Radius Setup Jig

This jig is used to set the imaginary radius center of the material to be radiused at the center of the rotary table. It is also used to repeat a setup when several same dimension radii need to be made. As so often happens, the need is the catalyst for these kinds of projects. I had been thinking about this problem on and off for the last couple of years, but there was never a real need to drive me to get on with a design. My lathe ball turner project provided the need, as it had several identical radii on two of it's top slide parts. The jig requires a centering pin in the rotary table for it's initial mounting.

Begin by mounting the rotary table and accurately centering it under the mill spindle. The slide portion of the jig is preset to provide room to access the T-nut screw and provide enough additional adjustment to set the desired radius. My center pin is .500" diameter, so the initial mounting would be suitable for a .25" radius. The sliding portion of the jig is adjusted to the desired radius by moving it a measured distance from the initial setting. The center pin is then removed and the material to be radiused is placed on suitable packing (you don't want to cut into your rotary table!) and clamped in place against the 90 degree V of the jig. Once the material is securely clamped, the jig is removed. The rotary table can now be offset in one axis (X or Y) by the desired radius PLUS the radius of the milling cutter. If the material to be removed is more than you can cut on one pass, adjust the same axis an additional amount and work your way back to the final offset, cutting .020" or .030" per pass. Each pass is completed by turning the rotary table back and forth 90 degrees. The final pass should have the radius blending into the straight edges of the material.

Now, to setup for the next identical radius, mount the jig back on the table pressing against the just completed material still clamped in place. Lock the T-nut screw. Now remove the material and reposition for another corner or choose the next piece of material to be radiused. Clamp the material securely, remove the jig, and cut the radius as before. Minimal setup time for all succesive parts with the same radius!

As may already be obvious, the sliding part of the jig with the 90 degree V is only suitable for radiusing a 90 degree corner. Plates with other degree angles may be made to suit. A design of the top plate with adjustable angles may also be possible.