Hey! I finally am back to work on this project! I was able to do some work on the neck this weekend. (I copied this post from a post I just made over on Project Guitar.com
First thing I ran into was a problem The angle of my scarf joint was 2 deg more than my cad model. To fix this I set the neck up at the correct angle and milled the face of the headstock flat. angle fix
While I had the neck at this angle anyway, I decided to cut the shape of the head stock headstock shape
Then I set the neck blank up in the flat postion and cut the truss rod channel and I drilled two 1/8" locator holes that will locate the fretboard. The holes are drilled at the 12th fret marker postion and will be covered by the inlay. Locator holes and truss rod channel
Next I made a steel jig to hold the neck when I flip it over to cut the back side. The jig is a piece of 1.5 x 1.5 inch cold roll steel. On the top of the jig I milled a 1/8" tall "key" that fits into the trussrod slot of the neck. This jig give me the location for the rest of my operations. neck jig
If you look at the Benedetto book (archtop jazz guitars) he doesn't use a scarf joint. Just cuts 3 to 5 side profiles, glues them up into a laminate stack and then carves the neck and headstock from there
By using the scarf joint you avoid having end grain runout on the face of the head stock. I'm sure if Benedetto is doing it, it works and it works well. I just didn't have the material to pursue that kind of a build up.
I know all about endgrain runout (especially in the places where it can be most detrimental). Actually he buys cheep slabcut maply for the necks. Cuts out the side profile. Then when their laminated you end up with nicely quartered wood with the growth rings going in the right direction. In the end this actually cuts the material cost way down for future instruments you may wish to build.
I agree with you though that making a scarf joint eliminates the runout problem and actually makes for a stronger neck joint. I used to use them myself. But he claims he has never had a problem with either strength or runout. He also uses .7mm veneer on the front and back of the head which covers any runout so it isn't seen by the customer.
The only thing I wouldn't use this for is on a classical guitar.
This is the file I ment to attach earlier for my profile for a archtop neck.
The neck looks great. You may want to consider a locating pin in the truss rod channel down towards the nut end of the neck. 3 pins will be more reliable than 2 next to each other. The glue tends to be slippery when you glue on the fingerboard, and clamping pressure may cause it to move out of alignment. I do something similar, only I use finish nails with their heads cut off. I'm starting my first parlor guitar and I'm using up some left over scrap from other guitar projects. I just glued up a stacked heel for a bolt on mahogany neck with a scarfed on peghead.
that looks great, nice work. I've always wondered how the frets are laid out - hopefully you'll get up with the description & pics as it moves along. I know just the tiniest bit of music theory, ie Pythagorean vs tempered scales, and had always thought it must be one very difficult task to lay the frets out accurately. Or maybe its more forgiving than I'm thinking? either way, I'd guess cnc makes the job a lot easier.
Honestly, I bought my fretboard with the slots precut from Stewart- Mac Donald. If you search online there are several different fret spacing calculators available. You typically enter your scale length (distance from the nut to the bridge), and the number of frets you want, and the calculator will spit out the exact distance between each fret.