The Differences Between Rotary and Oscillating Sewing Machine Hook System

Hello everyone today we are going to be talking about the hook systems most commonly used in conjunction with round bobbin lock stitch residential sewing machines. Regardless of the vintage or the manufacturer of your sewing machine, if they use a round bobbin then they will use a rotary or oscillating type of hook system. We will be discussing the differences, the performance, and the versatility of the two systems.

difference between rotary and oscillating hooks

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I would like start by explaining the differences between the two systems and the resulting mechanical requirements needed for each system to function appropriately. To do this we must first understand the definition and the purpose of the hook. The term (hook) refers to the ring with a pointed finger which surrounds the bobbin case.  The needle carries the top thread down through the material while the hook is revolving around the bobbin. When the needle reaches the bottom of it down ward travel and starts upwards a small loop is formed in the top thread right behind the needle. This loop is carried up with the needle. The hook revolutions are timed so the point of the finger goes through the loop, catching the thread and pulling it down as the needle continues up. This process is identical regardless if it is a rotary system or an oscillating system. But within the next quarter of a revolution, the difference between the two becomes obvious. Our needle is still traveling upwards as our hook passes the 3:00 position on a clockwise revolving hook and 9:00 if the revolutions are counter clockwise. The easiest way to identify clockwise or counterclockwise is to look at the point of the hook. The point basically leads the hook. If it points right it turns right or CW, if it points left then it is CCW.

If we are using a Rotary system than our hook continues to travel in one direction carrying the top thread all the way around the bobbin case wrapping the thread loop over around the bobbin thread and releasing the loop on the opposite side of the bobbin forming a stitch. As the needle comes down it pulls the top thread up and tightens the stitch.

rotary hook bobbin assembly

If we are using an Oscillating system then the physics of the stitch formation stays the same but the manner in which the top thread is carried and released differs. An Oscillating hook picks up the top thread exactly as a Rotary. But instead of carrying the loop completely around the bobbin it only carries it far enough past center for the pressure of the needle pulling the thread up to pull the loop off of the point of the hook. The loop still travels across the face of the bobbin and wraps the bobbin thread the same way it does with a Rotary system. The actual hook motion of an Oscillating system stops as the loop is being released from the point and reverses direction or travel. The needle does not stop or change direction it continues on to perform its duties. When the needle has reached the top and starts back down the hook is still in reverse, It stays in reverse until the needle has tightened the stitch and has reached the bottom of its down stroke. At this moment in time, the hook has reversed far enough for the point to be on the opposite side of the needle than it was when the loop was released. As the needle starts back up and the loop starts to form, the hook changes direction again so the point is leading it as the needle pulls the loop up. When the needle pulls the loop in front of the leading point the hook picks it up and starts carrying it down again to make another stitch. This reversal of directions is the basis for the term and the name Oscillating hook.

oscillating hook assembly

Now that we have covered the basic differences between the two systems we will discuss some of the advantages and disadvantages of both systems. During this discussion, I will also be laying to rest some of the most common misconceptions that falsely misrepresent facts and confusion to a very simple process.

The first misconception I would like to put to rest is baffling to me as to how it ever became a folklore fact to begin with. Folklore facts are facts based upon legendary myths. No one remembers how they got started generations ago, No information to back up myth but the myths are now factual because they have been repeated for so long they must be true. Rotary hook machines make exactly the same lock-stitch stitches as an Oscillating hook. It is impossible to look at the two rows of stitches and tell the difference between the seams. They are Identical. So to fall into the concept that either system makes a stronger stitch is ludicrous.

