep.
The solution was to sand the top perimeter down to be flush with the top of the bindings. (I just had to use that particular set of bindings.) The result was my first satisfying instrument.
Ever since, I've been thinning the top around the lower bout. And, I'm happy to report, no slipped router bits since then. Like most everyone else, I use my R/O sander.
Also, this step is done before the ledge is cut, so the binding channel will be of a uniform depth.

Steve

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From Nacogdoches...the oldest town in Texas.

http://www.stephenkinnaird.com

Dana Bourgeois taps and sands to 'tune' his tops. I was able to track him once using 'glitter patterns' to see what he was doing. Basically he was tuning some of the top resonant modes so that they'd couple more effectively with the inside air, which helps produce a more 'interesting' sound. The clue is the 'kick' you feel when you tap and allow your finger tip to rest lightly on the top.

I always figure the area between the bridge and soundhole is the most critical for strength, and I'm reluctant to thin there unless I have to. On the other hand, the top back by the tail block is mostly under tension stress, with very little 'lift' from the string torque, and it can be pretty thin there. I generally thin the top toward the tail block during the building process, since it's easier then than later.

Thinning behind the bridge usually brings up bass and 'fullness'. Thinning in the 'wings' between the bridge ends and the wide part of the hips brings up treble and 'brightness'.    

I generally thin my steel string tops about 1-2cm in from edge at waist
and increase to 3-4cm on lower bout. Current build is 0.120" thinning to
0.090-.095" at edges. On some guitars Ill go a bit thicker around
bridge..depending on bridge reinforcing plate design and thickness.

Sorry about the mixed units.....its the way we have to work down this way
thansk to you guys up north.kiwigeo38896.8775810185

[QUOTE=Alan Carruth] Thinning behind the bridge usually brings up bass and 'fullness'. Thinning in the 'wings' between the bridge ends and the wide part of the hips brings up treble and 'brightness'.    [/QUOTE]
Thanks, Alan--very practical information.