If the bottom thread of the sewing machine cannot be hooked, it is usually because the position of the needle is too high. Just lower the position of the needle properly.
1: jump stitch
1.1 Accidentally skip stitches
(1) When sewing materials with uneven thickness, because the selected needles are thinner, when encountering thicker parts of the sewing materials, the needles are prone to drift, resulting in skipped stitches. Adjustment method: replace the corresponding machine needle, and properly slow down the sewing speed when sewing materials with uneven thickness.
2) Because the inclination of the rear wall of the needle is not perpendicular to the rotary hook, the thread hooking of the rotary hook is not good. Adjustment method: Properly adjust the orthogonal position of the needle and the rotary hook. When the needle hooks the thread, the tip of the hook should be 1.55mm from the upper edge of the needle hole and 0.05mm from the groove of the needle.
(3) The quality of the suture is not good and the twist is uneven, resulting in insufficient stability of the loop formation. Adjustment method: Choose suitable sutures with good twist, and use left-twisted thread for the upper thread.
(4) When sewing thin materials, the thin sutures are sewed with thick machine needles by mistake, resulting in weak spring force of the thread take-up spring. Adjustment method: replace the machine needle and increase the tension of the thread take-up spring.
(5) The tip of the needle is fluffed or bent. Adjustment method: replace the needle.
(6) The tip of the rotary hook is fluffed and deformed after sewing for a long time. Adjustment method: Reasonably grind and polish the hook tip.
(7) When the machine is used for a long time, the needle hole of the needle plate is greatly worn, which exceeds the tolerance range of the original design. Adjustment method: replace the appropriate needle plate.
(8) The pressure of the presser foot is too weak. Adjustment method: increase the presser foot pressure.
1.2 Intermittent jumper
(1) When the machine is used for a long time, the high and low positions of the needle bar are displaced. In addition, the needle bar connecting column, needle bar connecting rod, thread take-up crank and other parts are worn, and the gap is loose, resulting in skipped needles. Adjustment method: Replace the worn parts, readjust the height position of the needle bar, the correct position and clearance of the hook and the needle according to the standard.
(2) Caused by changing different sewing materials. Adjustment method: The needle and thread must meet the requirements, and the position and gap between the rotary hook and the needle should be adjusted reasonably. When sewing thick materials, the pressure of the presser foot should be increased.
(3) The plane of the bottom of the presser foot is not close to the plane of the needle plate and the surface of the cloth feeding teeth. Adjustment method: Grind the presser foot and cloth feed dog to make the planes of the three close together or replace the presser foot and cloth feed dog.
(4) The needle is bent. Adjustment method: replace the needle.
(5) The needle is too thin or the suture is too thick. Adjustment method: replace the corresponding machine needle and suture.
1.3 Continuous skip stitch
(1) The end of the bottom thread is too short, and the thread loop cannot catch the bottom thread. Adjustment method: Take out the bobbin case and bobbin, and pull out the bottom thread by about 10mm.
(2) After long-term use of the machine needle, or improper maintenance, the position of the parts changes, and the sewing requirements cannot be met. Adjustment method: Replace the qualified parts, adjust the height position of the needle bar, the correct position and gap between the needle and the hook tip.
(3) The upper thread is melted by the needle heat. Adjustment method: Needle cooling (silicone oil) should be used for chemical fiber threads.
(4) When sewing special materials, the thread loop cannot be formed normally. Adjustment method: slow down the sewing speed and increase the smoothness of the upper thread.
(5) For automatic thread trimming machines, the upper thread end of the needle is too short after thread trimming, and the upper thread comes out of the needle hole. Adjustment method: adjust the matching time of the thread trimming cam.
(6) The presser foot groove is too wide. When the needle leaves the sewing material, the movement of the sewing material will affect the formation of the thread loop (the impact is the greatest when making thin materials). Adjustment method: move the presser foot left and right according to the sewing material, or fill the wide groove with solder, then open a narrower groove, polish or replace the presser foot.
2: Disconnected
2.1 section line
(1) The edge of the needle hole has an acute angle or the needle groove is fluffed. Adjustment method: polish the pinhole or replace the machine needle.
