Official Luthiers Forum!

So I had some time this weekend to work on a guitar I started two years ago and was able to close up the box. After removing it from the mold it became obviously clear to me that somehow in my zest for sanding the geometry into the sides that I removed too much on the treble side of the upper bout. I did a crude measurement and I was about .1" lower on the treble side than on the bass side of the lower bout. Is this a fatal flaw in the geometry of the top? I haven't cut the dovetail yet in the heel block but I assume the neck plane will match the top. Extrapolating that to the bridge, if the bridge isn't in the same plane, depending on how the rest of the top is sanded, the bridge might have to be s little thinner on the treble side. Am I correct in my thinking? Should I scrap this build and move on?

I guess the real question is what do you all do to prevent such a thing from happening when sanding the profile into the top and flattening the upper bout area?

Thanks,
Scott

The high E's saddle height is usually a little lower than the other strings already, so I don't think you should just ignore it. But I can think of several ways to correct it:

1. Pull the top off, sand the rim some more, and glue it back on.
2. Add a shim under the fingerboard extension to correct the angle.
3. Do some creative sanding of the fingerboard thickness to produce a similar result to the shim.
4. Use a cantilevered fingerboard extension so it's entirely separate from the soundboard.

If I'm understanding the problem right, I don't see any reason to scrap the build over this. If the difference of 0.1 inch you measured was at the tips of the bouts, the amount of that difference would decrease as you move in toward the centerline and the skew between the plane of the bridge and the plane of the fretboard would be small. I would be inclined to do as you suggested and, if it's necessary, make the bridge slightly thinner toward the treble side of the bridge to make sure enough of the treble end of the saddle is exposed. That seems the simplest solution.

I don't flatten the upper bout area so someone else will have to answer your question about how to avoid this.

Nice bear claw.

_________________
Once in a while you get shown the light in the strangest of places if you look at it right - Robert Hunter

Looks ok to me. Your neck might wind up a hair crooked if you register the cut off the top like most folk do, but so what. That can be addressed by the saddle.

I've made much, much bigger mistakes and lived with them. I think this will all work itself out when you do the setup.

Not all sides are flat (lots have ripples), and they are sometimes not square to the top. Even if tops start out flat, they bulge. I'm sometimes shocked these darn things fit together at all. Yet, they do. Just be aware of the tilt when you do the setup, and I bet it won't matter much at all.

What? You mean you tuned the body on that side to enhance the trembles while maintaining a full bass and strong midrange? Are you charging more for that?

_________________
Pat

This happened on my second guitar, which is also my daily player

It's easy to do. Even though I don't realize it, I apply more pressure with my dominant hand. Now I'm very intentional when I cut that taper and also when I sand the radius into the sides with my dish. I'll do 10-20 strokes, stop, turn the body 180° and sand the same number. After every few series I'll stop and take measurements just to make things are tracking evenly. If one side is uneven, I'll apply more pressure on that side for a series or two until it evens out.

Just make it for a lefty and call it a Manzer wedge.

_________________
Ken Franklin
clumsy yet persistent
https://www.kenfranklinukulele.com

I agree with Mr. Franklin...perhaps call it a Smith (as popularized by Manzer) Treble Wedge (TM).

_________________
A constellation only takes shape when one maps the whole.
- Beth Brower

This is one advantage of using a radius dish. If I read the OP correctly, you are creating the top geometry by hand. If so, then "twist" in the top at a magnitude of 0.1" isn't a huge issue. IF you are using a radius dish and one half is lower, then it isn't an issue at all because the plane of the top is still perfectly matched to your radius dish (i.e. no twist in the top). If it had been lower on the bass side, then it would be a very minor Manzer wedge.

I'd strongly advise using radius dishes. They make the geometry of the guitar much more consistent which will allow you to dial in any neck angle issues within your first few builds.

The tilt on the fingerboard will probably less than 1/16th of an inch. If the unevenness bugs you, you could saw the problem area loose and either shim the "low places" or trim down the "high places" - however you want to see it. Binding will cover any shims you might add.

I took the original post to mean that he is sanding the rims of the upper bout flat to remove the radius from the upper bout area. Hesh wrote a tutorial on this method and the sanding of the upper bout is done on a flat board with the tail block shimmed.

http://www.luthiersforum.com/forum/viewtopic.php?f=10117&t=25931

_________________
Once in a while you get shown the light in the strangest of places if you look at it right - Robert Hunter

That's exactly what I did. Did a 28' radius on the top then flattened the the upper bout area. not sure how I did it and I thought was measuring to ensure that it was the same on both sides. Based on the opinions received, I will press on.

Just curious what you all do to ensure that this doesn't happen?

Aside from checking by measuring as you go, you can keep an eye on the amount of sanding dust on the board and make sure it builds up evenly on both sides of the upper bout as you are sanding.

_________________
Once in a while you get shown the light in the strangest of places if you look at it right - Robert Hunter

not a problem;
I've seen factory guitars from the 20s-70s like this.
No player will noticed it.

But your side grains do not match.
That I would not feel good about.
But it'll sound the same if they match or not.

Mike

_________________
Mike Collins

I am aware of the side wood. It is martin Reject wood that I picked up cheap. The guitar is more of a building exercise than a masterpiece.

Before you start any fix I would check with a sraight edge to see how you stand with neck angle. A straight edge held against the centerline of the upper bout, in the area of the fingerboard extension, should clear the top by about 3/32 - 1/8" at the saddle. If it is wrong then I would come up with a solution that would fix both. Also being mindful of keeping the centerline right.

You can also check the neck angle at the 1st and 6th string locations in the same manner to see where you stand.

_________________
Joe Beaver
Maker of Sawdust

No, shallower on the treble and deeper on the bass has already been advertised as a "Soundwedge" by David Freeman, although I suspect he did it on purpose:
http://www.timelessinstruments.com/contents/en-ca/d79_Page_79.html


Sent from my iPad using Tapatalk

How 'bout calling it an Inverse Manzer or a Double Reverse Soundwedge?

_________________
Once in a while you get shown the light in the strangest of places if you look at it right - Robert Hunter

Or just call it "close enough for government work."

How about "The Reznam"?

So, no tool will help you more than a set of dial or digital calipers. First, your basic frame has got to be relatively close. Then, use radius dish in one direction, then flip to avoid pressure bias. Measure often as u get close. No plans will help u here. You have to creep up on your desired result.

Question: are those sides supposed to be bookmatched? They don't look like it

Not bookmatched. I picked up some Martin Reject wood on a visit a few years back.

Which side is shaped incorrectly? Maybe this doesn't matter. The only real way to remove a top or back is to rout it off. Just *barely* cutting into kerfed lining. Ur picture seems to indicate problem is on back side. Guess it depends on how much u value the wood.

Treble