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I recently just posted this information into a post on here and realized that it'd might be very useful information to others who might not be interested in that particular post, so I just assumed make a new topic for it. This is a formula that I had picked up from someone and it works very well for me.

Things you need to know to determine the desired neck extension height:

Bridge height
Fingerboard thickness plus fret height
Expected settle in

There is some information on expected settle-in which is a guestimation of how much your top will move once it's under the amount of weight of the string pull. Different body styles, bracing patterns, string gauge all effect what the educated guess of the number is.

For example:

Settle in example,
25.4" scale lenght
Light gauge strings (.012"-.052")
25' Radius top
OM to Dreadnaught size body= Expected settle in, 1/16"

Some things that change the expected settle in, and by how much:

24.5" to 25" scale length -1/64"
Medium gauge strings (.013"-.056") +1/64
20' radius top -1/64"
15' radius top (Larson bros bracing) -1/32"
Small size (14.5" lower bout of smaller) -1/64"
Large size (17" Jumbo) +1/64"

So, incase anyone missed what I was getting at above, any variations from the example you either + or - the measurement that goes with it. (Another example being, if all of the specs are the same other than your guitar is a jumbo, add 1/64" to that 1/16" and you're expected settle in would be 5/64")

So there's some number examples for figuring what you'd might be looking at for settle in. Settle in is a nice thing to account for, but you might not want to go about it blindly. Before I knew this information, on my first neck reset (On my own dovetail guitar), I tried to account for settle in and added more than I should have for height. Now my guitar's neck angle is too high and I needed to make a saddle that was extremely tall, much taller than it should be for that bridge. Sure, an easy fix if I were to either reset the neck again, or put a taller bridge on it and reroute for saddle, then saddle would be regular sized.

That's a little example of my first learning experience with settle in. Also, I'd like to add that the reason that that guitar needed a neck reset is because it was the first one I had built, and I hadn't accounted for settle in. So my issue was that the action was always way too high, and my saddle was a very short one. In the winter the guitar was fine, and summer it was unplayable. Now it's vise versa! ;)

Anyhow, account for settle in or not, it's your choice, but above is the information to help account for it in a more accurate fashion.

SO NOW THE FORMULA:

So to determine your desired neck extension height (NEH, add your bridge height (BH) and settle in (SI) and then subtract the fretboard Thickness (FT)
NEH = (BH + SI) - FT

An example of the OM with a 3/8" bridge and 9/32" fretboard (1/4" fingerboard plus 1/32 for frets, don't forget the fret height!)
3/8"(BH) + 1/16" (SI) = 7/16" ; 7/16" - 9/32 (FT) = 5/32" (NEH)

The neck extension height is the measurement that you would need to measure at the bridge location without a fingerboard or bridge on the guitar.

Meaning if you're neck is on, flush with the top and you lay a straight edge onto it, you would want the neck angle to be adjusted as so you're bridge location measures you're NEH.

If there's any confusion just ask!

-Dan

Everything about building can be debatable. I'm going to stand by this, as it's worked for me, and the bracing is a pretty standard martin bracing.

This is the formula I've been using, and it's the formula I've been taught and it works.

Notice I also mentioned take the expected settle in as you will, it doesn't change the facts for the NEH formula. Leave the settle into the factor or not, I included it's an option.

-Dan

Also, the settle in is not an immediate factor. This is set up to account for anywhere from months to a couple years.

The top will move that is not a question... And if you're setting a dovetail neck, and you put a straight edge on you're full fretted ready to go neck, and the straight edge is 1/16" of an inch over the bridge, that's a pretty standard acceptable measurement. If you're straight edge is crashing into the front of the bridge, it's a different story as far as the leeway, but 1/16" over the bridge height is not a stretch.

The last neck reset I did was on a 1974 guild 12 string dread, and I understand that the guitar has 12 strings, but the bracing pattern is considerably beefier than a standard one, considering that guild even threw in a 3rd lower transverse brace, and the braces are thicker in general. Not to mention this guitar is tuned to D standard tuning.

Anyhow, when I did the neck reset on this guild, I strung it up and measured the bridge height. Then I unstrung it and measured the top with no tension. The change from string tension was 3/64", which is obviously just under 1/16". And just for giggles, my martin dread I have hanging on the wall I measured the change in bridge height from strung up to unstrung and that was 1/16".

If any thinks that the settle in being 1/16" is a load of crap, take some older (not freshly strung up) guitars and measure the difference on a few to get the feel of the change. Then adjust the measurement accordingly. I've found these to be very useful.

