In the downstroke of reciprocating slide 1, pawls 2 and 3 engage the teeth of ratchet wheels 4 and 5, turning them through an angle corresponding to one tooth, but this angle differs for the two wheels because ratchet wheel 4 has one tooth less than wheel 5. Ratchet wheel 4 has feather key 7 which engages a keyway in feed screw 6, while the bore in ratchet wheel 5 is threaded to engage screw 6. If pawl 3 is turned out of engagement with wheel 5, the axial motion of screw 6 equals zero. If pawl 2 is turned out of engagement with wheel 4, the axial motion of screw 6 per stroke of slide 1 is proportional to the angle of rotation of wheel 5. When both pawls are in engagement, the axial feed of screw 6 is proportional to the difference in the angles of rotation of wheels 4 and 5 per slide stroke.
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