Overlock
Overlock is a sewing method using an overlock machine that overcasts the edge with sewing thread while trimming the fabric edge to prevent fraying and, when necessary, joins pieces of fabric together.
Contents6 sections
Definition and Overview
Overlock is a sewing method that uses a serger to cross multiple threads with a part called a looper, sewing so that the fabric edge is wrapped. In many cases, excess seam allowance can be cut at the same time as sewing, so it is used for edge finishing and joining knit products.
“Overlock” refers not only to the type of stitch, but also to the serger itself that makes that stitch. When placing an order, it is important to clarify the sewing location and the required finish rather than the machine name.
Process in Product Making
In general, after cutting, it is done for each part as edge finishing of the seam allowance or as joining of parts. In knit products such as T-shirts, cut-and-sew items, and underwear, it is incorporated into the main assembly process as a stitch that easily accommodates stretch.
For woven fabrics, it is often specified to use overlock as fray prevention at the edge of the seam allowance after the side seams or inseams are sewn together with lockstitch. However, in lined products or constructions such as French seams, where the seam allowance is hidden inside, it may be unnecessary.
- Planning and pattern design: assume the fabric thickness, stretch, and seam allowance width.
- Cutting: check cutting accuracy and prevent insufficient or excessive seam allowance.
- Sewing: perform test stitching and adjust thread tension, feed amount, and overedge width.
- Inspection: check for skipped stitches, thread breaks, excessive cutting into the seam allowance, and puckering.
How to Proceed and Practical Points
In the specification sheet, state the parts to be overlocked, whether it is joining or edge finishing, the appearance on the front and back sides, and the seam allowance treatment. If you simply instruct “lock finish,” differences may arise in how the finish is interpreted, so attach a sewing sample or cross-sectional drawing if necessary.
Set the thread, needle, and differential feed to match the textile. Differential feed is a function that changes the amount of front and back feeding, and is adjusted to suppress waviness in stretchy knits or puckering in fabrics with little stretch. Thin fabrics, stretch fabrics, and fabrics with a lot of nap require especially careful advance checking.
Because this process involves trimming off the seam allowance, restitching is limited. Confirm in advance the seam allowance width on the pattern, whether pattern matching is necessary, and whether later dimensional correction will be needed, and evaluate the stitch and post-wash condition with samples before mass production.
Ordering and Quality Notes
When requesting a sewing factory, prepare fabric swatches, a sewing specification sheet, patterns, and samples if needed. It is difficult to judge sewing suitability from the material name alone, so share the fabric stretch, thickness, surface slipperiness, and tendency for edge fraying as well.
For quality checks, confirm whether the stitch sufficiently wraps the fabric edge, whether there are skipped stitches, and whether there is puckering or loop protrusion due to uneven thread tension. Also check whether the stitch will split during wear or washing, and whether thread breakage occurs in stretch areas.
Differences from Similar Terms
Lockstitch is a representative sewing method that uses an upper thread and a lower thread, and is mainly used for straight seams. Overlock is characterized by a structure that wraps the fabric edge, and differs in that it can serve both as edge finishing and joining.
Coverstitch is a general term for stitches that use a looper and is also used for sewing that takes advantage of stretch. Overlock is a sewing method that uses the structure of coverstitch while placing emphasis on wrapping the fabric edge. Depending on the application, the two are used together.
Frequently Asked Questions
Do overlock and serger mean the same thing?
In practice, they are often used almost synonymously, but overlock basically refers to the stitch or sewing method that wraps the fabric edge, while a serger refers to the sewing machine that performs it. When requesting work, listing the target part and the purpose of the stitch helps reduce misunderstandings.
Is overlock necessary for woven fabrics too?
Woven fabrics tend to fray at the cut edge, so overlock is often used as edge finishing for the seam allowance. However, in methods such as French seams, piping finish, or constructions that cover the seam allowance with lining, another finishing method may be chosen.
What defects are likely to occur with overlock?
Typical defects include puckering and loose loops due to incorrect thread tension, skipped stitches, open seams, overcut seam allowance, and waviness in stretch fabrics. Before mass production, perform test stitching on the actual textile and check the stitch after washing and during stretching as well.
