Bed Slide-the flat plate or plates at the left of the bed which may be opened to give access to the shuttle or bobbin case and other parts of the lower stitch forming mechanism.

Bobbin-the metal spool on which thread is wound to furnish the lower or shuttle thread supply.

Shuttle or Bobbin Case-the container in which the bobbin is placed and around which the loop of the needle thread is passed in forming the lock stitch.

Rotary or Oscillating Hook- the part which enters a loop of needle thread and carries it around the bobbin case. In the long-bobbin machine this function is performed by the shuttle, which also acts as a bobbin case.

Lower Tension-the spring on the shuttle or bobbin case which controls the delivery of thread from the bobbin.

The Necessity For Proper Tensions

The tensions on the sewing machine must be adjusted to suit various fabrics. There are two tensions, the upper and the lower. The upper tension controls the thread from the needle, while the lower tension controls the thread from the shuttle or bobbin case.

The definition of the word tension as given in the dictionary is : "stress by pulling." It is the pulling of the threads together that completes a stitch on the sewing machine. After the needle thread passes around the shuttle, the upper thread is pulled by the take-up lever to take up the slack and complete the stitch by locking both threads together. If both are under proper tension, the lock occurs in the centre of the material being sewn and a perfect stitch is formed.

Proper Needle And Thread Important

A perfect stitch can be obtained when the thread is selected to suit the fabric which is to be stitched and the needle is the correct size for the thread. If the needle is too fine for the thread and the material to be sewn it is quite likely to break when crossing a seam. If a large needle is used on fine material the perforations made by the needle will show on the finished work.

Testing A Needle

An important essential for good work is that the needle be perfectly straight.

A straight needle can be determined by placing the flat side of the needle on the slide plate of the machine or any other perfectly flat solid surface. Hold the needle flat to the plate and the plate up to the light and look through. A straight needle will shown an even amount of light under it and the point will be in line with the shank, while a crooked or bent needle will show closer to the plate or further from it at the point.

Causes of Upper Thread Breaking.

-Machine improperly threaded.

Tensions too tight.

Needle bent or having blunt point.

Thread too coarse for size of needle.

Needle too fine for size of thread and material to be sewn.

Burr on needle hole in throat plate (caused by breaking needle in pulling material from machine).

Burr on needle hole in presser foot (caused by sewing over pins or breaking needle).

Needle set with flat side to outside of clamp

Needle too long for machine, or not all the way up in clamp.

Take-up spring bent or broken.

Tension disc worn so that thread works in groove.

Causes of Lower Thread Breaking.

-Improper threading of bobbin case or shuttle.

Tension too tight.

Thread wound unevenly on bobbin or bobbin wound too full.

Spring on bobbin case or shuttle worn to sharp groove.

Burr on under side of throat plate (sometimes caused by breaking needle).

To Avoid Breaking Needles

Do not sew heavv seams with a needle too fine.

Use proper size of needle for thread and material to be sewn.

See that the presser foot or attachments are securely fastened to the bar and that the needle goes through the centre of the hole.

Do not pull the material to one side when taking it from the machine. The needle may become bent and strike the side of the hole when starting to sew.

Do not pull material when sewing. The needle may become bent and strike the back of the needle hole.

Do not bend the needle when pulling out the material before cutting thread.

Do not use a needle that is too long. It is liable to come in contact with the bobbin case and break, probably spoiling the case and requiring replacement.

Do not leave pins in the material after basting and sew over them with the machine.

Skipping Stitches

Needle not accurately set into the needle bar, blunt or bent.

Needle too small for the thread used.

Needle too short for the machine.

Stitches Looping

Looped stitches are usually caused by an improper tension. If the loop is on the upper side, it may be corrected by tightening the under tension. If the loop occurs on the under side, it may usually be corrected by tightening the upper tension.

See that both the upper and lower threading are correct, that the thread is of good quality and the correct size for the needle.

Test both tensions and stitch on the same material to be sewn.

Looping of stitches is sometimes caused by the placing of the bobbin in the bobbin case or shuttle so that the thread pulls from the wrong side pf the bobbin, or by the bobbin being wound too full.

Machine Not Feeding Properly

Improper feeding is often due to the pressure being too light for the material to be sewn.

The feed dog may be worn smooth. This may be determined by running the finger over the teeth. If they are not sharp, the feed dog should be replaced by a competent mechanic.