Lockstitch

Definition and Overview

Lockstitch is a sewing method in which the upper thread that passes through the needle and the lower thread wound on the bobbin are interlocked near the center of the textile. The stitches look relatively neat on both the front and back, and it is used mainly for straight stitching in the assembly of apparel, bags, and other items.

In the sewing process, it is used for construction stitching to join cut hardware at the seam allowance, topstitching, pocket attachment, and more. Combined with the sewing sequence, seam allowance finishing, and pressing open or pressing to one side, it creates the product’s shape and strength.

Position in Product Making

Lockstitch is a basic process for assembling each cut hardware after cutting based on the pattern and specifications. It controls seam allowance width, backstitching at the start and end of stitching, and stitch position, and connects to later processes such as pressing, attaching accessories, and inspection.

In process design, confirm the thickness, stretch, number of layers, and whether curves are present. Because thin materials may cause seam shrinkage or puckering, and thick materials may cause skipped stitches or thread breakage at stepped sections, conditions are determined through test sewing.

How to Proceed and Practical Points

When placing an order, clearly state for each stitching area that lockstitch is required, along with the seam allowance width, how the stitch should look, thread color, and whether backstitching is required in the specification sheet or sewing instructions. For topstitches visible on the front, indicating the position and distance from the edge helps prevent misunderstandings.

Before mass production, test sew using the actual outer fabric, secondary materials, interfacing, and thread. It is important to match thread tension, needle, presser foot, and feed amount to the fabric, and check the front and back of the stitch, seam shrinkage, skipped stitching, and stitch elongation.

• Align the sewing direction with the grain and check for twisting or waviness.
• At intersections or stepped areas where thickness changes, check for needle breakage, skipped stitches, and stitch misalignment.
• For stretch materials, confirm whether the stitch will break during wear.

Quality and Ordering Notes

Lockstitch tends to produce stable stitches, but if the thread tension is improper, the upper or lower thread may be pulled to the surface, affecting appearance and strength. Stitch distortion, puckering, skipped stitches, thread breakage, and seam slippage are subject to visual inspection and, when necessary, strength verification.

Lockstitch alone cannot prevent fraying at the cut edge, so in areas that require seam allowance finishing, overlock or similar methods are used together. Also, for highly stretchable fabrics such as cut-and-sew knits, chain stitch may be selected depending on the application.

Differences from Similar Terms

Chain stitch is a sewing method that uses a looper to interlink thread in a chain. Because it is easier to achieve stretch than with lockstitch, it is used for knit hems and joining seams, but if the thread end comes undone, the stitch line may unravel continuously.

Overlock is a sewing method that joins pieces while wrapping the cut edge with multiple threads, or that prevents fraying. The difference from lockstitch is that lockstitch mainly serves to join hardware, while overlock is suited to finishing cut edges or sewing stretch materials.

Frequently Asked Questions

How do you choose between lockstitch and chain stitch?

In general, lockstitch is used for construction stitching on woven fabrics or areas where shape stability is desired. Chain stitch may be chosen for joining knit fabrics that need stretch or for hemming. The choice is determined by test sewing based on fabric stretch, the strength required of the stitch, and the design.

How do you prevent puckering with lockstitch?

Puckering is more likely to occur when the thread is too thick for the outer fabric, the thread tension is too strong, or the feed amount does not match. Review the combination of fabric, thread, and needle, adjust the thread tension and presser foot pressure, and then test sew under the same conditions as mass production.

Does the seam allowance for lockstitch need overlock?

Because lockstitch does not wrap the cut edge, seam allowance finishing is often considered separately for woven fabrics that fray easily. In addition to overlock, methods such as flat-felled seams and French seams are available. Choose according to the fabric properties, feel against the skin, thickness, and washing durability.