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Explain more about an overlocker, why so many moving parts?
The household overlock sewing machine is the general name for overlockers, or serger, used for clothing repairs or manufacture, capable of trimming the fabric edge and making a chain stitch type of stitch, along the cleanly cut edge, which stops seam a unravelling. Overlock stitches consist of threads passing through needles and loopers. They can be made with 1, 2 or 3 needles and include the following different types of stitches: single chain-stitch, double chain-stitch, over-edge stitch, compound stitch, flat seam stitch, etc, and using 1,2,3,4 or 5 threads at the same time to produce the desired overedge or overlock stitch.
Overlockers can be complex as the diagrams below show the main componants. Each of the mechanical parts, cleverly move together, so the moving components don’t touch or bash in to each other.
Presser bar
With the presser foot attached to the lower end and the presser foot spring attached to the upper end, the presser bar applies foot pressure to the presser foot and in turn to the fabric.
Stitch length dial
The overlocker stitch length and width can be adjusted. The length of each stitch can usually be set to between 0.2mm-3mm
Differental feed adjustment
Adjusts the ration of movement between the main and sub feed dogs. It can be set to gather or stretch the material whilst being sewn.
Needle bar
A needle thread loop is formed by the needle penetrating the fabric. The needle catches the upper looper thread, which comes out of looper eye.
Upper looper
The upper looper catches the lower looper thread, which comes out of the lower looper eye, underneath the fabric. It carries the upper looper thread to the left and passes the thread to the needle.
Lower looper
The lower looper catches the needle thread loop underneath the fabric and passes the lower looper thread to the upper looper.
Thread tension dial
This set of 4 dials regulates the thread tension balance between the needle, upper looper and lower looper threads. Unlike zigzag sewing machines, overlockers are unable to make a variety of stitch patterns. Stitch variations are made via changing the tension balance between the 3 (or 4) threads and changing needle position.
Thread tension unit is also attached to the presser foot height lifter. When the foot is lifted the tensions release pressure on the threads, to assist user operation at the end of a seam.
Upper knife mechanism
Before overlocking the fabric edge, the upper knife cuts the fabric edge to an even width.
Lower knife (or fixed knife)
The lower cutting blade is fixed in position and does not move. It works in unison with the upper cutter like scissors to trim the fabric raw edge, as the feed is moving the material.
Main feed dog
Located rearward beneath the presser foot, this feed dog feeds the fabric that has been sewn. The main feed dog serves as the main control of the amount of feed.
Sub feed dog
Located in the front of the needle, this feed dog pushes the fabric toward the needle. The amount the fabric is sent can be adjusted in correlation to the amount of feed of the main feed dog.
Differential feed mechanism
This mechanism allows stretch sewing or gathering through the movement of the sub feed dog.
Feed adjusting mechanism
This mechanism sets the amount of motion of the main and sub feed dog and adjusts stitch length.
