by Carrie Schutrick

Created on: December 15, 2008

If you sew a lot, chances are good you've had an encounter with stitches that just don't work the way they're supposed to-huge loops on the back of the piece that get tangled in the bobbin, a needle thread that gets so tight it snaps, and so forth. Fortunately, the vast majority of these problems are simple to fix, once you understand what's gone wrong. That thing is almost always the tension.

To understand what tension is and why it's important, you first need to know how sewing machine stitches are formed. Unlike hand sewing, a machine's stitches are made of two threads, one from the needle and one from the bobbin; that's why there's a solid line of stitching on both sides of a piece of fabric. Ideally, the two threads interlock with each other precisely in the center of the pieces of fabric that are being sewn together. (There are special effects that use a bobbin wound with a heavy fiber that won't be drawn up into the fabric, but those are rarely used for structural sewing and involve deliberately screwing with the tension anyway.) Without proper tension, the interlocking doesn't happen right, leading to those huge loops on one side or the other of the fabric; if the tension is just too tight all around, the thread can't stand the extra strain and snaps. So there's a happy medium in sewing machine tension.

First thing to do is diagnose the precise nature of the problem. If you're getting big loops on the underside of the fabric, the tension on the needle thread is too loose, causing it to be pulled down by the bobbin thread. If the loops are on top, the needle thread is too tight (this is less common than the other problem). And if the threads are snapping, but make balanced stitches when they don't break, both the bobbin and the needle threads are too tight.

Once you know where the problem is, all you have to do is find the tension knob. The one for the needle thread will most likely be immediately above and to the right of the needle, and generally conveniently marked with something to tell you which way to turn it to tighten or loosen. Playing around with it to find the tension that will give you balanced, properly-interlocking stitches should only take a few moments.

If your problem is the thread snapping, you might have to adjust the bobbin tension as well. This is a little tougher, as you're supposed to leave it alone, but if you're up for a little adventure you can probably find the screw that adjusts it. You'll need a very small screwdriver, and try to make only very tiny adjustments.

Look for tension problems especially when you've just changed the weight of the thread or fabric you're working with. If you almost always sew quilting cottons with all-purpose thread, you likely won't have to adjust the tension very often (though the vibration of the machine working can sometimes throw it out of whack). It's when you change things that issues happen, so always try a new thread and fabric combo on a scrap before committing to an actual seam, especially if the fabric is something that will be hard to rip a seam out of neatly.

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