Main parts involved
Before looking at how this equipment works, here are the main parts that are involved in this process:
- Thread tensioning discs
- Feed dog
- Presser foot
- Shuttle hook
- Electric motor
How a basic sewing machine works
What you see is the needle starting off at a high position, then moves down the fabric and back up again as you run the machine or as you step on the foot pedal.
What you do not see is the needle feeding the thread that passes through its eye to the hidden mechanism below so as to form a stitch.
With the needle driving down through the fabric so as to reach the low position, it creates the hole through which the thread will pass through, then feeds its thread to a rotating shuttle hook in the bobbin compartment while at the lowest position just before going up.
This shuttle hook spins and loops the needle thread around the bobbin spool thread, causing them to interlock and thus, creates a lock stitch over the fabric that ties it together.
As the needle begins to go up, it tightens the thread and consequently, tightens the stitch by pulling up the thread that it supplied down there. Thread tensioning discs along the threaded upper part of the machine also help in keeping the needle thread tight so that the stitches created are firm.
Everything is interconnected in these machines and as soon as the needle rises above the fabric, a set of feed dogs pull it in at an even speed so that all the stitches formed later on have the same length.
To give these feed dogs the required grip, a presser foot above presses the fabric tightly over them, enabling their teeth to grab onto the material and move it almost effortlessly.
Repeat the above steps
Once complete, this cycle occurs, again and again, creating a continuous lock stitch, and can only be stopped by letting go of the foot pedal, an empty spool or an empty bobbin.
Modern sewing machines feature several types of stitch patterns and using the zigzag stitch as an example, instead of the needle piercing through in a straight line, it shifts position after every cycle to the left then right, depending on the width set, and this forms the different pattern.