The Six Stages of Sewing

Sewing Machine Time SeriesI have long been fascinated by sewing machines and how they work—especially because my theories on the subject have always struck me as absurd. I knew that a thread came from above, through the eye of the needle, and another from below, from a device called a “bobbin”—a word that sounds so British it seems like a crime, or at least indelicate, for an American to use. And that was about it.

Sewing Machine

Those interested can find pretty much everything they would want to know about how sewing machines work at How Stuff Works and Threads Magazine. What I’m interested in here is how that two-thread mechanism works. I figure that most people understand the rest of the machine, anyway. After all, it doesn’t amaze anyone that the pedals in the middle of a bike make the wheel at the back go around. So it shouldn’t be amazing that the needle and bobbin work in synchronization. But what’s up with that threading thing?

Two Thread System

When I was younger, I thought that through some amazing bit of technology, when the needle penetrated the fabric, the upper thread was removed from the eye and the bobbin thread was inserted into the eye. And then reversed on the next penetration. Wrong, of course. I knew that even as a child, but that was the best explanation I could come up with. In my defense, my 5-year-old’s theories about household plumbing turned out to be spot on.

What is really happening is much more clever than my dubious thought experiments. In all sewing machines that I am aware of, the upper thread stays above the fabric and the the bobbin thread stays below. The trick is that they wrap around each other under the fabric—whether the machine uses a bobbin or not. This is illustrated in the image below that I made from screen captures of a Wikipedia animated gif. [caveat]

Six Stages of Sewing

1. This is the set-up, just as the needle breaks through the fabric.

2. When the needle reaches full penetration, the bobbin hook grabs the upper thread loop.

3. The bobbin hook rotates in the opposite direction of the taut bobbin thread.

4. The bobbin hook continues to rotate the upper thread so that it wraps around the bobbin core—catching on the bobbin thread.

5. After the bobbin hook has rotated once around, it releases the upper thread.

6. The fabric moves backward, effectively moving the needle forward, and thus tightening the stitch.

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