into a radial borehole 21 formed in a hub portion 22 of plate 17 and is tightened against drive shaft 11 drive shaft 11 is hollow and comprises a continuous borehole 23 in which a cylindrical pin 24 is rotatably supported and in which is disposed a torsion spring 25 cylindrical pin 24 comprises at one end a radially projecting cam 26 which extends into slot 19 of support assembly 15 and an axially extending projection 27 of small diameter which is received in a borehole 28 of matching diameter in plate 16 torsion spring 25 acts on the other end of the cylindrical pin 24 as will be more fully explained below torsion spring 25 is a helical spring with two ends 29 and 30 arranged to extend transverse to the longitudinal axis of this helical spring each end is seated in a cross slot 31 and 32 respectively formed in the adjacent end of pin 24 and in the adjacent end of a holder 33 see fig1 and 4 holder 33 is cylindrical and rotatably supported in borehole 23 of drive shaft 11 and comprises four circumferentially spaced longitudinal grooves 34 a clamping screw 35 threaded into a radial borehole 36 of drive shaft 11 engages a longitudinal groove 34 and secures holder 33 in place relative to the drive shaft 11 the fabric bender 3 is pivotably supported in slot 19 of support assembly 15 and is biased by torsion spring 25 through pin 24 in a direction away from drive shaft 11 and toward the path of arc needle 1 the bolt.