How a bobbin works

edited to update:

I did not create this picture.  I thought it was clever.  I realize it’s not perfect.   Thanks for understanding.

No, I can’t change the graphic.  If you’d like to and email to to me, knock yourself out LOL

You can see the more recent updates at my new blog, here:


Wow, I got a bunch of new comments! Sorry, I just noticed them and approved them. Apparently it was on Craft Magazine, as well as Crafting Daisies and Dvorak’s site.  I am not sure where the graphic came from, it was sent to me a long time ago.

So, thanks for listening and for sharing!

Those of you wanting me to change or explode the design, I’m sorry, but I’m just a sewing mama that podcasts about parenting and sewing, I’m NOT a graphic designer or engineer. I thought it was interesting to share with my listeners. If you’d like to do a more complete graphic, feel free. I don’t go much past creating graphics using PhotoDraw.

I don’t have a ‘sweatshop’ machine or industrial one, just a Singer Ergo 3. 🙂


I had no idea how this worked until I found this little gem. I still wonder why they can’t make a machine that will take another spool of thread, thread it around so one can use that instead of having to wind bobbin after bobbin…..

No, I can’t change the graphic.  If you’d like to and email to to me, knock yourself out LOL



88 thoughts on “How a bobbin works

  1. I recently saw this question somewhere and the response was that if you had a large spool instead of a bobbin, the machinery (the red part in your picture here) would be really big and I think also that it would be too much wear on the top thread. Each little stitch length of top thread goes back and forth through the needle a whole bunch of times before it actually becomes a stitch you see on your fabric. So if the top thread loop was bigger (to get around a spool) then the thread would have to go back and forth through the needle even more.

    Does that make sense? I’m going to see if I can find a better explanation for this.

  2. kelley says:

    You can find more animated diagrams and explanations on the “” website.
    It’s very informative and great fun!

  3. SadPanda says:

    Either this picture makes no sense or I am too stupid: how can the green thread go completely around the white axis? That must mean the white axis is floating in mid air?
    Also, what is the red part connected to?

  4. anonymous says:

    >I still wonder why they can’t make a machine that will take another spool of thread,

    The bobbin has to “hop” through the loop so it can’t be too big.

    There are bobbin-less machines but they do a chain stitch instead of the interlock stitch. Surgers are often like this.

  5. Hector says:


    Sorry, but I’ve wasted too much money on Coats & Clark.

  6. what vicki says is right – if you watch the green thread, at the “bottom” of the loop, one part is in front of the lower bobbin and one half behind, so the top thread goes around the whole bobbin. if the bobbin was larger the loop of (green) thread would need to be bigger.

  7. damien says:

    the bobbin thread could be fed through the axel of the bobbin, end of size problem. i actually dropped sewing in school ’cause i could never get the bobbin right..

  8. Paul says:


    The bobbin is ‘floating’ in mid air, as the green thread goes completely around it.

    This still does not make sense to me…

  9. lonebear says:

    That is a good simplification. It becomes even more brain-sprain when you realize that the bobbon in the middle has a pin all the way through it. So the top thread doesn’t _actually_ go behind the bobbin.

    Then there is the entire foot plate connection. (The part that moves the fabric).

  10. Confused says:

    I still don’t understand how the blue spool is supported if the green thread passes both in front and behind it.

  11. bitterbean says:

    they do have machines that spool the bobbins for you, they are just industrial at not available at your local walmart or what have you.

  12. I just bought my girlfriend a sewing machine for Christmas and as she’s learned to wind the bobbin etc. I’ve been astounded the magic by which the machine works — now the mystery has been explained. Great!

  13. Anonymous says:

    actually, professional sewing machines do have a thing on top that winds bobbins…it starts spinning when you press on the foot pedal, so it winds as you go.

    quick & easy solution: buy a cheap motor and a 9-volt battery from radio shack

  14. Dirt McGurk says:

    Most sewing machines at least have bobbin rollers so you don’t have to wrap them by hand. I learned about this in a costume design class about two years ago and my mind was blown. This stitch is one thing, but some sewing machines can run a dozen or so different styles of stitches. All the same with just movement of the needle in relation to the bobbin and/or the timing difference between the two?

  15. So what’s holding the bobbin in place? The thread goes around both sides, so it’s not something in the plane of the picture, nor can it be something normal to that plane.

    Next time I’m visiting my Mom, I should just take apart the sewing machine. I’m sure she won’t mind….

  16. jay pugliese says:

    ok, her is how you make any size spool work instead of the bobbin.
    You mount the bottom thread spool outside of the machine and send the thread into the bobbin area from the back amd the mechanism does not have to be bigger, therefore no additional stress on the machine or thread.
    Jay, (Mechanical engineer)

  17. jimbunny says:

    There’s a tiny error. The needle pulls up before the red thing grabs the thread. When the needle lifts, a loop of thread stays behind from friction with the material. The red thing can then go through that loop and form the stitch.

  18. SKL says:

    Graphic is nice. However, it may not be accurate. The green thread revolves 360 degrees around the middle circle.

