Changing the stationary knife on a Singer serger should be done when the knife no longer provides a clean cut on your fabric. If your fabric edge becomes ragged or the stitches begin to look uneven or puckered, it’s time to change the knife, one of two located in the serger. The movable upper knife is not replaceable as it simply provides support to the stationary knife. For the best results, replace the stationary knife according to the user guide or installation poster that came with your specific serger model
Place your serger on a sturdy table that will give you easy access to the front of the machine. Unplug the power cord from the wall and disconnect the other end of the cord from the serger. Make sure the table is free of clutter. Have a small container available to safely dispose of your used knife.
Disengage the movable upper knife. Turn the hand wheel toward you and raise the upper knife to its highest position. Open the looper cover door, located on the front of the serger, and push the movable knife holder to the right as far as it will go. Turn the knob away from you until the knife clicks into a horizontal position.
Loosen but do not remove the stationary knife set screw, usually located below and slightly to the left of the stationary knife bar which holds the knife in place. Carefully remove the knife and place it in a small, disposable container. Even though the knife is dull, it can still cause harm if handled incorrectly.
Place a new stationary knife in the groove of the stationary knife bar holder, handling it carefully to avoid the sharp edge. Tighten the stationary knife set screw until the knife is secure. The knife should fall into a groove located on the bar.
Return the movable upper knife to its working position by pushing the movable upper knife holder to the right as far as it will go. Turn the knob up and toward you until the knife clicks into the working position. Close the looper cover door before operating the serger. Reattach the power cord.
Make sure you have a clear, clutter-free working surface.
Be sure that all power to the machine is off and disconnected before replacing the knife.