Plate cam 1 rotates about fixed axis A. Follower 2 oscillates about fixed axis B and carries roller 6 which rolls along the contour of cam 1. Head a, at the other end of follower 2, slides a long flat surface d of link 3 which turns about fixed axis C. Link 4 is connected by turning pairs E and F to link 3 and to crosspiece 5 which, in turn, is connected by turning pairs T and H to links 7 and 8. Links 7 and 5 turn about fixed axes S and N and have spherical surfaces f which slide in s lots b and c of half-nuts 9 and 10. This brings the half-nuts together or spreads them apart, engaging or disengaging rotating screw 11 which is either fed axially or has a dwell. When the half-nuts are closed, the screw is fed; when the half-nuts are open, axial motion of the screw stops. Roller 6 is held in contact with cam 1 by spring 12. The lengths of the links comply with the conditions: S͞T=N͞H, T͞F=F͞H and T͞H=S͞N.
$3193$CmL,D$