Slider 3 of slider-crank linkage ABC reciprocates along fixed guides a-a. Crank 1 rotates about fixed axis A and is connected by turning pair E to link 4 which, in turn, is connected by turning pair D to link 5. When crank 1 rotates about axis A, slider 3, to which the needle is at tached, reciprocates. At this, point F of connecting rod 4 describes the curve shown in the drawing. This curve is used for threading.
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