CHAPTER 9

SEWING MACHINES

Learning Objective: Upon completion of this chapter, you will be able to identify and maintain the different types of sewing machines used in the process of repairing or fabricating survival equipment.

Sewing machines are like any other tool you use. If you don't have the correct one, the task is harder or impossible to complete. The same applies to sewing machines. You need the right machine for the job; whether it be lightweight, medium weight, or heavyweight, there is a machine designed to perform each task. You work with various types of sewing machines in the process of repairing or fabricating items in the shop. You need to have all the knowledge and skill YOU can possibly acquire about these machines to fulfill your duty as a PR. If you don't know how to operate and maintain the sewing machines, they will stand idle, not operate properly, or not work at all. When you have a job to do, you need equipment that is operational. Without the proper knowledge of sewing machines, you will not have the confidence to perform necessary sewing machine repairs.

Before you can learn to operate and maintain a sewing machine, you must learn the language of the sewing trade. Through your supervisor and this text, you should become familiar with this language. It is very important that you form a habit of referring to the parts of a sewing machine by their proper names. It would be difficult to communicate with other PRs and impossible to pass a rating exam if you do not know the proper names of the different parts of a sewing machine. Take time to study the illustrations in this chapter that show the important sewing machine parts and their names.

Sewing machines are classified as two types- OSCILLATING and ROTARY. Both types are operated by electric motors and are fitted with rheostats and special clutch arrangements that enable the operator to control the speed.

When it comes to classifying sewing machines into oscillating and rotary, the important part is the rotary hook and oscillating shuttle. This is the device that is out of sight in the base of the machine, but does the very important job of forming each stitch after the needle has passed thread through the fabric.

Oscillating sewing machines have a sewing hook that rocks back and forth through half of one revolution to complete one stitch.

Rotary sewing machines have a hook that makes two complete revolutions to complete one stitch.

The type of stitch commonly used and made by sewing machines in repair work is the lockstitch. The lockstitch makes use of two separate threads. One comes from the spool down through the eye of the needle, the other from the bobbin. In making the lockstitch, these two threads must become interlocked, as shown in figure 9-1.

The thread passing through the eye of the needle is pushed down through the material being sewn. As the needle travels downward to the material, a spring pulls tension on the needle thread to keep it taut to prevent any slack that might tangle the thread around the needle.

After the needle reaches its lowest position and starts its upward movement, the process shown in figure 9-1 begins. A small loop of thread forms alongside the needle beneath the throat plate. The sewing hook catches this loop and carries it around the bobbin, which floats in its track in the bobbin case (view B of figure 9-1). By locking the loop of needle thread around the bobbin thread, the sewing hook forms the stitch.

As the needle completes its upward movement, the thread tension disks hold the needle thread firmly. The thread take-up lever, rising quickly, pulls on the loop that has been formed, and thus tightens the stitch. When the thread take-up lever

Figure 9-1.-The lockstitch.

reaches its highest position, the stitch is completed. (See views C and D of figure 9-1.)

Now look at figure 9-2. The standard sewing machine has four basic parts: bed, uprise, arm, and face. The BED (1) houses the linkage from the safety clutch pulley to the sewing hook assembly; the UPRISE (14) houses the arm shaft connection belt; the BALANCE WHEEL (12) is connected to the arm shaft in the ARM (11), which operates the needle bar mechanism in the FACE (6) of the machine.

Figure 9-2.-Sewing machine 31-15.

The machine is powered by an electric motor, which is connected to the motor driving pulley by a clutch. You connect the motor to the clutch by pressing the forward part of the foot treadle. The aft part of the treadle is the brake, which acts upon the clutch.

The material to be sewn is held in position on the feed dog by the presser foot. The pressure of the presser foot upon the material enables the feed dog to push the material forward each time the needle goes up. The pressure of the presser foot on the material is released either by a knee lifter or a hand lifter. The presser foot can be raised by pushing the knee lifter to the right. The hand lifter is located behind the face of the machine. The presser foot may be lifted and locked into position by raising the hand lifter to its highest position.