Neck angle on a new build

[buzzsawlouie]

Working on my first build and am finally at the point of the build where I have to rout a dovetail for the neck. I have my LMII neck angle jig set up and ready. The top is flat. Using the calculator from this web site (https://www.tundraman.com/Guitars/NeckAngle/index.php) the neck angle should be .3 degrees. That is the calculation with a 25 13/32 scale length, fret at body is 14, height of fingerboard at neck joint is 1/4 (not including fret) and height of bridge is 5/16. Now I am no mathematician but that seems pretty flat. Should I take into consideration any changes that will happen when under tension? Based on these calculations should my measurement at the saddle point on the LMII jig be 1/16th of an inch (difference between fret board and bridge)?

[Taylor Ham]

Your bridge is pretty thin, and several things will change the angle for the plane of the frets to meet the top of the bridge.

How tapered is your fret board? what radius does it have? is the top of your bridge radiused the same as the fret board like a Martin, or flat like a Taylor? Are you measuring along the center of the fretboard, or the edges? How tall are you frets?

If your fretboard has more radius, the edges of the wider upper end will be thinner than the edges of the nut end. This will project lower on the bridge.

If you measure in the center of a radiused fretboard to the top of the flat bridge, the bass and treble sides will be too low.

So depending on your specs and where you want to measure, you can take a second look.

The best thing about this being an underestimate is that you have more room to work with. I suspect you will need more like .5 deg.

[redir]

Depends on how you braced the top. You should expect some movement on string tension otherwise you have over braced the top. I'm not sure how anyone could accurately measure and cut .3deg into a neck to get the right angle. Personally I never measure the angle even when doing a neck reset it's all done by measurements and it's fairly simple.

To get the proper neck angle attach the *fretted neck to the guitar and lay a straight edge dead center along the fretboard so that the end of it hovers over the bridge. You want about 1/32nd inch of airspace above the bridge. That 1/32in is about how much your top will rise under string tension and then you will have about 1/8th or more inch of saddle protruding with good action at the 12th fret.

*If you fret the guitar after you join the neck, which is the way I do it, then just account for the fret height in that measurement.

[buzzsawlouie]

Fret is radiused at 16" and it appears bridge is as well (purchased from Stew Mac). The bridge is currently 3/8 thick but has an opposite curve on the bottom that i will have to sand flat to fit on top properly (thus the 5/16 estimate).

Right now I am just trying to figure out what angle, if any, to put on the LMI neck angle jig to rout the dovetail. Neck and fret is not completed yet. I would not even try to attempt to measure a .3 degree angle. So would you recommend putting the aluminum alignment bar on the jig flush to the top at the saddle point and then make micro adjustments just prior to gluing?

Thank you!

[redir]

Hopefully someone will chime in who uses the LMI jig. I don't so I cannot help.

[Fathand]

There is at least one Robert O'Brien video on the LMII site which shows how to measure this. You cannot pre-calculate it perfectly because of variables like neck flex under tension, belly up, string gauge, action preference.
You also have to take into account that the neck end of your guitar body may not be perfectly square to the top. It is easy to be out .5 or 1 degree on a first build.

The video I saw shows to measure the angle at the heel block to the top so that your fretboard extension fits to the top.

There are other adjustments to make later to make up the difference, like raising/lowering saddle or deepening the slot. Your bridge at 3/8" could still be lowered, sanding the bottom, some are only 1/4" or 6mm tall.

[rick-slo]

0.3 degrees? also 16 frets to body and height of bridge is 5/16" ???

Using that calculator with the following specs:

Scale Length Help
25.5
Fret Number Where Neck Joins Body Help
12
Height Of Fingerboard At The Neck Join Help
.25
Height Of Bridge Help (actually should be height of saddle)
.625
Increase In Top Height From Neck To Bridge Help

Therefore, the neck angle should be set at 3.923 degrees for proper string action.

[buzzsawlouie]

Thanks for the responses!

I have watched The Obrien series of instructions for the LMI jig, all I ever heard him say is he likes 3.5 mm gap from saddle point to the aluminum bar. I havn't found the video where he explains how he got to 3.5 mm (curved top vs flat top??)

Rick-slo, good point on the bridge height, I was not taking into consideration for the saddle. So given that, it gets me to a 1.77 degree neck angle.
From the calculator web site;

Measurement System
Inches

Scale Length Help
25.4
Fret Number Where Neck Joins Body Help
14
Height Of Fingerboard At The Neck Join Help
.25
Height Of Bridge Help
.60
Increase In Top Height From Neck To Bridge Help
0
With a scale length of 25.4 Inches (645.16 millimeters) and the neck joining the body at the 14th fret, the bridge should be located 11.324 Inches (287.626 millimeters) from the point of the neck join.

The string 8.89 at the bridge is 0.35 Inches (8.89 millimeters) higher than where the neck joins the body.

Therefore, the neck angle should be set at 1.77 degrees for proper string action.

At the end of the day, I guess I am not really concerned with the exact neck angle other than trying to figure out the angle to set the LMI jig (or in other words what gap should be set on the LMI jig).

Mark

[rick-slo]

Sorry, my prior calculation did not enter the right value in "Increase In Top Height From Neck To Bridge" (clicked on the ? mark on the calculation and realized it is 0 for a flattop).

Measurement System
Inches Millimeters

Scale Length Help
25.4
Fret Number Where Neck Joins Body
14
Height Of Fingerboard At The Neck Join
.25
Height Of Bridge Help
.625
Increase In Top Height From Neck To Bridge
0

New calculation 1.897 degrees

[phavriluk]

And just to provoke more agita, factor in the height (rise) of the bridge on that 25' radius domed fingerboard. That will bring the bridge up all by itself. Top ain't flat. Ever.

My hair wasn't near as gray as it is now when I started worrying about these things.

[rick-slo]

Originally Posted by phavriluk

And just to provoke more agita, factor in the height (rise) of the bridge on that 25' radius domed fingerboard. That will bring the bridge up all by itself. Top ain't flat. Ever.

My hair wasn't near as gray as it is now when I started worrying about these things.

Of course that by itself is around six thousandths of an inch. However the top will belly up some
once the strings are on tuned up. Hard to be sure how much of that will occur.

To the original poster check out the forum thread called:

https://www.acousticguitarforum.com/...d.php?t=449412

If this link expires and does not work. (they do after awhile not work) then search

"How do I determine my bridge height before the guitar is strung up ?" (use forum Google search) for
what some experienced luthiers have posted.

[buzzsawlouie]

Thank you for the responses.