Clark Sphere Turning Jig – setup1
Clark Sphere Turning Jig
The sphere turning jig is made to create perfectly round projects and can be used for both convex and concave shapes. Some minimal assemble is required when the system is unpacked. The 1.5 inch tall base, containing 2 high quality thrust bearings, will limit the maximum convex diameter that can be turned to the lathe swing minus 3 inches. Therefore, for example, the maximum diameter turning on a 24 inch swing lathe would be 21 inches. For convex work, the jig is fixed to the lathe bed center while perpendicular to the lathe bed using the attachment plate and screw. The bearings allow the jig to rotate. Diameter is controlled either by gross movement of the holder bar (after loosening a setscrew) or by fine movements through a lead-screw.
For concave work, the Clark Sphere Turning Jig base clamp the base parallel to the lathe bed. A very long bar can be inserted into the swivel tube. Then swivel the bar after loosening the lower setscrew on the upright. Presumably the hollowing bar from the Clark Deep Hollowing System is switched out with the 12” long holder. Now either the lower or upper setscrews are loosened to allow pivoting. A tool rest must be used to support the bar. Large diameter concave hollowing projects are possible such as platters or large bowls.
The Clark Sphere Turning Jig comes configured for the swing of your lathe with a 6” holder for a ¼” HSS cutter. The 12” long tool holder has a ¾” hole drilled 6” deep. Adaptors are available to step down to 5/8” or ½” diameter so other holders on the market can be used. The height of the cutter is adjustable. The cutting edge should be placed at spindle midline or slightly higher. Position the distance of the cutter by turning the leadscrew with a 5/8” socket mounted on a power drill for quick movement. The lowest setscrew must be released then retightened for the cut. Gross adjustment of the 12” long holder can be done by sliding the holder with that setscrew loose. During convex cutting, the setscrews and all need to be tight. Do not overtighten the setscrews. Start the cut with the rig setup with the base at 90 degrees to the lathe bed and the 12” holder parallel to the jig base. Rotate the system to cut. As the cut progresses to either end, it will cut smoother and more efficiently if the 12” long holder is rotated to be perpendicular to the lathe bed. This will require turning the lead screw to get the cutter closer to a proper position for desired diameter of cut.