Update: I haven't used this jig since 2007. Compared to a spokeshave and rasps this is a pretty slow way to go. The time save is marginal compared to the setup time. I think with a better setup with a shaper could prove to be a good tool. But as it is I don't use it at all anymore.

This is a jig I made for roughing the neck carves. The way it works is pretty simple. The cutter is a half round bit with a bearing guide that rides along the back of the thickness tapered neck.

Here is the router frame. It is essentially an overhead router base.

Here you can see the cutter head.

This is the jig that holds the neck. The blocking pivots for any headstock angle. The neck is clamped in so that the top edge of the fingerboard is parallel to the base.