Cypress Pine and Red gum
In addition to basic woodturning lathe and tools.you need:-
Index plate with approximately 70 "teeth"
.Router with 90 carbide tipped router bit
.Fixture to hold router
The number of "teeth" governs the depth of the zig-zag. ie. - less teeth - larger zig-zag
more teeth - smaller zig-zag
I used a modified car flywheel and ring gear. When modified my index plate had 136 teeth which proved to be too many so I used every second tooth (ie 68 teeth) to make the bowl in the photograph above
My flywheel index plate was also modified by fitting a bush in the centre which allowed it to be screwed onto the head spindle. The chuck screwed onto the spindle after the index plate.
The fixture must hold the router in the horizontal position with the centre of the router bit at the EXACT centre height of the lathe spindle.
In addition the router must be able to slide across the lathe at right angles to the bed.
NOTE: Accuracy of both the centre height and movement across the lathe bed are critically important to the quality of the zig-zag joints.
My fixture (see photo above) is basically a steel tube mounted horizontally into a fabricated steel fixture which is clamped at right angles to the lathe bed. A second fabrication, which slides along the tube, accepts the router baseplate.
1. Hold the base of the bowl in the chuck and machine zig-zag face by moving router across the lathe bed and cutting the "vee" notch in the edge of the bowl.
2. Remove chuck complete with base of bowl from the lathe and mount faceplate onto lathe with centre section of bowl fixed to it.
NOTE: Both the centre and outer sections are premachined "cylinders" with enough material to permit final turning following assembly.
3 Machine zig-zag edge.
4 Remove centre section from face plate and replace with outer section and machine zig-zag edge.
5 Glue zig-zag edge of centre section onto base.
6 Glue zig-zag edge of outer section to combined base and centre section.
7 Finish turning bowl.