The Differences Between Sewing Machine Rotary Hook and Oscillating Hook Systems
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 both the rotary hook and the oscillating hook.
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Rotary Hook vs Oscillating Hook Sewing Machine Systems
I would like to start by explaining the differences between the rotary hook and the oscillating hook. As well as, 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.
What does the sewing machine hook do?
The term hook refers to the ring with a pointed finger that 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 its downward 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 counterclockwise. 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. This video shows it in large format to make it easier to understand.
Rotary Sewing Machine Hook System
If we are using a rotary hook system then our hook continues to travel in one direction. It carries the top thread all the way around the bobbin case wrapping the thread loop over around the bobbin thread. Then release the loop on the opposite side of the bobbin forming a stitch. As the needle comes down the take-up lever on the head of the machine is positioning itself to lift the top thread up and tighten the stitch by pulling the slack from the loop up against the take-up spring and ultimately the tension disks themselves.
Oscillating Sewing Machine Hook System
If we are using an oscillating hook system then the physics of the stitch formation stays the same. How the top thread is carried and released differs. An oscillating hook picks up the top thread exactly like a rotary hook. 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 take-up lever serves the same function of removing the slack from the loop and tightening the stitch as it did with a rotary system.
The actual hook motion of an oscillating system stops as the loop is 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 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.
Rotary Hook and Oscillating Hook Systems in Action
We have had several people reach out wanting to see the hooks actually moving to get a better visual. Mel put together a short video showing both hooks moving.
Myths and Truths About Rotary Hook and Oscillating Hook Sewing Machine Systems
Now let’s discuss some of the advantages of both sewing machine hook systems. I will also be laying to rest some of the most common misconceptions about a very simple process.
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Myth – Oscillating Hook Systems Make Weaker Seams
The first misconception I would like to put to rest is baffling me as to how it ever became folklore. Folklore facts are facts based on legendary myths. No one remembers how they got started generations ago, no information to back up the myth but the myths are now factual because they have been repeated for so long that 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.
Truth – Rotary Hook Systems Are Faster
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. 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 hook never changes direction. The vibration, speed, and noise caused by the vibration are all directly related to the start-stop motion of the hook.
Myth – Rotary Hook Systems Are Better
Now you may be thinking that the rotary hook 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. That 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. They don’t have to use an internal belt or chain to keep the hook timing in sync with the needle timing. There are fewer rotating parts to wear so they tend to require less maintenance. Also, they are more forgiving when it comes to timing issues. So now it might look like the Oscillating hook may be a better design.
Myth – All Rotary Hook Machines Are Class 66 and Horizontally Orientated
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 orientated. 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. Several manufacturers 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 have nothing to do with hook systems. Side loading, top loading, and front loading don’t determine the hook system.
Rotary Hook Machines Can Be Picky
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 to 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 a very heavy thread to a very fine thread. It baffles me because the physics and dynamics are identical when comparing the systems.
Conclusion – Which Is Better Rotary Hook or Oscillating Hook Sewing Machine System
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 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. If you have to take it to a shop or tear it down after 10 years of use, you will probably need to do it Oscillating machine before the end of the 11th year.
Also 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’s advantage would make an ounce of difference to the end results of the project.
Don’t forget to check out our other sewing machine posts, learn more about repairing vintage sewing machines, and our quilt patterns.
Until next time as always enjoy your machines your way and may your needle strikes be few and far between.
