Been struggling with this for a while now.

Having a rectangular block I want to mill a groove whose bottom direction is inclined to all sides at angles A, B & C (angles measured in the planes of the sides of the block).

If I am correct the first two steps are:

With the sine vice jaws vertical clamp the block rotated in the vertical plane of A such that top surface makes angle A with the vice base plane.

Tilt in the vertical plane the sine vice jaws to angle = atan (tanB x cosA)

Now comes the part I can't figure out. I need to set the vice base at some
angle in the X - Y plane (a function of C, A and B) to the X axis of the mill. What is this function?

Help, corrections much appreciated.

John.

Cross posted to RCM.