At the 1997 Healdsburg festival I saw a photograph of James Olson's neck carving machine. His machine had the neck rotating on its axis as a router slid in a track along its length, carving the shaft. I liked the idea of machine-carving the neck shaft. I have had trouble at times with tendinitis in my hands, so I've always tried to let power tools do as much of the hard physical work of lutherie as possible. I also liked the idea of being able to exactly copy a given neck profile, to make the feel of my guitars more consistent. So, I designed and built this pantograph neck shaft duplicator.
The pantograph mechanism is made of 3/4" aluminum, which I machined using my bandsaw and router. (You can machine aluminum with woodworking tools, you just have to clamp really well and go slow.) The pantograph consists of two long bars which hold the neck and template, two pivot arms on each end of the bars which lock the bars together so they rotate in parallel, and a mounting block on each end. The two bars have three 1/4" bolts sticking out the ends. The middle bolt goes into a mounting block at each end which is mounted to the wooden carriage, and each of the other two bolts go into holes in the pivot arms, one arm on top, one on the bottom. The bars rotate on the axis of the middle bolts, and the pivot arms link the bars so they rotate in parallel to one another.
The bars are held a set distance apart by being bolted into the mounting blocks, and the wood carriage only allows movement front-to-back and left-to-right while keeping everything square. The guide is mounted the same distance from the router bit as the bars are from each other.
The carriage assembly consists of two frames of 3/4" x 2" finger-jointed wood which glide against each other on rails. The outer frame glides side-to-side inside of two 1-1/2" x 2-1/2" wood mounting beams which are attached to the 47" x 27" table top. The pantograph is mounted to the inner frame, which glides front-to-back within the outer frame. I got the rollers and rails from Pacific Bearing; the rollers are PAC3016M and the rails are PAC2245.
The templates are easy to make on a belt sander since there is no heel or headstock in the way. This assures that the neck contour will taper evenly with no humps or dips. I make the templates the same dimensions as the neck with the fretboard attached, and shape the necks with the fretboards glued on but not radiused. The stop discs at either end stop the bit from cutting into the heel or throat area of the neck blank. Bolts on the flat side of the templates go through the bars to attach them.
The neck is clamped on with a pair of small C-clamps, with a wedge-shaped caul at the head. The template is bolted on with T-nuts in small square blocks of plywood.
The guide is a piece of 3/4" steel pipe sanded smooth and mounted perpendicular to the table. The bit is a 3/4" HSS aluminum-cutting 2-flute spiral in a 1-1/2 hp router mounted under the table. It goes through rock maple like butter! Even highly flamed maple never chips out, and mahogany is just effortless.
My machine only does half the neck profile in a set of passes, then I have to flip the neck and template to shape the other half. This is actually an advantage for carving custom neck widths. By registering the bit against the fretboard edge on both halves, the fretboard width determines the overall neck width, so a single template can be used for many neck widths. I carve each half of the neck profile in a series of passes, rotating the neck a few degrees between each. I start at the fretboard edge and work around to the back of the neck, then flip the neck and template and repeat for the other half of the profile. It takes under 10 minutes to completely carve the shaft. By taking about 15-20 passes per half, the process leaves only tiny facets on the shaft which are easily sanded smooth with 220 grit paper.
I arrived at the dimensions given here partly because of the materials available, partly because of the size of the table I had, and partly because of my extra long necks. Feel free to adapt my dimensions to your needs.