Official Luthiers Forum!

I'm not sure I understand the problem. Is it not giving you the desired neck angle?


Sent from my iPhone using Tapatalk

The confusion and appearance of conflict seem to me to be at least partially due to the description and techniques for three separate operations being somewhat co-mingled in the discussion. My apologies if my lack of clarity in earlier posts contributing to any of that confusion or seeming conflict.

In terms of the three operations...

Establishing the fretboard extension area angle seems to me to be independent of the other two operations, as different techniques (1.5 degree angle sanded into upper bout; flat or large radius upper transverse brace glued on flat caul, etc.) yield similar results.

The second operation - setting the milling angle using a Woolson-style jig - was the initial focus of the thread, and my sole contribution was the mention of our target value and a further adjustment where there is a tapered heel used on a curved neck block area. I'm not sure what else is necessary beyond some arithmetic to subtract fretboard thickness, fret height, and difference between fret plane and string plane height from desired string height at saddle, then adding in corrections for expected body deflection under string load and the already mentioned body shape/heel geometry value, if any. Our usual numbers for setting the jig arm's pin height for a square heeled jumbo or other large guitar are:

0.500" - 0.250" - 0.045" - 0.180" + 0.060" = 0.085"

The third operation is the final fitting of the neck to fine-tune the string height at the bridge and/or the fit of the extension on the body. Between trimming with file, chisel, and flossing with sandpaper or film, the neck fit and angles are tweaked for string height at saddle. My suggestion here was based on our practice of avoiding the use of multiple, redundant reference points (two seem to be just enough and three or more too many) by using a tool with just two reference points and one measurement point. This reduction in reference points could also be accomplished with a straight edge and constant thickness shims at those points and at the measurement point. We do enough of these measurements to make the time and materials cost spent on a dedicated tool worth the savings related to labor and elimination of measurement error, so thought it germane to the discussion.

_________________
For the times they are a changin'

- Bob Dylan

That's great. I really appreciate all the time you take to help out, Woodie.

I think Woodie completely nailed it. Thank you. And yes, you fully understood and answered my question on all points

Mike

Woodie, just so I am sure, could you please name each term?

0.500" - 0.250" - 0.045" - 0.180" + 0.060" = 0.085"

I can guess some, but I'd rather you do it.

Mike

I would be delighted to do that for you, Mr. O'Melia!



For this example, 0.500" is the desired string height at the saddle. 0.250" is the projected thickness of the fretboard AT THE SADDLE LOCATION (for our non-tapered-in thickness fretboard, 0.250"), 0.045" is our expected fret height after final dressing, 0.180" is the height difference between the fret plane and string plane at the saddle, and 0.060" is the expected amount of distortion of the top under string load (sometimes referred to as 'top rise' after the apparent effect).

I did not include an example correction for the tapered heel/curved body configuration due to the wide range of possible variations, but the correction would be added to the 0.085" value above for the final pin setting.

_________________
For the times they are a changin'

- Bob Dylan

This is very helpful, Woodie.

I just want to make sure I get what is happening here. In the manual for the Luthiertool jig it describes the target "height compensation", which is I believe what your 0.085 number describes?

Here is what I am doing so far:

Note: I'm referencing the terms in quotes that are used here: http://luthiertool.com/instructions_neck_angle_gen2.pdf

1) Set the "dial indicator arm" to the right height so the pin will hit the saddle location on the body.
2) Use the "straight edge board" to calibrate the dial indicator to 0.
3) Put the body in the edge vise and put it on the jig table.
4) Use the "thumb knobs" to do the side to side adjustment. This gets the pin to centerline of the body.
5) Use the "knurled knob" to adjust the neck angle so the dial indicator reads 0 again.

Now at this point I have the body in a position where the point of the saddle location is on the same plane as the "neck plate" on the jig. So basically everything is zeroed out.

Now, I would use the "knurled knob" to set the angle back 0.085 further, correct?

Understood that all the measurements are based on fingerboard height, fret height, etc... but I just want to confirm that I understand how this "height compensation" is added in once you get the angle back to zeroed out.

I hope that makes sense. It's hard to make sure I have the needed details for the discussion.

Brad

_________________
Insta - https://www.instagram.com/cbcguitars/
Facebook - https://www.facebook.com/cbcguitars

Yes - it appears that the height compensation would apply to a bare neck (the arm is adjusted to zero the angle dial gauge using a straightedge which represents the neck plane), so the 0.085" value would be close for the guitars we build.

_________________
For the times they are a changin'

- Bob Dylan

I should mention that we are using the Woolson neck jig in this shop, which changes the angle of the neck plane and maintains a fixed table, versus the Luthier Tools neck angle jig, which maintains a fixed neck angle and adjusts the table angle...no real difference in the outcome, but it's helpful to understand that the operating principle of the jigs vary a bit.

The illustration below from the latest rev of the building guide might be useful in thinking about the different measurement planes and how body distortion affects final string height over the top. There is a worksheet that tabulates the numbers, but we use this illustration with appropriate numbers to work through the neck setting procedure with students.

The neck plane in the illustration is what I believe is being set with adjustment to the Luthier Tools neck angle jig's table using the knurled knobs (aka, table locking knobs).

_________________
For the times they are a changin'

- Bob Dylan