-Dan

Just for a bit of credibility here's a quote from Cumpiano's "Importance of String's Back-Angle" article.

http://www.cumpiano.com/Home/Newsletter ... tter3.html

"With the straightedge thus placed on the frets, its far end should just "tickle" the top of the bridge on a well settled-in, well-used guitar. On a brand-new guitar that has yet to settle in (or on a 12-string guitar, which is expected to always settle considerably under tension) the straightedge should clear the bridge by not over 1/16-inch (1.5mm). There is an exception: on new 6- and 12-string guitars which are intended to carry medium gauge strings exclusively, the straightedge should clear the bridge by 3/32" (2.5 mm). On a classic guitar, the straightedge should not clear the bridge, but rather should touch the front of the bridge about 1/16-inch BELOW the top edge of the front lip, since lower tension and higher average actions are the norm on classicals."

The new six string settle in according to Cumpiano is 1/16" and the exception is with MEDIUM gauge strings he says the settle in should be 3/32".

The formula I was taught is 1/16" and medium gauge is accounted for by adding another 1/64" which is less than Cumpiano's expected settle in.

If mines a stretch, he's stretching it further.

I'm not trying to post this to start an argument by any means. I just do not like to post things that are just pulled out of the air by myself. The information I go by are guidelines someone else has pushed and proved to work, or a thought out alteration of something that's proven workable.

-Dan

For what it's worth, Todd Stock suggested I plan on on 0.030" - 0.060" of "settle in". Here is a direct quote from Todd:

As to saddle height...you will lose between .030" and .060" of saddle height due to neck relief, body distortion, and top rise/distortion

For more detail, check out this post on the OLF:

http://www.luthiersforum.com/forum/view ... neck+angle

From that post, here is Todd's formula for string height:

The formula for string height at saddle is:

bridge thickness at saddle + height of fret plane over bridge +
added height due to string clearance - 'top rise' = string height over top at saddle

To find the added height required at the saddle for string clearance, figure on .020" at first fret and 0.090" at the 12th fret on the centerline...using similar triangles, you'll have to add about 0.080" to the height of the string at the 12th, so about .170" of added height at saddle to have a playable guitar.

Dan,

Thanks for the post. I'm struggling with this stuff right now. I watched John's video a few times, and he says he's aiming for a 3/8" at the bridge location with no fretboard on.

When I calculate for my setup, I have a BH = 0.375 (3/8"), a fretboard thickness of 0.236" and if I add in the fret thickness of 1/32" I have FT = .267. If I assume a 1/16" settle in which seems appropriate, then I'd have a BEH of approximately 0.17"...which is about 1/2 of what John was shooting for. Is that right?

Are you assuming that we're shooting for a saddle height of 1/8"? And I'm assuming we're measuring the fretboard more or less in the center?

I thought I had it, but I may have a little more work to do!

Thanks!

Tj

Your decimals somewhat confused me as far as the equation goes, I'm not able to get a calculator handy to figure those out.

I'm not saying Johns way is wrong by any means, but shooting for 3/8" (your bridge height) with out a fingerboard on means that with a fingerboard on, you're going to be 1/4" over you're bridge. That doesn't sound accurate to me, there's got to be info missing there, because well over what you should have.

You said your bridge is 3/8" and your fretboard I'm going to round to 1/4" (.250) and frets 1/32".

So we've got 12/32 - (8/32+1/32). So 12/32 (bridge height)- 9/32 (fingerboard/frets)= 3/32 + 1/16" for settle in.

So with out a fingerboard or bridge on you're guitar, just with you're neck flush to the body, you should be aiming for 5/32". If you have a fingerboard on, you add the fingerboard height to what you're shooting for which would be 5/32"+ 9/32"(fingerboard and frets)= 14/32" (bridge height+settle in).

So basically with bridge and fingerboard on, you shoot for 1/16th in over you're bridge. With bridge and fingerboard removed, you need to shoot for that same angle which is bridge - fretboard thickness.

I think if John said you're shooting for 3/8" it was most likely with the fingerboard on, because that is the bridge height. That measurement doesn't factor settle in, but not everyone does.

-Dan

Darryl, if it makes it easier at all for figuring out string height when doing the saddles, I believe it's a fairly common rule of thumb to double what ever measurement you want at the 12th fret to get your saddle height.

It helps get you close. If you string up a saddle and you're at .130" on low e and .090" at high e and you're shooting for .090-.060" Then you double that different at the saddle.

So .130"-.090"= .040" which would be about an .080" adjustment at the saddle. .090"-.060"= .030" so that'd be about a .060" adjustment at the saddle.

The first fret height I figure at the nut slots by using feeler gauges. Fret the 3rd fret and check the string height at the first fret with gauges and I expect .002"-.004". Don't let it get under .002" or you'll get buzzing. If I slot under .002" on any string, I throw the nut out and start over.

-Dan

Turner, I took a look at Johns video and he had stated he's shooting for a difference of about 1/16"-1/8" between the bridge location to the neck joint for the proper neck angle. That's very close to what your result of that equation would be, noting that settle in is factored.

-Dan