Here's a good example of a luthier style CNC, it's large enough to do a neckthrough bass if desired, has vaccum capability for luthier fixtures. Extremely sturdy construction.

http://www.luthiertool.com/cnc_linear.html

It's accuracy is only .005 though.

He's probably being very modest. With the components he's using it should be possible to tune it down to .001.

- XYZ travels of around 24", 18", 6". The 18" could do archtops (?) and insides of molds. More travel is always nice, but it makes it harder to achieve good repeatability, and of course the machine is larger.

Andy and Michael, thanks for the replies and info. Students picked other projects for this year, but I'll work on this on my own as I love designing machines.

Andy, on Z travel, I was thinking the router could be mounted higher to accomodate a long tool for heels. The disad of more Z travel is more carriage mass and a higher CG of that mass, which tends to cause vibration. How much Z travel do you think is needed to not remount the router? For X&Y travel, jumbos would need 19" x 23", an 18" archtop a bit bigger, but both of those are small markets. To do the outside of molds would add 6" to each axis; I'm thinking that isn't worth it, and makes the machine much bigger.

You could also machine the neck on its side, indexing off of the truss rod slot and a pin. This requires two set ups, a left and right but could be done in one fixture, even one program that incorporates a retract and pause if you so choose. This has the advantage of shorter Z, Shorter tools and you can have the undercut in the heel region, which appears much more elegant to me, vs a straight heel.

You could also machine the neck on its side, indexing off of the truss rod slot and a pin. This requires two set ups, a left and right but could be done in one fixture, even one program that incorporates a retract and pause if you so choose. This has the advantage of shorter Z, Shorter tools and you can have the undercut in the heel region, which appears much more elegant to me, vs a straight heel.

Are there any high quality but small/cheaper CNCs out there? Like just big enough to do a bridge?

David, I don't machine necks, so this is a concept and the way I would approach it. I have successfully employed such strategies in the machining of many double sided components in the past however.
The holes on the end are for a locating pin, They match a corresponding hole in the neck and locate the neck along the length of the fixture. There are two holes to accommodate flipping the neck from one side to the other.
For clamping I would probably turn this into a vacuum fixture, but you could leave some excess material for clamping tabs if so desired.
Sorry you couldn't read the text, if you're interested I send you a file in pdf, jpeg or solidworks (or the usual interchange files) just lemme know.