The sewing machine mechanism

I have always been fascinated by technology — even mundane, everyday household appliances have never ceased to pique my curiosity. As an engineering student I have had the opportunity to study the working of several simple machines. In my first year, I was fortunate enough to take the course ‘Reverse Engineering’ — a course which involved dismantling and putting back together machines like microwaves, printers and RC helicopters. In this process, we would unravel the mystery of how several appliances worked. I was able to understand their scientific principles and quench my curiosity regarding these puzzling appliances. One such appliance that has always left me baffled was the sewing machine.

My understanding of sewing was primitive, I understood it as a process where a needle weaves in and out of the upper and lower surfaces of a cloth using a single thread. This is why I failed to understand how the up and down motion of the needle in a sewing machine could achieve the same result. On further research, I discovered that the mechanism is shockingly simple and rather elegant!

A sewing machine uses not one, but two threads to create a seam — one from above and one from below. These two threads are intertwined with each other through the mechanism of the machine. The mechanism consists of three major components — a bobbin, a shuttle and of course, the needle. The bobbin is a reel of thread secured in the centre of the rotating shuttle — a hooked carrier with the function of looping the thread below through the one above. I have created a few illustrations (shown below, made using Adobe Illustrator) to aid the explanation of the system’s functioning.

Stage 1

The needle moves down and creates a hole in the cloth, through which it pushes the thread above the cloth (shown in yellow) down, allowing it to get caught in the hook of the shuttle rotating anticlockwise. At the same time, the thread loops over the thread below the cloth (shown in blue) which unravels from the bobbin.

Stage 2

The needle begins moving up, allowing the two threads to tighten.

Stage 3

As the shuttle completes a half rotation, the thread loses contact with the hook.

Stage 4

The needle moves up completely and the cloth moves forward, thus completing a stitch.

So there we have it — a simple, intelligent and extremely effective design!