How a Sewing Machine Works

Have you ever wondered what was inside your sewing machine? If you were to take the casing off, you would find an intricate set up of shafts, gears and mechanics that all work together to make your sewing machine run. Today, we’re going to take an up-close look at the part of the sewing machine where all the magic happens, the needle and bobbin assemblies, to see how stitches are formed.


View of the needle on the downstroke. Shown without thread or bobbin.

Creating a Lock Stitch

To understand how a stitch is made we’re going to take a look directly under the needle plate. Beneath the sewing machine’s needle is a bobbin, which is a small spool of thread. The bobbin sits in a shuttle that moves with the rhythm of the machine.

When you engage your sewing machine, the needle is pushed down through the fabric. Once the needle reaches its deepest level, it begins its ascent back through the fabric. As the needle begins to pull up, the friction of the needle against the fabric and thread forces the thread out one side of the needle creating a loop. The needle has a groove on one side, which allows the thread to slip without friction. Since the thread can slip on that side of the needle only one loop is created, on the opposite side of the groove. At this exact moment, a hook on the bobbin shuttle catches the loop of thread and interlocks it with the thread feeding off the bobbin. The two threads then interlock around the fabric pieces to create a lock stitch.

Some sewing machines, like the Sailrite® Ultrafeed LSZ-1 and LS-1, have a walking presser foot. This walking foot mechanism helps to ensure that proper stitches are created. The walking foot is timed with the machine to help pull the fabric into position for needle puncture on the downstroke and to hold it in place through the upstroke. By holding the fabric in place as the needle rises the walking foot helps to ensure that a proper loop is created under the fabric.


Thread loop being hooked by the bobbin shuttle. Shown without bobbin thread.

When Timing Goes Bad

This process requires exact timing within the machine’s movement to successfully create a stitch. When the timing in your sewing machine goes awry, it results in dropped stitches or other problems. If the hook reaches the loop too early or too late a stitch is not created. Similarly, as the needle rises, if the fabric is not secure against the machine it will rise with the needle and a loop won’t be formed.

If you experience dropped stitches with your sewing machine and you suspect timing issues, check your machine’s guidebook for more information. The Sailrite Ultrafeed Guidebook contains detailed troubleshooting solutions including how to reset your machine’s timing.

To learn more about Sailrite Sewing Machines, how they work, and all of their great features, visit

  1. Marilyn said:

    Great email!


    >________________________________ > From: Do-It-Yourself Advice Blog. >To: >Sent: Tuesday, April 15, 2014 5:27 AM >Subject: [New post] How a Sewing Machine Works > > > > >Nikki posted: “Have you ever wondered what was inside your sewing machine? If you were to take the casing off, you would find an intricate set up of shafts, gears and mechanics that all work together to make your sewing machine run. Today, we’re going to take an up-clos” >

  2. John said:

    Great explanation and photos. It’d be great if you could do a photo sequence, from the same point of view as that “hook grabbing the thread” pic, showing perhaps 20 steps in stitch formation as the thread is pulled around the bobbin. For those who don’t know what I’m talking about:

    For years I was puzzled about this: you have the main spool, and a piece of thread that leads off it into the sewn part of the cloth. You have the bobbin spool, and the second piece of thread that leads into the cloth. A “stitch” consists of linking these two unlinked pieces of string together, but how is that possible? The magic is in the bobbin: the hook grabs the loop that you’ve shown in the blog photo and actually loops it all the way around the bobbin case, which sits “floating” inside the hook assembly. It’s the same effect as if someone held the loop out from the needle and tossed the bobbin (trailing its thread) through the gap between loop and needle. The first time I realized this, I was in absolutely awe for days. Whoever really made that work — I think it was Singer — deserves the admiration of every engineer.

    Two consequences come from this: (i) there can be no sharp corners, burrs, etc., anywhere on the bobbin case or the part of the machine that the bobbin rests in, or the thread, passing over the whole assembly, will catch on them, at which point the game is over, and (ii) it’s really important to clear out any tiny bits of thread, dust, etc., that might accumulate in the bobbin area, even if they’re behind/under the bobbin, because they, too, will screw up the thread movement.

    I found that it’s easiest to see the stitch-formation process in a machine with a horizontal bobbin, where you can remove the cover-plate above the bobbin and watch every step. Sailrite’s machines seem to use vertical bobbins, but the ideas are exactly the same.

    • Nikki said:

      Thanks for your comment, John. Your observations are spot on!

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