A zigzag stitch is a sewn pattern created by repeated angular motion. When the stitch refuses to work, it can be because of the needle position, type and condition. Alternatively, it might be because of the thread, tensioning or fabric. If you eliminate all the obvious possible causes, the problem might be connected to a computer malfunction.
Disconnect the sewing machine from the mains. Check the needle for wobble. If the needle shaft is not secure in the needle clamp, it will not be able to complete a zigzag stitch correctly. If you find the needle shaft is wobbling -- even a little -- you need to reposition it more securely. Slacken the needle clamp screw or peg. Insert the needle shaft firmly in the jaw. Retighten the screw or peg. Check you have eliminated any wobble then try sewing a zigzag stitch again.
Cleaning and maintenance procedures
Sewing machines have to be cleaned periodically to ensure operational integrity. Some -- such as the Typical GC9 series high-speed double-needle lockstitch sewing machine -- require daily cleaning. Failure to clean the scraps of thread from the rotary hook could impact on the operation of the zigzag stitch. Failure to lubricate the machine with oil via its lubrication points could also cause missed stitches, as could not replacing a bent or broken needle.
If you have inadvertently misthreaded your machine, this could cause stitches to go awry. Check the thread path of your cotton to ensure it is as it should be. Check also that the tensioning is correct. Ensure the bobbin has some thread on it. Make sure also that the bobbin does not have too much thread. In the case of the Brother S-7200C sewing machine, for example, the bobbin should be no more than four fifths full.
According to Pfaff, if the machine skips stitches it could be because you are using the wrong kind of fabric for the needle. Generally speaking, the lighter the fabric, the smaller the needle size required. Try doing a zigzag stitch on a different kind of fabric to check whether this is the root of the problem. Be aware also that some older machines may be unable to do zigzag stitches at all. In contrast, more modern machines are sometimes so sophisticated that a slight malfunction of the central processing unit can lead to a mechanical failure of this type.