Next to fabric, thread is probably the item most consumed in the sewing process. Thread quality varies widely, and so do the prices of it. Unfortunately a lot of people compromise on thread to compensate for the amount of money that they have spent on their machine. This is a big mistake! There is a huge difference between thread that costs $7 per spool and thread priced at $1.99 per spool.
High quality thread will be smooth in appearance, with no “whiskers” visible when it’s held up to the light. Cheap thread often has slubs, or thick places where the fibers were not twisted tightly enough. As you sew this type of thread will shed fibers in one of two places. When used in the top of the machine it will pack up between the tension discs, forming a clump. This clump will prevent the discs from closing fully, resulting in loops on the bottom of the fabric. In severe cases it may be so bad that there is no top tension, making it impossible to sew without creating a bird nest on the bottom.
Cheap thread in the bobbin sheds fibers behind the tension spring in the bobbin case. Little by little the tension is reduced until you see bobbin thread coming up during embroidery. Fixing this leads to tightening the bobbin tension, which does little to correct the problem. Eventually the bobbin tension screw will be turned all the way down and it cannot be tightened any more. At that point it will be necessary to either clean the clot from the bobbin tension, or replace the case. In general dealers will opt for replacement rather than disassembling and cleaning the case.
Most dealers that sell thread will carry good quality products. Chain and “big box” stores will usually sell the lowest priced threads, which are also low in quality. Buying thread online may not always be a good choice. Many suppliers in Asia sell unbranded thread of varying quality, which online sellers can sell under their own label. Results will be unpredictable. You can usually rely on online opinions from Facebook, Pinterest, and other social networks. For any given thread brand, though, there will be some users who say their machine “hates” it, and others who claim it’s the only thread that their machine will sew with. Sadly many of the brands that previous generations sewed with have cut corners and quality to stay competitive. Using what your mother or grandmother used is not always a safe plan.
Metallic thread creates a different type of challenge to your machine. If your machine has a thread cutter, some types can get caught between the blades of the cutter and render it inoperative. In general it’s best to not use the cutter whenever you are using metallic thread. Needle threaders are also at risk when using metallic, as the thread tends to be heavier and harder to push or pull through the needle eye.
The worst offender for causing machine problems is monofilament thread. This may be sold as “invisible” or “clear”. It’s popular for any application where the stitches either should not show, or need to blend with two fabrics of different color. Nylon monofilament thread is essentially just a fine grade of fishing line. If it is really cheap, it may actually BE fishing line! This type of thread is very wiry and it has a memory of how it was wound on the spool. As a result, it wants to loop while sewing, which not infrequently causes it to come out of the take-up lever and start winding around the internal moving parts of the machine. That type of problem is difficult to repair, because a lot of parts have to be removed to get to the bind. If you have this happen more than once, don’t be surprised if your service technician puts up the “Closed” sign when you appear on their doorstep.