A recent project required milling a 32" concave radius. Since I have Bridgeport (not CNC) I had limited options as to how to create this radius. I could fabricate a long extended plate mounted to a rotary table, but this extension would be limited by the table travel and I would have to deal with workpiece spring and chatter.

However by tilting the vertical spindle to a predetermined setting, and using a large side tooth cutter mounted on a short stub arbor held in the spindle it is possible to machine a radius larger that the diameter of the cutter. Since the cutting edge is tilted and not in the same plane to the work surface the shorter the chord length the greater the accuracy. Whenever the chord length near equates to the cutter's diameter it will generate a radius bordering on a slight ellipse.  It therefore is important to use the largest cutter available since the chord length is only limited by the cutter's diameter.

Utilizing a 9.5 " diameter cutter to mill the 32" radius  the formula for the SINE of the angle to tilt the head is determined by the formula      9.500 /32 x 2 =.148437  The SINE of .148437 is 8 degrees 32 minutes  (angle of tilt) from vertical.