My process for establishing NECK ANGLE for scratch neckbuild

[tippie53]

There is a balance to the overall string height . the bridge design should also dictate the saddle height . Drop in saddles can be a bit higher than through saddle . After over 300 neck sets I have learned a few things .
With a guitar you make you need to keep some kind of log so you can see the cause effects of your process. Guitars like martin are pretty well dialed in with the processes. How much the top rises can not always be forecast. The sweet spot for most tops is in that 1/2 inch range.
Bridge weight can be a factor but so can the plate , top thickness , and brace angle. This is why I use a deflection test so I can have as consistent top structure. Most neck angles are between 1 1/2 to 2 degrees when using a Martin style design. I have seen some tops with 25 radius that uses more angle but this can and will change the tonal quality.
Have fun with the discoveries you are going to make in building. This all ties in with the top geometry . The pitfalls of high saddles can be cracked bridges , and warped saddles. Too high string height on the top can over torque the top and this can cause instability on the top , causing bridge rotation and top belly.

[Darryl Young]

Better late than never........I guess <smile>. Here is what I've come up with to calculate Neck Extension Height based of the String Height at the Bridge (instead of the Bridge Height).

SHB - String Height at Bridge
SI - Settle-In (or Top Rise)
FT - Fretboard Thickness + Fret Height
SH - Saddle Height (or String Height Above Bridge)
NEH - Neck Extension Height

NEH = (SHB + SI) - (FT + SH)

Don't forget to add FT + SH and subtact that sum from the total of SHB + SI. Another way of writing it:

NEH = SHB + SI - FT - SH

So if you had 1/2" String Height at Bridge, 3/8" bridge, 1/8" saddle, 1/4 fretboard & 1/32 frets for an FT=9/32, and use a Settle-In of 1/16.

NEH = (SHB + SI) - (FT + SH)
NEH = (1/2+1/16) - (9/32+1/8) = 9/16-13/32= 5/32"

Note if you decide not to use a Settle-In value, then in the example above remove the 1/16" and NEH= 3/32" (about 0.094").

So on the 00 I'm building, here are the values I'm considering using:

SHB = 1/2"
SI = 0.0" (SI was negative using the SI formula Dan posted so using zero)
FT = 9/32"
SH = 0.150"

NEH calculation for my 00 body:

NEH = (SHB + SI) - (FT + SH)
NEH = (1/2" + 0) - (9/32+0.150) = 0.500 - 0.431 = 0.069"

So roughly a neck extension height of 70 thou. For a sanity check, I'll run the calculations for Fret Plane Height Above the Bridge (FPHB) which includes the Bridge Height (BH) in the calculation. First, here is a formula for String Height above the Bridge (SHB).

SHB = BH + SH + FPHB - SI (Note: BH = Bridge Height)

Now I'll solve this SHB formula for Fret Plane Height Above the Bridge (FPHB):

FPHB = (SHB + SI) - (BH + SH)
FPHB = (1/2+0) - (0.350+0.150) = 1/2-1/2=0.0"

So does it sound reasonable on my 00 body that with the neck and fretboard installed and fretted, that if I layed a straight edge on the frets that it would kiss the top of my bridge? (height of 0.0 above bridge)

Look forward to your feedback.

[tippie53]

there are 2 points for the target. what style bridge are you using? A drop in saddle belly bridge can use more saddle height than the traditional through saddle.
If you plot for .150 to .180 of saddle you will want to be about .062 above the bridge. On a traditional glued in through saddle you don't want as much saddle height , plot for about .100 . When I started building I tried these formulas , and the best results come from simplicity , a straight edge and measure the bridge / saddle height at the point of the saddle. And don't forget your center line
That is why I use the ACE system , Angle ,Centerline ,then elevation. An over set neck can bring more problems than under set. The numbers are for steel string guitars and if you are withing a .030 tolerance you will be fine .

[Darryl Young]

Interesting. I've learned a little by doing these calculations and reading the posts from Dan and John.

I noted that John recommends a straight edge on the fret plane to lay 1/16" above the bridge. I made a spreadsheet with the calculations above and as I posted above, assuming there is no top rise (or no settle in), the equations show the straight edge should lay right on the bridge. Note that if you have the saddle height equal to the string rise at the bridge (twice the 12 fret action height), this will always be the case.

