The "Carver" Stories

 Eric Pritchard built two carvers for Paul Reed Smith, first the 3D Duplicating Router and later the neck carver, pictures below. These carvers were manually operated and designed to copy a master by carving a blank piece of wood. The outside shape of the bodies and necks were already done on a shaper via special form guiding jigs that Pritchard and his staff also made. The 3D Duplicating Router initially did both bodies and necks, but after the neck carver was built it only did bodies (both front and back). Both carvers had rectilinear X-Y motions plus one or more rotary motions.

3D Duplicating Router

   Shortly after they met in 1980, Eric built the 3D Duplicating Router from a picture of the commercial 3D Duplicating Router that Paul gave him and from the shapes of the guitar bodies and necks. While the commercial 3D Duplicating Router is quite lightly built, Eric's 3D Duplicating Router is heavy duty. The 3' x 5' table is a cast iron surface plate weighing an estimated half ton, not some press board concoction. Eric then placed on the left and right edges of this table a linear ball bearing rail for the Y motion half of the X-Y motion. A 2" diameter steel X shaft spanned the distance between the bearing assembly on the left to the bearing assembly on the right. The bearings on this shaft produced the X motion. The up-down motion is actually rotary around the X shaft. Consequently the router and the stylus are connected by a router shaft that is held parallel to the X shaft. The router shaft, although mounted in ball bearings, was not used freely, but set for the particular cut so that the cutter would be at the right angle at the full depth of the cut.

   Initially the 3D Duplicating Router used standard routers. However, the bearings in the routers did not last. So Pritchard built a spindle for it and then later built a really good spindle. The last spindle used precision high-speed bearings and hardened and ground precision parts. This spindle is still in use today cutting combo cabinet parts. One of the problems with the 3D Duplicating Router was that the motor speed regulation was poor and when unloaded would exceed the maximum speed of the bearings because it was a series wound motor. So Pritchard modified the motor to accept additional field current. This gave the motor the advantages of the series wound motor at low speeds without the runaway high speeds.

Neck Carver

   Initially, the 3D Duplicating Router was equipped with both body and neck fixtures. The neck operation was to cut the critical back of the neck and to blend that portion into the headstock and the heel. However, the 3D Duplicating Router cuts were quite coarse and the neck quality depended highly upon the skill of the sanding guys. In 1987, Paul took Eric to Japan to check out CNC's and Japanese guitar factories. Although they visited several, they never saw how the Japanese managed the blend from neck to heel and neck to headstock. So on the flight back, Pritchard proposed the neck carver. The neck carver has the stylus and router moving in an X-Y motion besides the master neck and a neck blank. The master and blank were mounted to square bars that ran parallel to the X motion and rotated together. This rotary action was created by a stepping motor driving large pulleys via a timing belt. The angular relationship between the two bars was adjustable via an idler. Other idlers adjusted the belt tension. The stepping motor could rotate the bars in very small amounts. So this carver was operated by passing the stylus by the neck master and then pressing the advance button to rotate both the neck blank and the neck master slightly. Then the operator passed the stylus back along the master and repeated this operation until the back of the neck was finished.

   This machine was assembled on Pritchard's driveway in Bowie, Maryland. When Paul came over to check it out he was really happy because all it took to smooth the neck out was some 150 grit paper. It took so little sanding because the surface of the neck was about 40 flats from one side to the other, each flat being about 1/16" wide. This system was actually more efficient than today's CNC's because we were approximating the nominally circular neck with a straight line whereas a CNC cutter is a ball mill, a curvature in the wrong direction approximating the nominally circular neck. Consequently the CNC actually has to make more passes. The great advantage of the CNC is that it is stiffer and does not create nearly as much chip out which in turn can waste necks and bodies. For the bodies, the CNC's are now quite fine as well so that the sanders do not have to sand as much and consequently recreate the original design more accurately.

   The 3D Duplicating Router was in use from the early 80's, actually pre-factory, until the move from Virginia Avenue, Annapolis to Stevensville when it was returned to Eric. Later, Paul gave Eric the neck carver. Both machines were stored in Pritchard's shop until it came time to tool up for guitar amps. Then the 3D Duplicating Router was rebuilt to handle cabinet parts and the neck carver was torn apart and given an extreme metamorphous into a box joint saw. The 3D Duplicating Router modifications were only to slow up the spindle, move the motor back significantly, clean up the electric controls, and make cabinet masters. Consequently, it looks very much like the 3D Duplicating Router that produced about 50,000 guitars. The neck carver make over was much more extreme and looks quite different today because it is now an automatic box joint saw.