Input: pink crank that moves blue slider (carrying green rack) via sine mechanism.
Green rack has traversal motion due to cyan slider moving on violet oblique runway.
The yellow shaft translates and rotates at the same time and its two cutters trace two helixes.
Helical lead L = Pi.D/tan(β)
β: oblique angle of the violet runway.
D: pitch diameter of the yellow gear.
Disadvantage: tools contact workpiece during return stroke.