What causes railroad tracks?

September 24, 2013

These railroad tracks aren’t of the Amtrak variety … these tracks refer to those pesky “flat lines” of bobbin thread sometimes found on the back of your quilt. This sign of a tension imbalance actually has several causes. As you gain experience with your longarm, your quilts, and the threads you choose, you’ll be able to narrow down the culprit.

When the bobbin thread lies across the quilt back, the top thread isn’t doing its job of pulling the bobbin thread into the batting layer. The simple solution is to tighten the top tension until the railroad tracks disappear. However, depending on how tight your top tension was to begin with, you may experience top thread breakage before you successfully pull the bobbin thread into the quilt layers. When the top thread breaks, it has reached its “stress point.” That’s a clear sign that it’s time to also loosen the bobbin tension so that you actually still have “room” to make additional top tension changes.

Don’t be afraid to loosen the bobbin tension … sometimes a LOT. Even if your mother told you never to touch the bobbin case tension, we hereby give you permission to do so in your longarm! That larger screw on the outside of the bobbin case adjusts the bobbin tension. Use the “lefty-loosey (counterclockwise)” or “righty-tighty” (clockwise) theory to make changes. Adjust the bobbin tension in small increments.

Different threads, batting, and even fabric will require different tension settings. While devices that measure bobbin tension are certainly helpful, keep in mind that each quilt will present unique circumstances. Some threads will need tighter bobbin tension, while others will work best if the bobbin has nearly NO tension at all! You’ll get a gold star in your quilting handbook when you realize that:

  • It’s OKAY to touch the bobbin tension
  • Bobbin tension will be different for different threads and different quilts
  • Bobbin tension can be CORRECT when the bobbin zings to the floor, and bobbin tension can be CORRECT when the bobbin only drops a few inches
  • What works on your friend’s machine may not be the perfect setting for YOUR machine.

Many times simply loosening the bobbin tension (remember … it can have almost no tension and still be correct) will allow the top thread a chance to pull up the bobbin thread without even touching the top tension.

Railroad tracks also happen due to needle flex – something that happens with all sewing machines but is most noticeable with longarms simply because of the speed at which you move the machine. When the needle bends away from the hook (especially when moving to the left or away from yourself when viewed from the machine’s freehand side) the needle doesn’t have enough time to completely tug the bobbin thread up into the quilt layers before it must enter the fabric again. Railroad tracks are the result.

Since the tracks are also caused by needle flexing, these additional tips can help reduce that flex (and subsequently reduce or eliminate railroad tracks):

  • Switch to a larger needle
  • Move more slowly to reduce flex
  • Select a shorter stitch length to get the needle in and out of the fabric more quickly
  • Loosen the fabric tension between the rollers (tight fabric makes the needle bend more)
  • Choose batting with some “air space” to give the needle a fighting chance

Finally, even though your longarm machine can move 360 degrees across the quilt’s surface, it is still a “sewing machine”. Just as your sewing machine forms stitches slightly differently when you hold in your “reverse” button, the same holds true of a longarm. But because you can move the machine many times faster than you could ever hope to push fabric through a regular sewing machine, the needle flex and tension changes are also magnified. Try the steps above (especially getting comfortable loosening your bobbin tension) and you’ll soon be quilting with just about any thread imaginable!