Needle thread meets bobbin thread. They grab each other and hold on for dear life.
When that relationship is perfect, as in 50/50, your machine TENSION is perfect. But like all relationships the balance can get out of whack.
You’ll know when that happens. Your stitches will be ugly, either all loopy or way too flat on one side or the other. You can probably pull a thread and pull the whole row out. This is a sure sign it’s time to adjust tension.
1) Step away from your project. Seriously. Even if it’s after midnight and you’re almost finished, don’t try to rush through a tension adjustment and risk wrecking your project.
2) Get out the machine manual, the lint brush, and a nice piece of cotton fabric to practice with. Use the brush to clear the thread paths of lint. Use the manual to make sure the needle and bobbin are threaded correctly. You may want to change the needle and/or thread. (Check out my recent post on why thread brands matter)
3) Lower the presser foot over a double layer of your medium weight cotton fabric and adjust the tension dial. (Make sure the presser foot is down when you do this.) If the dial is at three, turn it to 4 and try stitching. Keep testing and adjusting the dial until you stitches meet in a nice embrace.
Tension can be frustrating. You may have to step away and try again. You may need to wind another bobbin. Just remember to keep a cool head–like Mr. Inge, our expert sewing machine repair man who actually made house calls back in the day. He always walked in the sewing room, cut the scariest thread knots without fear. Then he put on a new spool and started fresh–no history, no cussing, no tears. My hero.