    What holds the middle circle there? How can you attach it without stopping the green thrad from revolving?

  19. Actually, my mother’s sewing machine does, in fact, have a bobbin winder on it.

    I’m not sure if that’s what you’re lamenting, but it takes a bobbin and a spool of thread and spins them to wind thread onto the bobbin, using the same motor that runs the machine normally.

    Takes about 15 seconds.

  20. m says:

    Professional sewing machines have a device on top of the machine that winds a bobbin from a separate spool of thread as you work.

    You wind bobbins by hand? You can just get a cheapo toy motor and a 9V battery from Radio Shack if you don’t own a sweatshop machine…

  21. Actually they DID make a machine that did just that (use a spool of thread instead of a bobbin for the bottom)!!
    Eldredge made a treadle machine called the Eldredge Two Spool, a very sought-after machine by us quilters who use treadle machines.
    I don’t know why the idea didn’t catch on…..

  22. Char Lyn says:


    Your statement is very correct, but it would still be possible to have a spool instead of a bobbin by using slightly different mechanics. Sergers use spools for bobbin thread, and if you only use two spools instead of four, you can do a simple straight stich–for miles.

    Nutmeg–thanks for the post!

  23. Nick Radonicsew says:

    Sorry this is not quite complete enough.

    This is a 2 d projection showing string go above and below the bobbin. The bobbin still needs to be supported in 3-space, so it can’t just float in position. Something is missing. I’d like some orthogonal views as well. Maybe exploded views as well.

  24. Neat little diagram. It is quite mesmerizing, lol. Thanks for the enlightenment and for the how things work website suggestion. Oooh, goodie, another site to surf!

    Hector mentioned the need to use good thread. What qualifies as good thread?

  25. Steve R says:

    The top (needle/green) thread is punched through the fabric under tension (from the tension discs). The rotating Hook (red) picks up the top thread as the needle withdraws, then pulls the thread in a loop OVER the top of the bobbin i.e. both parts of the thread loop pass over the face of the bobbin. The tension discs release to prevent the threads from breaking due to friction.
    After the half-way point of the loops’ travel over the bobbin, the tension discs on the upper thread close again and the top threads’ take-up arm pulls the loop tight, carrying the bobbin thread (blue) up to the underside of the fabric and locking it against the fabric. How far it pulls the bobbin loop up is a function of how much top thread tension you ‘dial in’ to your machine. More for thicker fabrics, less for thinner and for embroidery/buttonholes. This is why bobbins must be threaded into the machine before you start to sew: the threads must be in the correct sequence for the system to work.

    You can see all this in operation by leaving the bobbin cover off your machine and winding a stitch through by hand. Internally, the sequence is all worked out by cams (this includes the action of the feed dogs and presser foot, too).

    Two different designs of bobbin can be used in domestic machines: front mounted or top mounted. Front mounted bobbins (see the graphic above)need a case to support the bobbin which includes a bobbin thread tensioning mechanism; top mounted bobbins generally drop into place under a transparent cover in the needle plate and must be threaded through an integral tension mechanism.
    Front mount advantage- the top thread loop rotates in the same plane as the needle, so there is far less friction on the thread as it’s pulled through the needle. Disadvantage- you cannot easily check when you’re running low on bobbin thread.
    Top mount advantage- the transparent cover lets you easily check your bobbin thread capacity. Disadvantage- the top thread must be rotated by the hook at right-angles to the needle, putting a lot of drag on the top thread as it passes through the needle.

    BTW: Better quality machines and most industrials have front mounted bobbins. (Something to look for when you buy a machine!)

  26. Steve R says:

    After re-reading my post, I feel that I didn’t explain myself very well.

    With regard to the top threads’ path around the bobbin, the hook (red) picks up the loop of the top thread (green) then turns the thread around bobbin case; one half of the loop slides across the face of the bobbin case, the other half is dragged around the outside of the hook in a shallow groove. This has the effect of twisting the upper thread around the bobbin thread (a half-twist, actually). The top thread slides off the hook as it completes its circuit and is then tightened around the bobbin thread and pulled into place by the take-up arm (the ‘feed’ thread from the supply spool is held ststionary by the tension discs to make the take-up arm pull the needle thread up)
    Sorry for the confusion! 🙂

  27. Aurelia says:

    In response to SadPanda – the thread goes over the top of the bottom on a horizontal bobbin machine or along the side of the bobbin away from the post on a machine with a vertically positioned bobbin. The view above would be like looking from the side with the post. Run a machine a few stitches without the bobbin cover in place and you’ll see it.

  28. pam says:

    great graphic. Thank you. I have just been given an old ‘Magic’ Singer sewing machine and cannot thread up the bobbin. Can’t find a manual or anything about this machine online to assist. Anyone heard of this machine?

  29. Jose Pappen says:

    Dear Nutmeg,

    Can you kindly edit the demo.

    Nice demo, very simple although a little slower would have helped more. However what SadPanda first pointed out first and then by Nick Radonicsew is valid. There is a small mistake which Steve R has tried to explain. If at all it is not clear, I would like to put it in simple words.

