page title icon How to adjust the bobbin tension on a Brother sewing machine

A bobbin is one of the most vital parts of a sewing machine and its job cannot be done correctly without one. 

But what is a bobbin? Why is the tension important? What does it all mean? 

We’re here to answer all of these questions and to make sewing a breeze. Once we’re through with you, you’ll be ready to take on the world with your fashion creations.

What is a bobbin?

A bobbin is a small spool of thread. It is generally made of plastic, but can also be metal or wood.

The thread is wrapped tightly around the wheel many times and is attached to thin wheels at each end. 

Usually the bobbin is situated underneath the needle of the sewing machine. It is usually in a covered compartment you sew on top of. They are usually contained within a metal bobbin case.

When installing the bobbin in the bobbin case, it is important to ensure you are facing the thread in the correct direction, or the needle will not pick it up. 

The bobbin carries the lower thread up and through the material to catch the top thread. These combine to form a sturdy stitch to secure your fabric. 

Why is the tension important?

The tension dictates how well your stitches will secure your fabric. If the bobbin thread unwinds easily and the case falls out, your tension is too low. If the bobbin and thread do not move at all, your tension is too high. 

Incorrect tension can cause loose stitches or can cause stitches that are far too tight leading to the fabric wrinkling. If the tension is correct both threads will be incorporated into the material equally.

The stitches will be identical on both sides of the fabric and the location they combine and form a knot is hidden from view. 

Sewing tension depends on both the tension of the top and bottom thread, via the needle and the bobbin respectively.

Bobbin tension that is too low will mean not enough of the top thread is incorporated into the stitch. This can cause the fabric to pucker and you will begin to see the bobbin thread appear on the surface of the fabric.

Bobbin tension that is too high draws too much of the top thread into the stitch. This results in loose stitching and you will begin to see areas of the top thread appearing on the underside of the fabric. 

The bobbin tension is dictated by a single small screw on the bobbin case. This is combined with a small tension spring usually. 

You will need to adjust thread tension if you are changing the weight of the thread being used. Heavier (thicker) threads will need a lower tension setting than thinner, more lightweight threads.

If you are changing the material your thread is made of or even changing the brand of thread being used, you may need to adjust the thread tension on your sewing machine.

How do you adjust the tension?

To do this, you will need a small flathead screwdriver.  Only adjust the slotted head screw.

Do not use a Phillips screwdriver to adjust the corresponding screw on the bobbin case. This could cause irreparable damage to your bobbin case and make it unusable. 

You should remove the bobbin from the bobbin case before beginning to adjust the tension. 

To increase bobbin tension, turn the slotted head screw in a clockwise direction. A good estimate is a 30 to 45 degree rotation. Take care not to over-tighten the screw. 

To decrease the bobbin tension, turn the slotted head screw in an anti-clockwise direction. A good estimate is a 30 to 45 degree rotation. Take care not to loosen the screw too much.

The thread tension will be adjusted correctly when the upper thread slightly appears to be on the wrong side of your fabric.

If the upper thread on the correct side of the fabric appears to be looping or lifting off the fabric, but you cannot see the bobbin thread on the wrong side of the fabric, you need to loosen the tension.

If the bobbin thread appears in any way on the top of the fabric, you need to increase the bobbin tension.  

If you feel as though you need to force the slotted-head screw because it is so hard to turn, we suggest leaving it.

If you apply excess force in either direction, you could damage the bobbin case. A damaged bobbin case will not be able to keep the required tension while operating your sewing machine. 

If you cannot fix the tension easily by yourself, we recommend contacting the manufacturer or taking it to a professional repair shop.

What else could be causing problems?

Bobbin has been filled incorrectly

Before refilling the bobbin with a new thread, ensure all of the old thread has been removed, and rewind with consistent speed to maintain the tension.

Incorrect threading

Ensure the thread has passed through all of the thread guides on your sewing machine before it threads the needle.

Ensure the presser foot is down when you thread the needle to stop it slipping.

Damage

As sewing machines are delicate, any damage to the component parts can impact the tension.

Take care to dismantle and reassemble your machine carefully to avoid damaging it. 

Dust in the machine

If lint or excess fibers have built up on your machine over time, this can restrict the flow of the thread. They also increase the resistance the thread works against.

It is a good idea to periodically wipe down your machine with a lint-free cloth and check for blockages regularly. 

Change in needle, thread, or fabric

Variations in any of these categories can have an effect on the thread tension of your sewing machine.

Needle size creates holes in the fabric, and if the hole is too large or small for the thread this can throw the tension off. 

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