Study on lock stitch machine / feature of lock stitch / machine function / machine maintain system/ advantage & disadvantage

Lock stitch is one of the important stitch types among all the stitches. It is used to make pant, shirt, dresses and various parts of the apparels. Plain sewing machine machine

is used for lock stitch. Plain sewing machine is also called lock stitch machine to operate this machine one should have practical knowledge about plain sewing machine.

Sewing machine

Lockstitch:

• A lock stitch is the most common mechanism stitch made by a sewing machine
• The lock stitch uses two threads, an upper and lower. Lock stitch is so named because the two thread, upper and lower”, lock” (entwine) together in the hole in the fabric which they pass through.

Lock stitch

Feature of lock stitch:

1. Lock stitch has a widest application in garment sewing
2. Lock stitch is formed by two different thread system
3. In the sewing techniques, a needle thread is interlaced with the bobbin thread
4. Face and back has some appearance
5. The stitch is different to unpick

Parts of lock stitch machine

Principle of lock stitch formation:

Lock stitch formation is very important for stitching mechanism. The mechanism of lock stitch formation can be illustrated as below-

The five steps of a lock stitch formation: 

Step -1

Needle penetrates the fabric to bring top thread into bobbin area

Step -2

The needle begins to lift and as the needle rises, top thread forms a loop for shuttle hook to catch. 

Step 3

Shuttle hook carries the thread loop around and under the bobbin case.

 Step 4

Loop slides off hook and bobbin case, goes around bobbin thread. 

Step 5

The threads are pulled up and are set into the fabric as a lock stitch.

Different  Parts of a Sewing Machine and Their Functions:

Bobbin: Bobbin holds the thread inside the machine. Bobbin is a small yarn package. It is used for storing specific amount of sewing thread on it (Lower thread). Bobbin is a spool underneath the bed that provides the lower thread.

bobbin

Bobbin case: To hold the bobbin in the particular place of the machine. To control lower thread tension.

Bobbin case

Thread Tensioner: To maintain the uniform tension of sewing thread (Top thread) during sewing.To control the tension (i.e. increase & reduce the tension) of the swing thread during sewing.

Tensioner

Thread guide: It holds the thread in position from the spool to the needle.

Thread guide

Stitch density controller: It is used for increasing and decreasing the stitch density per inch during sewing.

Hand wheel:A wheel located on the right side of the machine which is driven by the motor; although it can be turned manually.

hand wheel

Needle:To make a hole on the fabric surface for passing the yarn from one side to another.

For completing sewing action.

needle

Machine maintain system

Oiling:

• Points of lubrication: Every surface on a machine, which is in movable contact with any other point, must be lubricated. This is true even if the operators manual does not indicate the need to lubricate every point. A small drop of oil on each point is sufficient.
• Frequency: Each lubrication point should be oiled every four hours of use.  The hook race, and corresponding bobbin case or bobbin case base, and the needle bar, all require particular attention to lubrication. These are some of the primary wear areas on lock stitch sewing machines, (the needle bar on lock stitch machines)
• Oiling systems: Manual oiling systems require the operator to oil each point individually, and on a regular (preferred 4-hour) basis. Automatic oiling systems can supply all points of lubrication or can be combined with manual oiling. 
• Cleaning
• Hook system
• Thread handling system
• Needle bar
• Adjustments

Advantage

• No seam impression on thin woven fabric
• Lower thread consumption than double chain stitch

• Same seam strength on the upper and lower sides
• Good seam strength owing to interlocking in the middle of the materials ( but not as strong as with the chain stitch)
• Easy tying of the seam end by reverse sewing

Disadvantage:

• Considerable mechanical stress on the sewing thread when forming the stitch
• Lower productivity owing to bobbin changing

Bartack:

• Double lock stitch for separate tying of the start and the end of seam 
• Double lock stitch for tying belt loops, for example 
• Double lock stitch bar tacks for strengthening jeans pockets for example