Assembling the Jig Box
The trick to milling the hexagonal sleeves round is a box-style jig. It holds the core and sleeve assembly so it can be turned underneath a router bit. On top of the box, a sliding plate guides the router back and forth along the length of the box. Although I only needed one point to turn the rolling pin under the router, I made the ends with slots at three levels so I could use the jig for other projects with different diameters. The ends (pieces 1) are cut to size and notched for the sides. To make the slots, I used a 1/4″ drill bit at the endpoints and I cut the slots at the band saw. I then cut the sides (pieces 2) to length. Assemble the jig with glue and screws, and add the clamping blocks (pieces 3).
Building the Router Slide
The router slides across the top of the jig box on a custom base. It needs to slide easily but be snug enough to not shift, spoiling the grooves during milling. I used 1/2″ Baltic birch for the base and attached a fixed fence to one side (pieces 4 and 5). To keep it snug, I attached a spring-loaded fence (piece 6) to the other side of the base. It consists of a base part with offset spacers and face strips to provide a stiff spring action, keeping the slide tracking smoothly.
To be sure that the router is properly centered, I mounted the slide on the jig box and transferred the center lines. Then I drilled the mounting holes and through hole for the router. Bore the through hole large enough so you’ll be able to see your work.
Adding the Indexing System
Rounding the hexagonal sleeve is smoother and easier with the router drawn fluidly along the length of the jig. Cutting evenly spaced grooves on the other two sleeves is impossible without an accurate indexing system. Both of these are accomplished using a threaded rod system mounted to the outside of the jig.
Fix one of the rods (piece 7) to the jig side with steel angle brackets (pieces 8). The outer hole in the bracket is drilled out to 1/4″. Set jamb nuts and washers (pieces 9 and 10) to either side of the bracket so that the threaded rod does not slide side to side. Add a cross dowel (piece 11) between the brackets to connect the slide to the indexing rod, and fabricate the small crank (pieces 12, 13 and 14) for the end. Use two nuts tightened against one another anywhere the nuts must stay tight.
Drill a hole into the bottom of the cross dowel bracket (piece 15) of the slide plate. The cross dowel fits into this hole, allowing the indexing system to move the slide back and forth.
The last pieces of the jig to add are a pair of locking cleats (pieces 16). The assembly will be mounted on a threaded rod resting in one of the slots at the ends of the jig box. You’ll fix these locking cleats in place on the jig with pairs of hex head wood screws and washers, to trap the rod in its slots.
Mounting the Rolling Pin
The second piece of threaded rod, along with two sleeve clamp discs (pieces 17), jamb nuts and washers are used to hold the rolling pin assembly in the jig for milling. Another crank handle assembly is attached to one end, then sets of jamb nuts and washers are placed at each side of the jig box ends to keep the assembly from moving back and forth. Set the rolling pin in the center of the jig box with the clamp discs and jamb nuts and tighten to keep the assembly from slipping on the threaded rod as you move on to turning it.
Rounding the Sleeves
For rounding, a standard straight cutter can be used, but there are better choices. A round-nose (or core box) bit cuts more smoothly, since the rounded end takes a shallow cut at the edge and deeper toward the center. This really reduces the possibility of tearout. Because of its round tip, the core box bit needs to be moved in small increments to leave a smooth surface behind. The best bit is a dish carving bit. It has the same smooth cutting properties as the core box, but a wide flat in the center means that the cuts overlap, leaving a very smooth finish.
With the rolling pin mounted in the jig, and the router mounted on the slide base, turn the indexing handle until the router is off the end of the sleeve. Plunge the router down and lock it. Only take a shallow cut at first. With the router running, begin slowly turning the rolling pin assembly and the indexing handle at the same time. The router will begin shaving the high spots off the hexagonal sleeve. Do not let go of the rolling pin handle, or the rotating bit will tend to spin it fairly rapidly! Keep moving the slide across the jig evenly until you reach the other end. Then lower the bit and mill back across. Continue this process just until the sleeve is round.
Cutting the Grooves
Obviously, one of the sleeves will be left as a smooth cylinder. The other two get grooved, and the indexing system allows you to cut evenly spaced grooves. The threaded rod has 20 threads per inch, so each full turn of the rod moves the router bit by 0.05″. For the narrow strips, we want 1/4″ grooves spaced 1/8″ apart. So center to center, the bit needs to move 3/8″, or 0.375″. That means 7-1⁄2 turns per groove. In order to ensure even ends, mark the center of the sleeve length, and start there. With the router unplugged, plunge the bit down to the surface of the sleeve. Now set the depth stop to 1/8″ deep.
With the router running, plunge it down slowly as you turn the rolling pin assembly. Be sure to turn the assembly so that the groove is an even depth all the way around. With the center groove done, move the bit over by turning the indexing handle 7-1⁄2 turns, and start the next groove. Work from the center to one end, then return to the center and work across the other half.
The last sleeve is grooved wider, but the process is the same. I used a 1/2″ round-nosed bit and cut no more than 3/16″ deep. Center to center, these grooves should be 5/8″ apart, or 0.625″. This works out to 12-1⁄2 turns. (In either case, you can actually just do eight or 13 turns and ignore the half, since you will be trimming the ends of the sleeves later, making the grooves even. You can use a small sander to smooth the sleeves while they’re still in the jig.