position and several positions of thread extraction application_number US 68643000 A description the single double thread chain stitch sewing machine seen in fig1 comprises a housing 1 which substantially consists of a so called base plate 2 a standard 3 and an upper arm 4 an arm shaft 5 is rotatably run in the arm 4 and can be driven in rotation by means of a driving motor 6 via a belt drive 7 mounted in the arm 4 in bearings 9 10 is a substantially vertical and hollow needle bar 8 which can be driven to reciprocate by the arm shaft 5 via a crank drive 11 at its lower end the needle bar 8 is provided with a needle 5 underneath the needle bar 8 a hook bearing 13 which comprises two commercial chain stitch hooks only roughly outlined in fig4 known for example from u s pat no 1 372 473 is mounted in bearings 15 16 for rotation by approximately 400 u00b0 about a vertical pivot axis 17 which extends in the z direction actuation of the hooks takes place via a driving connection 14 derived from the driving motor 6 rotary actuation of the hook bearing 13 takes place via two belt drives 19 20 by means of a stepper motor which serves as a pivot drive 18 the needle bar 8 is mounted in the bearings 9 10 not only for displacement in the longitudinal direction but also for rotation about a pivot axis 17 it is driven synchronously and equiangularly relative to the hook bearing 13 by the pivot drive 18 via a setting shaft 21 which is drivable by the belt drive 19 and extends in.