This tip is on How to adjust thread tensions. Otherwise known as "Why is that screw loose on my bobbin case?”

First things first. Most sewing machines are capable of forming a consistent stitch. The tensions on a machine are only one component to help achieve this. Inconsistent stitching is usually caused by something other then a tension imbalance, such as burrs on the hook or bobbin case, or a snagging thread supply. Did I mention that The Universal Thread Holder is designed to be a snag free thread stand? Did you get yours yet? If not, you should do that now. Go ahead, I’ll wait…..

So now, within a few days, you will have eliminated the possibility of a snagging thread supply causing inconsistent stitching. A consistently bad or loose stitch can be a tension problem. It can also be attributed to feed timing or thread clearances. See, and you always blamed that poor tension! Assuming everything else is OK, lets get back to the tensions.

Lint buildup in the tension discs   Lint buildup in the bobbin case tension

The tension is usually created by squeezing the thread between two polished metal discs (top thread) or pinching it under a polished piece of spring metal (bobbin thread). Make sure nothing is stuck in there where the thread normally goes. If there is a piece of fuzz or lint stuck in there, it prevents the tension from squeezing on the thread. This is more common then you might think, and can be avoided with a couple of tips. Always cut the thread cleanly before pulling it out of the bobbin case or unthreading the upper tension. Also, always raise the presser foot to release the upper tension before pulling the thread out. The fuzz or lint buildup is usually caused by tiny bits being pinched off of the end of the thread when pulling it through.

The goal is to have a balanced stitch, where the bottom stitching looks the same as the top stitching. Or at least, very close to the same. The following picture shows two rows of zigzag stitching. This is a bottom view. The first row is balanced and the second row shows an imbalance. You can see a great deal of upper thread pulling down to the underside of the fabric. Notice how consistent it is. Now, there were some early machines that could not do much better then this, but that’s a whole different story. This imbalance would indicate either not enough top tension or too much bobbin case tension.

Bottom of fabric - Top row OK - Bottom row tension imbalence

The first thing I would suggest is to increase the upper tension a little bit. If this solves the imbalance, put away your tool kit and call it a day. If you have to increase the upper tension way above “normal” then the bobbin case tension needs attention. Return the upper tension to it’s “normal” “auto” “standard” “regular” “whatever” setting. Numbered tensions will usually be between the numbers 3 to 5. For the lower row of stitching in the above sample, the bobbin case tension would need to be loosened. How much? Well, to get technical, just a smidgen. Small changes in bobbin case tension can cause large changes in stitch appearance. This is why most tension adjustments should come from the top tension. At least it is numbered and repeatable. The bobbin case tension is meant to remain constant.

Another tip. Do not remove / loose the bobbin case tension screw. Most sewing machine stores do not stock the wide variety of different bobbin case tension screws. You would usually be required to purchase a completely new bobbin case.

One more tip. Embroidery machines usually use thin bobbin fill threads. These thinner threads create less tension in the bobbin case, causing the bobbin thread to pull up to the top of the fabric. If loosening the upper tension somewhat doesn’t alleviate the situation, increasing the bobbin case tension will. Again, usually just a smidgen should suffice.

Sew, lets recap. If the top thread is pulling down to the underside of the fabric, increase the top tension. This will pull the stitch back up into the fabric. If the bobbin thread is pulling up to the top of the fabric, loosen the top tension and the stitching will drop back down into the fabric. If the bobbin case tension needs adjusting, start with the upper tension at it’s “normal” setting and either increase the bobbin case tension to pull the stitch down into the fabric, or decrease the bobbin case tension to allow the stitch to be pulled up into the fabric. And to help with a consistant stitch, nothing beats a snag free and tangle free thread supply, like The Universal Thread Holder.

And if all else fails, well, that’s what service departments are made for.

Happy Sewing


RJS Designs Inc.   Saint Petersburg, Florida USA