How a Bobbin Works

Posted in: How Things Work — By on November 4, 2010 7:14 AM

We found this really cool diagram/animation on the Material Mama blog and thought Sewing School students would benefit from it’s awesomeness.

This animation demonstrates how a sewing machine works – specifically the bobbin mechanism. You know it’s doing something down there to keep things together while you sew, right? Well this is what it does!

You can see how the blue bobbin thread is wound around the green top stitch thread as you happily stitch away.

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  1. Bruce Gordon says:

    It still looks like the bobbin is floating in air and the thread is passing on both sides of the bobbin. It is a neat graphic but does not answer the question of how the lower thread gets through the loop!

    • James Barry says:

      The hook on the bobbin casing catches ahold of the thread brought down by the needle and rotates it UNDER the thread fed by the bobbin spool. In doing this, it in effect winds the needle’s thread around the bobbin’s thread. In drawing the needle back upward, the tension upon the upper thread pulls the bobbin thread up and over the spool’s exposed center (which is not connected to anything on this side), and a stitch is formed! I hope this helps; I just discovered this myself!

      • Mohamed Zeyada says:

        You are right, the bobbin should be floating so that the upper thread can go over and around the bobbin’s spool, then it can take the lower thread when the needle goes up, thus a stitch is made.

    • dee says:

      In fact what is actally happening is this: the bobbin thread is being passed straight through the loop that is made with the top thread. Nothing is really ‘wound’ around although it looks like it is. The hook on the bobbin case is narrow where it picks up the needle thread, and is wider further around the case. This causes one thread of the loop to slide under the bobbin, while the other slides over the top of the bobbin– effectively passing the bobbin thread through the loop omade with the top thread. As the needle lifts, it pulls the top thread up, thus bringing the bobbin thread with it to create the stitch. If the tension on either thread is too tight, that thread will lie flat against the fabric and will pull the other thread to the same side — thus making a stitch that is uneven and both threads will show on that side. This is used for basting, where you increase the stitch length, and tighten one thread so it can be pulled and the stitching will come out.

    • Stephen Lennon says:

      I sympathise with your confusion. I have wrestled with this puzzle myself. In order to answer it I researched it extensively and actually disassembled a sewing machine to solve the question. Many of the answers you will find to the question online are beside the fact and overcomplicated. So are you ready for the answer?

      It happens exactly like the image above!! The top thread actually passes around the entire bobbin. This is the reason that a bobbin is required at all, if the top thread did not pass around it then you could just use a second spool. The bobbin is required because it is small enough to allow the top thread to pass around it without requiring a massive take-up lever to let out and retract the top thread each time. The take up lever is a reasonable size because the bobbin is small and the top thread can pass around it with abut 5 cm spare thread, which is then retracted by the take-up lever as the stitch tightens.

      And now for the last piece of the puzzle: “If the bobbin is on a shaft, how does the thread pass through the shaft?” Well, the top thread passes behind the shaft because the shaft is part of the inner bobbin case, and the top thread passes BEHIND (Or beneath) the inner bobbin case, and therefore behind or beneath the shaft therein, if there is one at all.

      To flesh out the mental image, conceptualise this configuration that describes the drop-in (Horizontal) bobbin of my Singer Confidence:

      You have a bobbin;
      It fits into an inner bobbin case;
      The inner bobbin case rests in BUT IS NOT ATTACHED TO an outer case;
      The outer case incorporates the rotating hook and is attached to the frame of your sewing machine.

      The inner bobbin case fits into the outer case. In my machine the inner bobbin case has no shaft going through the bobbin, but it wouldn’t matter if it had. The inner bobbin case is not attached to the outer case though they do touch, it merely rests inside it and is prevented from rotating by its shape and various protrusions on its edges.

      The outer case incorporates the pickup hook which catches the top thread when the needle has plunged down, it then drags the top thread around the bobbin thread and therefore completely around the entire bobbin, passing the top thread through the free channel between the inner bobbin case and the outer case.

      In short: There is no magic … just good science :) If you still don’t understand then you will have to find a machine and take off the plate under the presser foot and observe for yourself as you manually turn a stitch.

  2. lenso7 says:

    in reality the bobbin never experiences full rotation. but in this animation, it does. So it doesn’t explains the puzzle piece. Answering this Question will give you the answer. What happens when the bobbin picks up the thread in half rotation provided the bobbins moves in both Anti clockwise at first and then clockwise at second?

  3. RANJITH says:

    My sewing machine doesn’t stich continiously. It stich 5 times correctly then 4 stiches not. Please reply me

  4. Diane Augustin says:

    I showed this to my sewing students today and they lived it.

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