So if the saddle height is equal to the string rise.......why would you ever have need/want the fret plane higher than the bridge? The answer seems to be that you are allowing for the top to rise (described as settle-in previously in this discussion). Also note that John advises 1/16" above the bridge and Dan earlier advised 1/16" of settle-in for a dreadnaught with the specs provided. I entered a Top Rise (Settle-In) value of 1/16" in my spreadsheet and sure enough, it calculated that a straight edge laying on the frets would lay 1/16" above the bridge.

Now discussing Settle-In, Dan gave some neat guidelines above that changes with body size, string gauge, etc. Since I'm using a small body (00) and short scale, it predicted a Top Rise of less than 0". Dan pointed out earlier not to use a Settle-In value less than 0". In Dan's previous thread on NEH calculations, I referenced some information from Todd Stock about calculating NEH where Todd stated to use a Top Rise in the range of 0.030" - 0.062". It's difficult to believe the top won't pull up any (and neck flex or any other contributing factor would all add up to 0). So maybe I should use a Settle-In value of the low end of Todd's suggested range (0.030") for my calculation. That would make my Neck Extension Height (NEH) equal to 0.098"......which is very close to the 0.094" I've heard/read John suggest before.

[Darryl Young]

So I'm wanting to modify the NEH formula to calculate the thickness shim to use at the bridge location so that I sand the proper angle into the rim above the soundhole. Earlier I came up with this formula based off the bridge height:

NEH = BH+RD+SI-FT (where RD = Radius Depth)

So if I add RD to the NEH formula describe above that is based on String Height at the Bridge, I get this:

NEH = (SHB + SI + RD) - (FT + SH)

So using numbers for the 00 I'm building:

NEH = (0.500 + 0.030 + 0.067) - (9/32 + 0.150) = 0.597 - 0.431 = 0.166"

So does it sound reasonable to use a shim 0.166" thick across the rim at the saddle location for sanding the neck angle into the rim up above the sound hole?

[deadedith]

I don't disagree or agree with the above; here's a sketch of how I do it. (I use a 40' radius top, standard belly bridge.)

- the cheek to fretboard surface angle is always 88.7*. That is the first thing, around which everything else must harmonize with.

- the rim at the headblock must be dead flat. When the neck is attached, that 88.7* remains unchanged.

- I slope the rim, from the front of the soundhole to the rear of the headblock, 1.3*.

- This makes for the 'straight line' principle that is the aim of the neck angle and top slope

- Close up the box (after all the bracing and other stuff, obviously :-)

Then:
-That leaves 3 variables that key off the straight line and determine the string height.
- bridge thickness
- saddle height
- top dome
-The top dome cannot really be 'adjusted' and is not always exact anyway.
-So the saddle height and bridge thickness are what we have to work with.
-Saddles are not difficult to adjust.
-When it comes to bridges, even Martin keeps 3 heights of bridges so that with the variables in the top dome and other inaccuracies they will have a bridge that works. I make a bridge that is usually very close to correctness, though it is easy enough to thin if need be and in fact I have done that. I usually tape the bridge in place while I make adjustments.

I don't think it is possible to come up with a perfect formula (but I may be wrong!), it's just important to have the straight line first, and know how to adjust the saddle and bridge to deal with the dome.

[Darryl Young]

Good points deadedith. So do you use that same angle no matter if you have a 12 neck join or 14 fret join? Since the distance from the neck block to bridge changes, seems the angle should change. Maybe it's not enough to be significant......or at least still within the range of adjustment. Also, the scale length changes the bridge position......but again, maybe it doesn't change enought to be outside the range of adjustment.

My goal is to avoid using a shorter bridge, or in other words, I want the string height at the bridge to be 1/2" if at all possible. I haven't built enough to have a feel for maintaining this so I'm doing my best to get it correct.

[deadedith]

I very seldom have to thin the bridge - in fact, only once. I use mainly 12 fret instruments and the neck angle is always the same - I see your point, but in practice the difference between 12 and 14 frets is negligible.

I will floss the cheeks a tad to make up for inconsistencies, that's about it.

For setup, I set relief first, then work on the saddle to get the right string height over the 12th fret, then work on the nut.

(BTW, credit where due, I learned most of this from a certain Ken Cierp.)