Pfaff hobbylock 794 Owner's Manual - Page 30

Changing upper knife: The upper knife is carbide tipped and will not need to be replaced with normal use. It has to be replaced only when the cutting edge has been damaged. Unplug the machine. Push the upper knife holder to the far right and turn the knob clockwise until it clicks. Unscrew the knife retaining screw and remove upper knife. To replace the upper knife, insert the retaining screw through cutout (1) of the knife. Screw it into threaded hole (2) of the knife holder. Tighten slightly and set the upper knife in the cutting position. Turn the hand wheel counterclockwise until the upper knife arm is in the lowest position. The front edge of the upper knife should be 0.5 to 1.0 mm lower in this position than the surface of the needle plate. Tighten the retaining screw securely.