How To Troubleshoot Common Faults in Heavy Duty Compound Feed Flat Bed Sewing Machine?

Heavy duty compound feed flat bed sewing machine is a multi-purpose flat sewing machine. Its most prominent feature is the use of a large rotary hook for thread hooking, combined top and bottom feeding mechanism, and alternating presser foot lifting mechanism. Due to its strong sewing capacity for thick materials, good layer sewing performance, and stable forward and reverse stitches, it is widely used for medium-thick materials such as leather and canvas.

The following are common troubleshooting steps for this machine:

I. Needle Position.

When the needle descends to its lowest position, the center of the needle hole should be aligned with the inner circumference of the rotary hook. If the fabric is thick, the center of the needle hole can be lowered by approximately 0.5 mm.

II. Synchronization of Needle and Rotary Hook.

The standard synchronization relationship is as follows: After the needle moves down to its lowest position, it rises back up 2.5 mm. At this point, the tip of the rotary hook should be aligned with the center line of the needle. In this position, the tip of the rotary hook should be approximately 1.2–1.5 mm higher than the upper edge of the needle hole. Furthermore, the gap between the bottom of the needle notch and the tip of the rotary hook should be between 0 and 0.05 mm.

III. Feed Dog Position.

① The standard position is when the feed rate is adjusted to its maximum, and the front end of the feed dog is close to the front side of the needle plate groove. The gap between the front end of the feed dog and the front side of the needle plate groove should be 1.5 mm. After adjustment, adjust the feed rate to the desired position.

② When the feed dog reaches its highest point, it should be 0.8–1.2 mm higher than the needle plate. For thicker materials, it can be adjusted up by about 1.5 mm. The feed dog is generally horizontal; it should be adjusted if the sewing conditions require an incline.

IV. Synchronization of Feeding.

The standard position is when the feed dog is flush with the needle plate, the needle tip should also be flush with the needle plate surface. If the material is thin, the needle tip can be slightly lower than the needle plate by about 0.5 mm.

V. Adjustment of the Upper Feed Mechanism.

Generally, the upper feed should be synchronized with the lower feed. However, special situations often arise in actual sewing. Appropriate adjustments should be made according to the different friction coefficients of various materials and the sewing process requirements. Specifically, the center distance between the presser foot slider and the presser foot shaft of the upper feed mechanism should be adjusted. Increasing the center distance increases the upper feed amount; decreasing the center distance decreases the upper feed amount. In addition, in actual operation, the upper feeding time can be adjusted to be slightly slower than the lower feeding time according to special requirements.

VI. Adjustment of the presser foot cross-lifting mechanism.

When sewing medium-thick materials, the lifting amount of the swing presser foot is within 5.5 mm, and the lifting amount of the small presser foot is about 3.5 mm. With other mechanisms unchanged, the sum of the lifting amounts of the two presser feet is a fixed value, but the total lifting amount of the swing presser foot and the small presser foot can be changed by adjusting the center distance between the eccentric wheel connecting rod screw and the presser foot lifting shaft. A smaller center distance increases the lifting amount of the swing presser foot and the small presser foot; conversely, a larger center distance decreases the lifting amount.

Note: After adjustment, the upper wheel should be rotated slowly to check for any collisions. It can only be used after everything is normal. The front-to-back gap between the swing presser foot and the presser foot is generally maintained at about 1.5 mm, but when sewing with a large stitch length, the front-to-back travel of the swing presser foot is larger, and vice versa. Therefore, in actual operation, appropriate adjustments should be made according to the sewing stitch length.

If you need to purchase a high-quality flatbed sewing machine, or would like to inquire for more information, please feel free to contact KINGMAX.