Getting the perfect stitch is the goal of all sewing – It is fine to use different threads in the top and the bottom, whether they be different fiber types (for example, cotton and polyester) or different thicknesses. Adjustments for these differences are made with the tension settings, usually to the top tension, but occasionally to the bobbin. Machines differ in tension settings from brand to brand. Some machines seem very eager to please and they love everything we do. Other machines require lots of attention and extra training. Most machines are somewhere in the middle. Even within brands, there is some variance from machine to machine. Just like a dog, if we learn how to train or adjust the machine, it will serve us well and bring much happiness. An untrained machine (and dog) can cause more frustration than joy!
If adjusting your top tension doesn’t work, you may need to loosen your bobbin tension – If you have experienced problems running decorative threads and have adjusted the top tension every possible way and still cannot get good results, the solution might lie in the bobbin tension setting. For example, if the top thread is breaking because the top tension is too tight, it is necessary to loosen it. If you loosen it to the point where the thread does not break, but the top thread then loops on the back, the top tension is now too loose.
This is a common problem with some longarm machines. – Neither of these solutions work and adjusting the tension settings in between these two extremes doesn’t work so what can we do? The problem is that the top tension and bottom tension are too far out of sync so no matter what we do to the top tension, it will not solve the problem. In order to fix this, we must loosen the bobbin tension. Many of us were taught to NEVER touch the bobbin tension. That was when thread choices were very limited and decorative threads hadn’t yet been invented or used on high speed and longarm machines. Times have changed.
How to change your bobbin tension – If you can thread a sewing machine, you can adjust the bobbin tension. There is no need to spend money on a second bobbin case. With a permanent marker, put a dot where the tension screw is now pointing to so you can always return to the original setting. Then, with a screwdriver and thinking of a clock, make adjustments by turning the screw equivalent to what a 10-15 minute movement would be. Counterclockwise loosens the tension (the most commonly required adjustment) and clockwise tightens the tension. Remember, “lefty loosey, righty tighty”. For longarm machines, the bobbin tension should be loose enough that if you hold the bobbin case in your left hand and pull the thread up with your right hand, the bobbin case should not lift off your left hand. The old “4 inch drop test” is gone. Now, after having loosened the bobbin tension, any adjustments you make to the top tension will be more effective because the top and bottom tensions are more in sync. You should be able to pull the thread through the needle fairly easily without feeling much tension. You have now been given permission to adjust the bobbin tension! It will make a huge difference.
Preset – Sewing machines are factory preset to have the top and bottom thread form even stitches. If the top and bottom threads are identical in fiber and weight, adjustments should not be necessary. However, if we use cotton on top and poly underneath, or metallic on top and poly underneath, or a heavy thread on top and a thin thread underneath, it is necessary to adjust the tension settings. It is fine to use different thread types and weights on the top and bottom.
Tug of War – Think of the top and bottom thread as having a tug of war. If the threads are identical and you are sewing on a single layer of fabric, both sides have equal strength and the result will be a draw. The sewing should therefore produce perfectly even stitches with no top thread showing underneath and no bobbin thread showing on top. However, in the real world, the teams are rarely equal. We use decorative threads on top. We often use different fibers for the top and bottom threads. We also add stabilizer or batting. Sometimes we might use a cotton bobbin thread and other times we use a polyester bobbin thread. All these factors make it necessary to adjust the tension for each project. By adjusting the top tension either up or down, we are able to add or take away strength on the top thread team to equalize the tug of war battle.
Considerations – Here is a list of things that affect stitch results: Batting – This adds drag on top thread. Cotton batting tends to grab the thread more than poly batting, adding more friction on the thread. Fabric type – Dense fabric puts more stress on the thread. Top thread thickness and type – Metallic is less flexible than cotton or poly. Poly is stronger than either cotton or rayon. Bobbin thread type – Cotton bobbin thread tends to grab more than a silk-like filament poly. Sometimes grabbing is preferred and sometimes it causes problems. A silk-like filament poly thread (not spun poly) in the bobbin will work better with metallic or a heavier cotton and spun poly thread because its silk-like finish acts almost like a lubricant, sliding nicely with the thread.