Electric Sewing Machine Repair Manual

I. Vibration Issues in Electric Sewing Machines

1. The machine must be placed stably. The shuttle structure is key to noise and vibration levels in modern electric sewing machines. When installing the machine, screws must be tightened securely. Screws on the table should be screwed in deeply and flush with the surface.

2. When operating the machine, the user's weight should not be fully pressed on the table to prevent deformation.

 

II. Operating Issues in Electric Sewing Machines

1. Sluggish rotation of sewing head

- Analysis: Wrong oil used, especially vegetable oil. Too much dirt in shuttle race. Connecting rod screws or cone screws too tight.

- Solution: Flush with kerosene, refill with sewing machine oil. Clean shuttle race. Loosen screws to ensure clearance.

 

2. Intermittent sluggish rotation every half circle or smooth half circles

- Analysis: Thread or debris in shuttle wheel, causing violent shaking and noise. Feed dogs too high or dog clogged, hitting needle plate on upward motion.

- Solution: Clean shuttle, add little oil. Clean or lower feed dogs. Replace or realign needle bar.

 

 

3. Sewing head stuck and won't move

- Analysis: Feed dogs too far forward or back, hitting needle plate. Needle too high, hitting machine body.

- Solution: Adjust feed dog position. Realign needle, adjust needle bar height.

 

4. Noise from needle mechanism

- Analysis: Excessive wear of needle bar, needle bar bushing, connecting link etc. Loose screws in connecting link, needle bar crank.

- Solution: Replace needle bar, bushing, link etc. Re-tighten screws.

 

5. Noise from feed mechanism

- Analysis: Wear or looseness in cone screw, dogs hitting plate, loose stitch length adjustment.

- Solution: Grind or adjust cone screw. Adjust dogs. Tighten stitch adjustment screws.

 

6. Noise from shuttle mechanism

- Analysis: Excessive clearance between shuttle and race due to wear. Excessive clearance between shuttle and carrier.

- Solution: Replace shuttle and race. Adjust clearance or replace shuttle and carrier.

 

7. General noise

- Analysis: Wear of upper shaft, lower shaft and bushings, causing backlash. Lack of lubrication.

- Solution: Replace shafts and bushings, adjust clearance between shafts. Maintain and lubricate regularly.

 

III. Thread Jamming Issues

1. Dirt accumulation. (Open needle plate, remove shuttle race, shuttle, clean with cloth. Clean feed dog slots with stiff feather brush, apply oil and run machine).

2. Tension too tight or loose in sewing head. (Adjust to smooth, natural flow).

3. Shuttle race screw too tight or loose. (Simply adjust screw).

4. Other preventive measures - consistent thread sizes for top and bobbin. Follow correct threading order.

 

IV. Thread Breakage

1. Needle blunt, causing needle bar deformation. Solution: Replace needle, beginners should use #14 needle for durability.

2. Burrs on presser foot, feed dog or shuttle point. Solution: Replace immediately.

 

V. Stitch Issues

1. Floating top thread

- Analysis: Insufficient tension.

- Solution: Increase top tension.

 

2. Floating bobbin thread

- Analysis: Bobbin spring too loose.

- Solution: Tighten bobbin screw to increase tension.

 

3. Uneven stitch length

- Analysis: Insufficient presser foot pressure.

- Solution: Tighten adjusting screw.

 

4. Loopy stitches below fabric

- Analysis: Timing mismatch between feed and take-up lever.

- Solution: Adjust cam screw for coordination.

 

VI. Fabric Issues

1. Fabric puckering

- Analysis: Blunt needle, excessive bobbin tension, improper differential feed.

- Solution: Replace needle, loosen bobbin screw, adjust differential.

 

2. Fabric damage from feed dogs

- Analysis: Feed dogs too sharp, excessive foot pressure.

- Solution: Smooth feed dog points, loosen pressure adjusting screw.

 

3. Threads or fiber damage

- Analysis: Needle blunt or broken.

- Solution: Replace needle.

 

4. Fabric not feeding

- Analysis: Feed dogs too low, excessive pressure.

- Solution: Raise feed dogs, tighten adjusting screw.

 

5. Fabric moving back and forth

- Analysis: Feed dogs too high.

- Solution: Adjust feed dogs.

 

6. Fabric won't feed backward

- Analysis: Feed cam misaligned.

- Solution: Adjust feed cam position.

 

7. Fabric feeding unevenly

- Analysis: Crooked or loose feed dogs.

- Solution: Realign and tighten feed dog screws.

 

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