This my set up for doing scarf joints. I use a drop saw, as already mentioned on here the other day.
The jig bolts to the saw table as required [using the big black turn knob] and reference pins. The neck blank is clamped to the adjustable fence and the position of the cut is referenced off of the adjusting pin at the end of the jigs. Adjustments allow for different length pegheads, Six string, twelve string, banjo or CBG, etc. Saw marks are sanded off on the belt sander.
For a neck with a separate piece fretboard.
If I"m using a 1" thick board for a neck which is actually 3/4", I turn the piece on it's side(3/4" side), draw a line across where the nut is supposed to go and measure 3" back from the nut to the heel and draw another line. Then I draw a diagonal line from the nut line at the bottom(back side of neck) to the top of other line(towards the fret board side). Cut on the line. Flip the "headstock piece" over and glue together. The result will be a scarf joint at 7 degrees. Then glueing the fretboard on top will give extra support and strength to the scarf joint.
For a neck that doesn't use a separate piece fretboard.
I do it the same way except the line goes 3" forward of the nut and tuck the headstock piece flipped and under the neck piece.
The purpose of angling the face of the headstock backwards is to get the strings to go straight from the nut to the winding posts and not have to use string trees (hold-downs).
In the spirit of no-rules, if it works you're good. the current commercial production 'standards' are the result of multiple trial-and-error to find the way that works repeatably and takes the LEAST amount of MATERIAL and LABOR on a production line.
building for yourself, go with whatever angle you think looks good....here's one extreme I found on google image search...
That would require an interesting case, JL! Probably take longer to make the case than the git!
Unless a guy built a case with hole cut out the back with a can screwed on.
Not a big market for string trees in that neck of the woods. Ha Ha.
I do 11 degrees mostly because that's what Martin guitars uses. Figure if it's good enough for them...:-) Finished top of my headstocks ends up around 5.5" from nut to end.
Here's a nice article on Wikipedia:
I have read somewhere that the cut they used was to measure 4 inches then 3 inches (total 7 inches) on the other side, mark a line and cut...... has worked for me on three builds and I am pretty happy with this angle.... The article I read said use a hand saw and a mitre box..... I am a carpenter by trade so I use a circular!