(2) The thread-passing parts of the upper thread are fluffed, so that the suture is blocked during movement. Adjustment method: Repair the damaged thread-passing part or apply polishing paste on the suture to polish and polish.
(3) Thin thread is used for sewing thick materials. Adjustment method: replace the suture.
(4) Suture strength is too poor. Adjustment method: replace the suture.
(5) The suture tension is too high. Adjustment method: Loosen the tension nut.
(6) The inner groove of the rotary hook has an acute angle, which will bruise or break the suture. Adjustment method: Polish the inner groove of the hook, or replace the hook.
(7) The positioning hook of the rotary hook is improperly matched with the groove of the shuttle frame. Adjustment method: Adjust the coordination of the positioning hook of the rotary hook so that the upper thread can pass through smoothly.
(8) The needle is overheated and the chemical fiber thread is fused. Adjustment method: choose the appropriate needle or thread cooling (silicone oil).
(9) There are burrs and sharp angles on the edge of the needle hole on the needle plate, which may damage the suture. Adjustment method: use sand rope or polishing paste to polish, but do not make the pinhole too large, too large will cause needle skipping.
(10) The direction of the needle is wrong. Adjustment method: Install the needle correctly.
(11) The needle is bent. Adjustment method: replace the needle.
(12) The up and down stroke of the needle bar is wrong, the thread take-up on the needle bar crank, and the crank positioning screw are not positioned in the groove of the thread take-up crank or the positioning direction is wrong. Adjustment method: Reposition, correct the wrong positioning direction.
2.2 Broken bottom line
(1) The bobbin thread is too full, too loose, and too messy, so that the bottom thread cannot go out smoothly during the sewing process, resulting in thread breakage. Adjustment method: Correct the bobbin winder to make the winding on the bobbin even, compact and neat.
(2) The bobbin is too large or the concentricity of the bobbin is not good, and the operation is not flexible. Adjustment method: adjust the coordination between bobbin case and bobbin heart.
(3) The position of the cloth feed dog is too low, and the distance between the fast mouth at the bottom of the cloth feed dog and the outlet of the bottom thread is too small, which causes friction between the bottom thread and the fast mouth at the bottom of the cloth feed dog. Adjustment method: Reasonably adjust the height of the feed dog, remove the feed dog, and polish the fast mouth at the bottom of the feed dog with fine sand.
(4) The bottom line of the rotary shuttle is worn and caused a fast mouth. Adjustment method: replace the rotary hook.
(5) The edge of the hook is fluffed and the bottom thread is broken. Adjustment method: Grind the rough edge of the rotary hook.
(6) Poor coordination between the hook and the bobbin case, resulting in poor thread tension. Adjustment method: adjust the matching gap between the rotary hook and the bobbin case to make the thread tension of the bottom thread even.
3: floating line
3.1 Floating bottom and upper line
(1) Due to the poor coordination between the feeding and the stabbing cloth, the bottom and upper threads are twisted unevenly, forming floating threads. Adjustment method: Adjust the positioning position of the eccentric wheel.
(2) If the tension of the upper thread is too high, the upper thread will float; on the contrary, if the tension of the bottom thread is too high, the bottom thread will float. Adjustment method: lower the tension of the upper thread when floating the upper thread, increase the tension of the upper thread when floating the lower thread, and adjust the tension of the lower thread.
REHOW Textile Machinery
An enterprise specializing in textile machinery manufacturing, it is committed to providing high-quality mechanical equipment and technical solutions for the global textile industry.
It mainly produces various sewing machines, high-speed looms, cloth inspection machines, cloth packaging machines and other textile equipment. We have independent research and development capabilities and a complete quality management system. All products have undergone strict quality testing and certification to ensure product stability and reliability.
Choosing rehow sewing machine deserves your peace of mind. REHOW has an efficient and professional service team, committed to providing customers with high-quality consultation and after-sales service. REHOW has always been adhering to the business philosophy of “integrity, quality, innovation, and win-win” to create a better future hand in hand with customers.
Post time: May-08-2023
