Thread tension is one of the most critical elements of machine performance. In order to form a stitch correctly and ensure quality sewing, the amount of tension or drag placed on both the upper thread and the lower thread must be precise and balanced.

Think of the stitch process as a tug-of-war between the upper and lower threads. The desire is that neither overpowers the other. Too much tension on the upper thread (or too little on the bobbin thread) will result in bobbin thread being pulled up from below, so that it is visible along the edges of the area being stitched. Too little tension on the top (or too much on the bobbin thread) leads to loops forming in the area being stitched.

For the beginner, setting thread tensions can be a frustrating chore, as adjustments will have to be made periodically depending upon sewing conditions. For example, as a cone of thread gets close to the end, the tension tends to change. Thus, when you start to see the physical cone itself through the windings of the thread, it should serve as a reminder to pay close attention to the quality of the stitches being formed with that particular thread. In addition, different colors of thread have different tension requirements, as the dying process can affect the surface texture of the thread. This in turn can affect how easily it flows through the thread guides. Even humidity and temperature can affect thread tensions, as well as dirt and lint buildup along the thread paths.

Bottom-line, there is no “EASY BUTTON” as tension adjustment is an ongoing process. There are devices such as tension gauges available to help you set tension correctly, but ultimately you need to learn quick, simple methods to adjust thread tensions on the fly. Most experienced embroiderers can do it by “feel”, but it takes a lot of time to develop that skill. In the meantime, we will discuss a couple of simple tricks that you can use to adjust your tensions on a routine basis.

For the upper thread, most machine manufacturers offer some type of tool which will allow you to measure the tension. Using this data, you can make adjustments and then test the results. For example, Tajima has a device that looks somewhat like an oversized ink pen with a hook on the end.

Essentially, you “hook” the thread, pull on it with the gauge and take a reading. Make any needed adjustments, then take another reading. It’s a quick and simple process that works reasonably well.

With bobbins, you can also purchase a tension gauge which will provide you with a scientific way to measure the tension. As an alternative, you can also use the decades-old method known as the “drop-test”. It works for every make and model of machine.

Drop Test steps

1. Remove the bobbin case from the rotary hook.
2. Unwind the bobbin thread from the pigtail, but do not remove it from under the thread tension spring.
3. Place the bobbin case, with the bobbin installed, in the palm of one hand. With the other hand grasp the end of the bobbin thread, and gently pull out about 12 inches of thread.
4. Gently left up and suspend the bobbin case above the palm of your hand.
5. The bobbin should not drop, but remain suspended in the air about an inch above your hand.
6. Gently bob your wrist (hand holding the bobbin thread) and check that the bobbin drops a few inches then stops.
7. If the bobbin does not drop, then the tension is too tight. Adjust the tension screw (the larger one) on the tension spring (clip) counterclockwise to reduce the bobbin tension. If the bobbin drops freely, then the tension is too loose. Adjust the tension screw clockwise to increase it to increase the bobbin tension.

NOTE: IF dirt builds up under the Thread Tension Clip/Spring on the bobbin case, it will cause the tension to be too loose, no matter how much the screw is tightened. Each time you change out the bobbin, you should inspect and clean the bobbin case.

To be honest, more sewing tension problems are caused by the bobbin than the upper thread. However, since the upper thread is easier to access, more time is spent adjusting it, even though it may not be the culprit. So always pay close attention to the bobbin, even though it’s generally “out of sight, out of mind.”