Now for a touch of truth, Rotary hook machines operate with less vibration than an Oscillating hook machine. They also tend to be slightly quieter than an Oscillating hook and they are typically the chosen system for high-speed machines. All three of these facts are true due to the forces at play as the Oscillating hook must stop and reverse directions twice during a stitch and a Rotary never changes direction. The vibration, speed, and noise caused by the vibration are all directly related to the start stop motion of the hook. Now you may be thinking that the Rotary system is better. So we will shed some light on a few different facts. Oscillating hook machines are simpler to manufacture, they require fewer parts which means they can be produced at a higher rate resulting in more machines per hour thus helping to cut cost per machine.  The hook action is driven by offset cams and linkage between shafts, therefore, they don’t have to use an internal belt or chain to keep the hook timing in sync with the needle timing.     There are less rotating parts to wear so they tend to require less maintenance and are more forgiving when it comes to timing issues.  So now it might look like the Oscillating hook may be a better design.

While we give ourselves a break to digest the information each in our own way I would like to shut down a couple more misleading concepts, such as all rotary hooks use class 66 bobbins and they are all horizontally oriented. Both are false. Bobbin orientation has no bearing on the hook system used in a machine. Nor does it matter which style bobbin the machine uses. Class 66 and class 15 bobbins may be the most commonly recognized bobbins universally, but they are not the only ones supporting the lock stitch machines and a lock stitch machine has to have a round bobbin. Just to name a few machines that do not use either class 66 or 15 bobbins. White used 2 different sizes of bobbins in their lockstitch machines and they originally used a very unique bobbin case, not all Necchi machines use class 15 bobbins. There are several manufacturers who have used Apollo bobbins (very close tolerances to a 66 but not fully interchangeable). Elna and Bernina also have their own bobbin and hook designs while still supporting the standard lockstitch. I’m sure I have probably left some out but I hope to have gotten the idea across. Orientation and bobbin class has nothing to do with hook systems. Side loading, top loading, and front loading don't determine the hook system.

The last thing I would like to share is partially my own experience and research. I am a little apprehensive about stating this as a positive fact but I have done the follow-up research on the experience so I do feel like it is worthy of being mentioned.

What I have experienced and then researched to verify is hard for me to fully understand. So here it is for what it's worth. Rotary systems seem to be finicky when it comes to thread size. If the machine is set up for a heavier thread it will perform just fine but if the thread size is changed then it may start skipping stitches. If the timing is re-adjusted and needle height reset for the finer thread it will again be a perfect stitcher. As soon as I tried to go back to a heavier thread it started dropping stitches again. And again the solution was reset the timing and needle height. I played with this on several different machines and although some were more forgiving than others they all seemed to be prone to acting in this manner. When I tried the same test in several of our different Oscillating hook machines I discovered that they are not nearly as finicky about changing thread sizes or types. The only times I would see consistent problems was when switching from very heavy thread to very fine thread. It baffles me because the physics and dynamics are identical when comparing the systems.

So what does all this really mean? Which hook system is the best? Well, I don’t believe there is a single solution. So I am going to give you my opinion and let you decide what works best for you.

If you need a fast machine say above 1200 stitches per minute or you want a quieter smoother (fewer vibrations)  machine and it doesn’t need to constantly change thread size and types then my vote would be the Rotary, keeping in mind they require more maintenance as a group than the Oscillating counterpart. By more maintenance, I do not intend to imply they are problematic. They are not. If given exact circumstances side by side the Rotary will need attention and tuned up before the Oscillating hook so if you have to take it to a shop or tear it down after 10 years of use you will probably need to do the Oscillating machine before the end of the 11th year.  If you don’t normally sew at speeds above 1200 stitches per minute and you sew a constant regimen of changing media then the answer would be an Oscillating hook system. With all this being said one should always remember that anything mechanical will break, they all require routine maintenance and cleaning. Neither one of these systems is flawless and with a little TLC either one of them will give years of service and enjoyment for the average home sewing enthusiast. Here in the Quilt Room, we use both systems and never give much thought to what system we are using at the time. We rarely have an occasion when one system advantages would make an ounce of difference to the end results of the project.

Until next time as always enjoy your machines your way and may your needle strikes be few and far between.

difference between rotary and oscillating hooks

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About Melissa Shields

Mel is a 30 something year old quilter, attempting to balance her old school roots with today's trends. When not sewing or shopping for a new sewing machine Mel enjoys reading, reality TV, and Nascar.


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