Truing the Backhead diameter
Here is the sequence to setup this machining operation.
The rotary table is placed on the mill bed, and the absolute X,Y of the mill DRO is set to the center of rotation. An edge finder is used with a central diameter to find the rotation center.
The X,Y table is mounted on the rotary table, and the rotation angle is adjusted to be true to the mill X,Y axes. An indicator is run along the table edge to find the true angle.
The former hold-down aluminum block is bolted to the X,Y table. An indicator is used while tightening the bolts to have the hold down true to the X,Y mill axes.
The dimensions of the aluminum block are known, along with the location of the former attachment holes. An edge finder is used to move the X,Y table so that the former mounting bolt coinciiding with the backhead diameter center is positioned at the center of rotation.
The wood former is bolted to the aluminum block. The straight former sides can be trued to the mill axes using an indicator if the straight sides are to be milled.
To true the diameter, the end mill is moved to Y=0, X=(R shape + r cutter). The rotary table can then be moved and the cutter will cut a true diameter.
The part cutting proceeds by moving the end mill cutter in towards the desired final radius, while allowing for tweak moves of the X,Y table, a few thousands in X,Y to make the cutting as even as possible on the sides of the curve.