    As the red hook of the bobbin cover drags the green thread around the blue thread, both the sides of the green thread passes in front of the round in the middle.

    In other words, the green thread never passes behind the round face of the bobbin in the middle, it is always in the front.

    Otherwise it would be practically impossible unless you hire some magician to have the bobbin floating (pun intended).

    Anyway nice work.

  30. Sinead says:


    Do all sewing machines need a bobbin as I have a singer kids one and I cannot find where the bobbin goes and the instructions do not say…:(


  31. Sebastian says:

    I’m not at all sure that the green thread would still wrap around the blue thread if both halves of the green thread slide along the FRONT of the bobbin- However, SadPanda is completely correct in observing that the animation doesn’t hold up as it stands. I STILL DON’T KNOW HOW THIS THING WORKS!

  32. Sebastian says:

    After thinking for a while: Maybe the whole Bobbin mechanism IS free floating inside of a housing (which is not shown in the animation). This would enable one half of the thread to pass behind the Bobbin. The housing could rotate the Bobbin either through a magnetic field (the Bobbin being like an anchor in an electric motor), or through rubber friction wheels in the walls of the housing, and running over the threads when they pass by.

  33. claire says:

    wow what a wonderful example the bobin demonstration really helps me be aware of what is happening with my machine thankyou

  34. Pamela says:

    Wow, I thought it was good.
    Can anybody help me. I havent used a sewing machine is almost 20 years and I cannot figure out if Im doing the bobbin correctly. I tried to find a video for a side loading bobbin then when I think I may have it loaded correctly it will not feed correctly with the top thread it just knots up and I am wasting so much thread. I then remembered I have to hand start it and have about two inches of the thread together then start sewing. Well I dont know if the bobbin is load correctly, where do I put the thread from the bobbin? How to get bobbin thread and top thread to stitch together? Anyone know any website with videos for his since I know no one that can physically help me? My email is

  35. _zK; says:

    you guys are soooooooo STUPID.
    no, nothing floats in mid-air.
    the red part, is connected to the machine itself,
    so that you can load and unload the bobbin, and so that you can make these stiches.
    and the inner white circle is the bobbin.
    seriously, its common sense.

  36. Emelie says:

    In my machine, the red thing doesn’t complete the rotation. The hook fetches the thread, revolves about 180 degrees, then stops, releases the thread and reverses back to the starting position again.
    Sebastian (#65), you’re right. The bobbin and its housing fit snugly in a hollow space, but the only part that’s actually attached to the rest of the machine is a sort of crescent shaped part that conveys the motion of the motor to the bobbin housing. Together, the crescent shape and the outermost part of the housing form a circle that has two slits in its perimeter, allowing the green thread to pass.
    Hard to explain, but it really is an interesting, beautiful machine!

  37. A machine that sews with a spool of thread for the bottom thread is called a “Chain Stitch” machine (a serger is one type of chain stitch machine) vs. the “Lock Stitch” that you have. With most chain stitch machines if you break one thread it can unravel the stitches quite easily.

    The reason the bobbin is so small is that the top thread actualy goes all the way around behind the bobbin (between the hook basket and the hook base) to complete the stitch.

    It’s easier to understand if you turn your machine over slowly by hand while watching the process.

  38. Pingback: How a Bobbin Works
  39. I went to a demonstration on how to make shade sails. There was a commercial machine there that blew me away. It had a double needle setup (commercial size cones) and two more cones that threaded to the bottom of the machine – no bobbins! Somehow someone figured out how to do it. No, it was not a serger. I got the name of the company, but haven’t inquired further yet. Here is their website:

  40. A great illustration – but this has been on the internet for at least 15 years! Originally was on one of the very early collector (sewing machines!) site. It’s a bit harder to understand if you are using a horizontally mounted rotary hook machine – as most do today. The picture illustrated what happend in a front, vertically mounted hook. Google “How Sewing Machines Work” and it will lead you to a new world of discovery… once you know how they work, you can know how to work them!

  41. There is a magnet in the base of the bobbin cup which secures the bobbin holder, but allows the thread to pass under the bobbin. That eliminates the need for a shaft. The thread DOES indeed go all the way around the bobbin. That may clear up the mystery about how the threads twist together to form a full stitch.

    The thread is doing lots of traveling each stitch as it pierces the fabric, is snagged by the hook, then pulled entirely around the bobbin and its carriage, then pulled back up (see the top hook in its travels up and down each stroke) to pull the tension onto the thread for a balanced stitch. Slow it’s fascinating, but running fast, it is just incredible that it gets it done without missing.

    That one thing of the loop making it completely around the bobbin holder each stitch at speed, should be proof enough that the machine needs to be kept free of lint at all times. Also, the size of the needle groove needs to be matched with the size of the thread; course thread, larger needle, small thread, smaller needle. Those two things will save you a lot of dropped stitches. Hope this helps.

  42. In the graphic, the bobbin floads freely in an assembly, the red thing the grabs the green thread. The green thread is pulled completely around the bobbin. That’s kind of hard to display in a 2-D graphic.

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