My Machine Skips Stitches

 This is the installment for "Skipping Stitches", one of the most common problems.   Not all steps apply to all machines (if a bobbin case latch is mentioned and you have a top-loader, skip that step).  If you have a newer, electronic machine, I can't help you if these steps don't fix the problem.
  The steps do not need to be followed in sequence and are 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.

Happy Hunting!  Ed
Ed's Vintage Sewing Machine Shop

1. Cause: The machine is not threaded correctly.
 Solution: Check whether the upper thread runs correctly from the spool of thread to the Needle.

2. Cause: The Needle is inserted incorrectly in the Needle Bar. The eye of the Needle is turned in the wrong direction.
 Solution: Insert the Needle so that its eye is at a right angle with the direction of sewing and the short groove of the Needle faces the point of the Hook.

3. Cause: The Needle is bent and does not stitch straight into the fabric.
 Solution: Replace the bent Needle with a new straight needle.

4. Cause: Lint or dirt in the Needle hole prevent the Needle from stitching straight into the' fabric.
 Solution: Remove lint and dirt from the Needle Clamp, insert a new straight Needle and tighten firmly the screw which holds the Needle.

5. Cause: The Needle is too close to the edge of the stitch hole in the Feed Dog and even strikes the edge of this hole.
 Solution: Check whether the Needle is bent. Replace a bent Needle with a new straight Needle. Check also whether the Feed Dog Screws are loose and tighten these screws firmly, if necessary.

6. Cause: The grooves in the Needle are clogged with dirt and do not permit the loop of the upper thread to form properly.
 Solution: Clean the Needle with a soft rag. Be careful not to bend the Needle.

7. Cause: The slot (or the stitch hole) in the Presser Foot is too wide (or the stitch hole is too large). This causes the rising Needle to carry the fabric with it when sewing over thin fabrics, thus preventing the loop of the upper thread to form properly.
 Solution: Replace the incorrect Presser Foot with one having a correct slot (or stitch hole).

8. Cause: If a one-piece Presser Foot is used, the foot, when sewing from thick to thin fabrics, or conversely, does not hold the fabric down firmly.
 Solution: Hold the fabric down by hand while sewing, or replace the one-piece Presser Foot with a Hinged Presser Foot.

9. Cause: The pressure of the Presser Foot upon the fabric is insufficient. The fabric is not held down firmly.
 Solution: Increase the pressure upon the fabric.

10. Cause: The Needle is too close to the edge of the slot (or of the stitch hole) in the Presser Foot.
 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.

11. Cause: The Bobbin is empty.
 Solution: Replace with a filled Bobbin.

12. Cause: The end of the lower thread, which extends from the Bobbin, is too short and cannot be carried along and brought above the Feed Dog by the upper thread.
 Solution: Pull more thread (about four to five inches) out of the Bobbin Case.

13. Cause: The upper thread is too heavy for the Needle in use.
 Solution: Replace the Needle with one of the correct size.

14. Cause: The Needle is too heavy for the thread in use. The thread has too much space in the eye of the Needle.
 Solution: Replace the Needle with one of the correct size.

15. Cause: The thickness of the upper thread is not uniform. The thread has knots or heavy and thin portions.
 Solution: Replace the inferior thread with one of uniform thickness.

16. Cause: The upper thread may be too soft and does not form a proper loop underneath the Throat Plate.
 Solution: Replace the thread with one of proper quality. Use a somewhat stiffer thread.

17. Cause: Oil on the upper thread prevents proper formation of the loop underneath the Throat Plate.
 Solution: Remove the oily portion of the thread and prevent the upper thread from getting soaked with oil. Carefully wipe oil from Needle, Throat Plate and Hook and feed dog.

18. Cause: The Thread Take-up Spring (Check Spring) is not adjusted correctly. It has too much tension or releases the upper thread too late.
 Solution: Adjust the Thread Take-up Spring. The upper thread must become loose at the moment the Needle enters the fabric.

19. Cause: The Hook is timed too early or too late in relation to the Needle. If timed too early, the loop of the upper thread is still too small to be caught and entered by the point of the Loop Taker. If too late, the loop of the upper thread is already too large and twists sideways, thereby being missed by the point of the Loop Taker.
 Solution: Make certain that the Needle is pushed all the way up into the Needle Bar. Also check whether the Needle is timed correctly in relation to the Hook. For "Timing" follow this general rule: The Needle must have risen about 3/32 of an inch from its lowest position at the moment the point of the Hook is just at the center of the rising Needle. At this moment the point of the Hook must be about 1/16 of an inch above the eye of the Needle.

20. Cause: The clearance between the Needle and the point of the Hook is too large.
 Solution: Bring the point of the Loop Taker closer to the Needle. The point of the Loop Taker should be set as close as possible to the needle without touching it.

21. Cause: The point of the Hook is blunt, damaged or broken off.
 Solution: If the point of the Hook is worn or damaged to a minor degree only, sharpen it with a fine emery stone or with fine emery cloth, then polish it with crocus cloth or on a buffing wheel. The material of the Hook must not be taken off from that side of the point that faces the Needle. If the point of the Hook is broken off or if the Hook is defective beyond repair, replace the old Hook with a new one.

22. Cause: The lower end of the Needle Bar is bent. The Needle, therefore, does not stitch straight into the fabric.
 Solution: If the machine turns easily, bring' the Needle Bar to its highest position, then tap the Needle Bar lightly with a hammer until the Needle goes through the center of the stitch hole in the Feed Dog.

23. Cause: The Needle Bar or Needle Bar Frame is badly worn. The Needle Bar is too loose in its bearings and sways sideways.
 Solution: Replace the worn Needle Bar with a new one. Replace also worn Needle Bar Frame.

24. Cause: The Needle Bar has play (lost motion) in vertical direction. This may be due to the Needle Bar linkage being badly worn.
 Solution: Replace the worn and defective parts with new ones.

25. Cause: The Throat Plate is not flat, but is slightly bent downward due to repeated dropping of the Presser.
 Solution: If facilities for repairs are available, place the old Throat Plate, top surface down, on a flat surface (surface plate) and straighten it by tapping it carefully with a hammer. If badly defective, replace the old Throat Plate with a new one.

26. Cause: The bottom surface of the Presser Foot does not rest fully (flush) upon the fabric.
 Solution: Check whether there is lint or dirt between the Presser Foot and the Presser Bar. Remove lint or dirt and tighten firmly the Presser Foot Screw. Check whether the Presser Foot rests upon the machine.  If the Presser Foot is defective, replace it with a Foot that rests with its entire bottom face upon the machine.

27. Cause: The type of fabric to be sewn makes the formation of the loop of the upper thread difficult. The fabric may also be sticky and, therefore, does not permit the proper formation of the loop of the upper thread.
 Solution: Experiment with various grades of threads and needles, until a proper stitch can be obtained. It may also be necessary to adjust the Hook in relation to the Needle in such a manner that a proper stitch can be obtained. Sometimes it will help to give a different tension to the upper thread or to the Thread Take-up Spring (Check Spring).