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Simple question: with a shaped, unfretted fingerboard, neck attached, using a straight edge, how high above slot?

With frets installed, I like to have the straightedge about 0.030' above the bridge surface. The frets I typically use are about 0.040" tall, so without frets, the straightedge should be 0.010' below the top of the bridge.

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John

Do u use any fall-away past 14? One I’m working on has no fall-away

No fallaway on new guitars. Depending on the situation, a small amount of fallaway may be acceptable on an old guitar after a reset.

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John

I don't think fallaways matter for this discussion, as the straightedge should just float above the fallen-away frets. I gave myself a problem by building in a ski jump, the opposite of fallaway. Made a mess of my attempts at setup until I realized what I did. Bolt-on necks are our friends.

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Peter Havriluk

I built one or two ski jumps. Discovered reason was I was bowl shaping the tone bar. Stopped doing that lol

I think it also depends on your neck attachment system and upper bout bracing and headblock design. You may get more movement with a double tenon Bourgeois type attachment than a bolt on with a glued extension and even less with a glued dovetail and extension.

If you are using a bolt on neck you can attach the neck and support the headstock and weight the upper bout with about 12lbs to mimic string tension and see how much movement you get and get a ball park idea how much clearance to shoot for.

The movement may be a little less though once the extension is glued as it can act as a brace.

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It's not what you don't know that hurts you, it's what you do know that's wrong.

Without frets you should aim for at least the height of the frets you plan on installing and possibly hair more. That way once the frets are dressed you will have some airspace.

I am with J Arnold
with the frets on I like to see about 3/32 above the bridge.

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John Hall
blues creek guitars
Authorized CF Martin Repair
Co President of ASIA
You Don't know what you don't know until you know it

I generally don't use the bridge as a reference. I tape an 1/2 inch tall piece of wood at the bridge position, which is the height of the strings above the soundboard I am looking for, and place a 3 ft straight edge from the first fret to the bridge position and measure the clearance at the 12th fret. This gives me the measurement directly, which I find less confusing. My bridges will vary in height, but I like to keep the distance from string to soundboard around an 1/2 inch.

I think it’s going to depend on bridge thickness. Without the fretboard, 3/16” or so using a 30’ top radius.


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It also does not account for the amount of deflection from string tension. That can be more than 1/16" at the bridge, or 1/32" at the 12th fret.

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John

That is true John, but neither does the other method. Some people put a weight on the upper bout to simulate string tension. That can be done with either method if one is so inclined.
Again, I use a 1/2 inch block at the bridge position, and assume I will get some "pull up" on the top, and if the final height of the strings above the sound board winds up at 7/16ths I am happy with that. I build more smaller bodied fingerstyle guitars than I do Dreads and jumbos. If it pulls up too much, I probably built it too light.

Actually, setting the straightedge measurement at 1/32" above the bridge does take the deflection into account. You can do the same with your method, but you would have to add the amount at the bridge location, or subtract half that from the measurement at the 12th fret.
Deflection can be measured on a similarly constructed guitar for reference. There is no reason to settle for a 7/16" string height at the bridge, if 1/2" is the goal.
IMHO too little deflection is a sign the guitar is overbuilt.
Putting a weight on the upper bout only accounts for neck deflection, while most of the deflection is the top pulling up.

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John

Hi John,
When I said I am happy with 7/16" I should have said - I prefer 7/16th inch. I'm not "settling". For the type of guitars I build (mostly OO and size 1) I prefer a little less torque on the bridge. I use a 1/2 inch block because I am anticipating some pull up of the top. If it goes to 7/16ths I am happy with that. If it stays at 1/2" it's not the end of the world (and could probably tolerate heavier strings)
For larger instruments I prefer slightly higher strings above the soundboard, but not much if any above 1/2 inch. Larger guitars tend to be played harder.
You are right John, putting weight on the upper bout doesn't take into account the top pulling up. Some do that to simulate string tension as I mentioned. I don't do that either.
People are free to use whatever method works for them. My objection to using a height above the bridge, is that unless the bridge height is specified (which I haven't seen in any of the posts so far - and bridge heights do vary quite a bit) then the distance from the soundboard to the strings@the bridge is indeterminate. As that is one of the more critical measurements It is good to know approximately where it should end up.

Thank you all. Very useful information!

make shims for under the straight edge at the 1st &12th frets.
these would include the fret height.
The shims should be the height you want at the nut & 12th for the stung up guitar.
This will allow you to see how tall to get your saddle from the top &help with
bridge height.

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Mike Collins