Why Skipped Stitches & Thread Breakage Happen When Reverse Sewing on Industrial Lockstitch Sewing Machines
Industrial lockstitch machines are widely used in garment factories for high-speed sewing. However, many operators frequently encounter skipped stitches and thread breakage during reverse sewing (backstitching). This common fault lowers production efficiency and creates defective fabric products. Below is an analysis of the main causes and corresponding solutions.
1. Timing deviation of rotary hook (hook rotor)
The rotary hook is the core component forming lockstitch. When the machine sews forward, the hook point accurately catches the upper thread loop. During reverse sewing, the needle bar movement direction changes. If the timing between the needle and rotary hook is slightly misaligned, the hook tip cannot grab the thread loop reliably, which directly causes skipped stitches. Severe timing errors will pull the thread sharply and lead to thread breakage.
2. Improper needle and thread matching
Using thin threads with thick needles, or low-quality textured threads increases instability during reverse feeding. When the machine reverses fabric direction, extra tension acts on the thread. Threads with poor tensile strength snap easily, while mismatched needles fail to form consistent thread loops, triggering skipped stitches. Also, bent or blunt needles cannot deliver stable stitching during reverse sewing.
3. Unstable thread tension
Excessive top thread tension is a major trigger. When reverse sewing starts, the fabric feed direction reverses, and sudden resistance adds extra pulling force on the thread. Over-tightened thread cannot buffer this force, resulting in snapping. On the contrary, insufficient tension makes thread loops loose, so the rotary hook fails to catch the thread and creates skipped stitches.
4. Abnormal feeding system
Uneven movement of the feed dogs creates inconsistent fabric feeding speed between forward and reverse sewing. The fabric shifts irregularly during backstitching, distorting the thread path. Meanwhile, improper presser foot pressure will make fabric slip or jam, generating instantaneous thread pulling force and causing skipped stitches or thread breakage.
5. Damaged or rough machine parts
Scratches on the needle eye, rough thread guides, burrs on the rotary hook surface will cut the thread continuously, especially noticeable under reverse sewing load. Worn needle bar bearings and loose connecting linkages also cause needle vibration. The needle shakes while moving up and down, making loop formation unstable during reverse sewing.
Practical Improvement Suggestions
Calibrate the timing between needle bar and rotary hook strictly according to the machine manual.
Select matched needles and high-quality sewing threads; replace bent or damaged needles regularly.
Adjust top and bottom thread tension to balanced status; avoid over-tightening thread tension.
Check feed dogs and adjust presser foot pressure to guarantee smooth fabric feeding in both directions.
Polish rough parts and replace worn components to eliminate sharp edges that fray threads.
Manufacturers can optimize the transmission structure and rotary hook assembly during production. Upgraded mechanical structures effectively reduce skipped stitches and thread breakage during reverse sewing, delivering stable sewing performance for long-time industrial operation.