When disks 1 and 2 rotate at equal angular velocity, the edge of movable knife 3 moves up and down along fixed guides 4, occupying positions B₁-C₁, B₂-C₂, . . . Thus the angle between the edge of the knife and the stock varies periodically. Spherical pairs are provided at points A, B, C and D. At points C and D on disks 2 and 1 the pairs are displaced by 90° from each other.
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