Sewing Machine Thread Is Tangling, Bunching, or Breaking
Having the thread not cooperate as intended is a problem that can lead to stress among those who sew. The good news is that thread problems usually arise from very fixable issues.
Thread Looping and Bunching
Thread looping problems that occur on the bottom side of the fabric are typically issues with the upper threading, not the bobbin threading. Looping or bunching that occurs on top of the fabric tends to a problem with the bobbin threading. For any thread issue, it's best to begin by checking that the machine is threaded properly according to the machine's specifications. If the machine was not threaded with the presser foot up, it will not have the needed tension for sewing. Also check that there is no lint or debris in the area and that moving parts are oiled. Finally, check the needle for any damage.
Thread that continually breaks may be an issue with the quality of the thread or obstructions within the machine. Inexpensive, bargain threads typically shed more lint, contain knots, and break more often than good, quality threads. Lint and knots can obstruct the thread from feeding through the machine. Also check the path the thread travels through, including the bobbin and needle, is free from burrs, nicks, or any sharp points that may cause a break or snag. Polish these areas with sand paper or steel wool. If the spool itself seems to be jamming, try changing the direction from which the spool is unwinding. Some fine threads used for embroidery may be more prone to breakage; it is best to use a specified embroidery needle for these projects.
Most sewing machines require very little altering of the tension settings or disks. However, if all other thread issues have been resolved but the problem is still reoccurring, not having proper tension may be the problem. Changing the tension can affect the timing of the machine as the pressure exerted on the upper thread and bobbin thread needs to be even; therefore, its best to review the machine's manual for tension specifications. Upper tension is user adjustable, but the setting should be in a medium range for most sewing projects. Tension problems with the bobbin threading are particularly intricate and should be repaired professionally. Using different color threads in the upper threading and bobbin is a good way to determine which area is having tension problems.....or try this link...
Six Common Sewing Machine Problems Solved