Long arm quilting machines require more adjustments to the thread tension than many basic sewing machines. Specialty threads for quilting come in many thicknesses and materials. Tension that worked for a polyester thread may cause cotton thread to snap. Long arm quilting machines adjust on the bobbin and the top thread. This helps you get the perfect stitch for many different threads. However, the tension screws are not marked as they are on other sewing machines, so a long arm machine takes special care to learn the tension adjustment.
Top Thread Tension Adjustment
Sew test stitches. The way the stitches form will give you an idea of how the tension needs to be adjusted. If loops form on the underside of the fabric, you most likely need to tighten the tension. If the top thread lies on the fabric and pulls the bobbin thread through all layers, you need to loosen the tension.
Mark your default tension setting. The top tension is adjusted by a knob on the machine. Long arm machines are not labeled like home sewing machines, so you may wish to mark your normal tension setting before changing it. Use a permanent marker and draw a small line or dot, then adjust the tension for you new thread.
Adjust the top tension. Turn the knob clockwise to tighten and counterclockwise to loosen. You may need to turn the knob one-quarter to one-half turn before you notice a difference in the test stitches.
Bobbin Thread Tension
Remove the bobbin from the machine. Most long arm machines have a removable bobbin case; when you take the bobbin out, the case comes out as well. Take this assembly out of the machine. Remove the bobbin from the case.
Clean the bobbin case. Use a small, stiff paintbrush to sweep away any lint in the case. This lint can cause the tension to tighten or interfere with the bobbin in other ways, so brush it all away.
Mark your default bobbin tension with a permanent marker before changing the tension. Use a flat-head screwdriver to change the tension. Like the top tension, clockwise tightens the tension. Loosening the tension requires counterclockwise turns. Only turn the tension one-eighth to one-quarter of a turn. Unlike top tension, a little goes a long way. If the bobbin thread lies on the fabric and the top thread shows on the bottom, loosen the bobbin tension and tighten the top tension. If the top thread is too loose or is looping, tighten the bobbin tension.
Thread the bobbin into the case as if you were about to sew. Drop test the tension by holding the bobbin case in your hand and pulling up on the end of the thread. The case should not lift off your hand more than a tiny bit. If it does, your tension is too tight. Once the bobbin and case stay on your hand and the bobbin unwinds rather than lift up, your tension is correct.
You can purchase tension gauges for your long arm machine. There are gauges for the top and bobbin thread tensions. These electronic devices measure the tension numerically. Jot down the numbers for the tension of your favorite threads so you can easily adjust to that number in the future.