How to Adjust Thread Tension on Your Sewing Machine

Posted by Alfonsina Uriburu on

Both sides of the fabric should look great (hope that makes sense). On the front they look fabulous, but when turning them over the back could be very wonky. Using a sewing machine can be very simple knowing how to make basic adjustments to the tension setting to allow for proper stitching on different fabrics...

All machines have basically the four tension tools shown:

  1. thread guides,
  2. tension discs,
  3. tension regulator for upper thread,
  4. and bobbin-case spring for bobbin thread.

The tension discs and tension regulator together are called the tension assembly.

The tension discs squeeze the thread as it passes between them, while the tension regulator controls the amount of pressure on the discs.

The tension regulator is elementary: When adjusted to a higher number, the discs move closer together, increasing the amount of pressure. Turned to a lower number, the discs move apart, decreasing the pressure. 

The flat bobbin-case spring exerts pressure on the thread as it comes out of the bobbin case. The amount of pressure is regulated by a small screw at the rear of the spring. Both the spring and screw are easy to locate when the machine has a separate bobbin case.

When the machine has a drop-in bobbin with a built-in bobbin case, locating the tension screw can be more challenging. Both types are shown in the drawings below.

bobbin case tension

In either case, to increase the resistance, use a small screwdriver to turn the screw clockwise (to a higher number) or counterclockwise (to a lower number).

Turn the screw in small increments and never more than a quarter-turn between tests. This helps you keep track of how much you’re changing your settings and reduces the risk of losing this tiny screw.

Checklist before you adjust the tension

So many things can affect the tension before you reach for the tension regulator:

  1. Incorrectly threaded machine, use all thread guides. Sometimes using a big spool needs a stand holder.
  2. Incorrectly filled bobbin, evenly wound at the proper tension
  3. Dirty machine, between the tension discs, under the throat plate, or around the bobbin case and bobbin, increase the resistance and restrict the thread flow.
  4. Damaged or wrong size of needles for the thread you are using. A needle that’s too large or small for the thread can also unbalance your stitches, because the size of the hole adds to or reduces the total top tension.
  5. Incorrect sewing material, too many layers of fabric or too thin fabric for your sewing machine. 

Test basic adjustment

Select contrasting colors of a thread. Use one color to fill the bobbin, with the machine set on medium speed to reduce the risk of stretching the thread. Insert the thread the on machine, using all the thread guides on the machine head.

Set the upper-tension regulator at the middle of its range, and stitch a test seam on two layers of lightweight fabric, then examine the stitches.

Analizing the results...

  • When the tensions are balanced, the stitched line looks good on both sides of the fabric.
  • When the bobbin thread shows on the right side, the needle tension is too tight or the bobbin thread, too loose.
  • When the needle thread shows on the wrong side, the needle tension is too loose or the bobbin thread, too tight.

If the tension isn’t perfect, fix it by adjusting the bobbin spring; tighter if the bobbin thread shows on the upper layer, and looser if the needle thread shows on the underlayer.

Your machine is ready to sew!

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