The steps do not need to be followed in sequence and not in order of the most likely to least likely.
Pick the easiest and cheapest solutions first and work your way to the more complicated and expensive ones.
If you notice errors or can suggest additional causes and solutions, please let me know so I can edit this post and keep it complete and accurate.
1. Cause: The operator pulls the fabric during sewing. The Needle strikes the presser foot or throat plate and bends or breaks.
Solution: The fabric must not be pulled during sewing. The machine alone must feed the fabric.
2. Cause: Some portions of the fabric are too hard or too thick. The Needle bends or breaks.
Solution: Sew SLOWLY over such hard or thick portions of the fabric. If necessary, use a heavier Needle.
3. Cause: There is no material between Presser Foot and Throat Plate during sewing. The thread gets en-tangled below the Throat Plate and the Needle breaks.
Solution: Make certain that there is always material between Presser Foot and Throat Plate during sewing.
4. Cause: The Needle is held loosely in the Needle Bar.
Solution: Insert a new needle and make certain to tighten the needle clamping screw firmly.
5. Cause: The Needle is bent and strikes the Presser Foot or the feed dog.
Solution: Replace the defective Needle with a new straight Needle.
6. Cause: The Needle is too long and hits the Bobbin Case.
Solution: Replace the wrong Needle with one of correct length. (This applies mainly to users of the Singer 206, 306, 319, and 320 models that require the 206x13 needle)
7. Cause: The Needle is set too low.
Solution: Insert a new Needle and push it entirely up into the Needle Bar. If the Needle Bar is set too low, adjust it correctly.
8. Cause: The stitch hole in the Feed Dog is too small for the Needle in use.
Solution: Select a Feed Dog with a sufficiently large stitch hole. The Needle must go through the center of the stitch hole.
9. Cause: The Throat Plate is not held firmly in place. Its screws are not tightened securely. The Throat Plate shifts around and is being hit by the Needle.
Solution: Locate the Throat Plate correctly and tighten firmly the throat plate screws.
10. Cause: The Presser Foot is not attached firmly to the Presser Bar and shifts sideways. The Needle hits the Presser Foot.
Solution: Tighten firmly the Presser Foot Screw.
11. Cause: The Presser Foot is not lined up correctly in the machine and is being struck by the Needle.
Solution: Line up the Presser Foot as follows: Loosen the screw that holds the Presser Bar in position. This screw is located behind the Face Plate of the machine. Now turn the Presser Bar until the Needle goes through the center of the slot (or of the stitch hole) in the Presser Foot. Tighten firmly the above screw after this adjustment.
12. Cause: The Hinge Type Presser Foot, when installed, is worn excessively. The lower portion (plate) of the Presser Foot has too much looseness and shifts sideways, causing the Needle to strike it.
Solution: Replace the worn Presser Foot with a new one.
13. Cause: The upper thread is too heavy for the Needle in use. The Needle bends, strikes the Throat Plate or Feed Dog and breaks.
Solution: Replace the wrong Needle with a correct one, or change the size of the upper thread. Consult the Needle and Thread" chart.
14. Cause: The upper thread has knots that cannot pass through the eye of the Needle.
Solution: Replace the inferior thread with one of good quality.
15. Cause: There is not sufficient pressure on the Presser Foot while sewing heavy fabrics.
Solution: When sewing heavy fabrics, increase the pressure on the Presser Foot.
16. Cause: The user of the machine removes the fabric from underneath the Presser Foot without releasing the upper thread tension.
Solution: Every time the fabric is withdrawn from the machine, the Presser Bar must be raised to its highest position by means of the Presser Bar or knee Lifter. This will release the tension of the upper thread. The fabric must always be withdrawn AWAY from the operator.
17. Cause: The Needle is still in the fabric while the operator tries to remove the material from the machine.
Solution: The Needle must always have risen ABOVE the fabric before the material is removed from the machine.
18. Cause: Dirt in the Needle Clamp prevents the Needle from stitching straight into the fabric.
Solution: Remove all dirt from the Needle Clamp, insert a new straight Needle and tighten firmly the screw that holds the Needle.
19. Cause: The lower end of the Needle Bar is bent. The Needle, therefore, does not stitch straight into the fabric.
Solution: Remove the bent Needle Bar and replace it with a new one.
20. Cause: The Needle Bar or the Bearings of the Needle Bar are worn excessively. The Needle Bar sways sideways; the Needle strikes the Presser Foot, the Feed Dog or the Throat Plate and breaks.
Solution: Replace the worn Needle Bar or the worn Needle Bar Frame with new parts.
21. Cause: The Thread Take-up Spring (Check Spring) is not adjusted correctly. It exerts too much pull on the upper thread at the moment the Needle enters the fabric. The Needle bends, strikes the feed dog, etc. and breaks.
Solution: Adjust the Thread Take-up Spring. The loop of this spring must have finished its upward motion at the moment the Needle enters the fabric.
22. Cause: The point of the Hook is too close to the Needle.
Solution: Adjust the clearance between the Needle and the Hook by moving the Hook somewhat away from the Needle. The point of the Hook should be set as close as possible to the Needle without touching it.
Happy Hunting! Ed
Ed's Vintage Sewing Machine Shop