Understanding Sewing Machine Tension and Stopping a Big Ball of Thread on the Underside of Your Sewing.

Our sewing classes here in Colchester in Essex are as popular as ever. We cover such diverse topics as Patchwork, Machine Applique kids sewing project and how to set up a sewing machine. Okay that last one may seem pretty basic, you're reading a sewing blog so you know how to  set up your sewing machine. Well I'm not going to argue with you, however many people worry about tension without understanding it. To many people the tension dial is a piece of arcane technology who's method of operation has been lost in the dark winding passage of time. However I believe if you have even a rough guide of how this works you will become  a far more adept sewer.

A sewing machine works by sandwiching two layers of fabric between two threads which loop together in between the two layers of fabric. To achieve this all other cleverness has to happen, the teeth pull the fabric under the foot (which in turns hold's the fabric in place) and the teeth drop down to stop moving the fabric when the needle is down. As a tech nerd I love the ballet of mechanical cams that make all this happen in perfect time. So where does the tension come in? The tension controls how much of the top thread goes down with the needle. Different fabrics require different amounts of thread (due to how tight the weave is or how thick the fabric is). Sewing a simple test peice helps you work out how right or wrong your tension is.

In these examples the green thread is the top thread the red is the bobbin or bottom thread.

Normal Tension
  Here you can see the top thread on the top, and the bottom thread on the bottom, the threads over lapping in the middle of the fabric sandwich.  A good strong neat seam.

 Tension Too Low
As you can see from the underside view here the green top thread is forming loops on the under side of the fabric with the bottom thread just laying on the fabric. A terrible seam that will fall apart in moments

 Tension Too High
On this top view you can see the red lower thread showing on the top. Whilst not as severe as having the tension too low this does cause problems. The fabric can become puckered around the seam and even damaged.

 It's All About Balance
 The bobbin thread's tension does not get adjusted, it's constant. We adjust the top thread's tension to change the balance point where the fabrics loop together. However what if the bobbin tension was not constant, behold the shoddily wound bobbin on the right.

 The bobbin's tension is going "tight, lose, tight lose"  And so suddenly we get upper thread tying it self into a knot on the underside of the fabric as it's tension is relatively too high all of a sudden for a few stitches. Ever sewn and suddenly have a big ball of thread on the underside of your fabric fowling up your machine. This is what happens' the bobbin thread's tension is suddenly too high for the upper thread to cope with and too much upper thread appears on the underside, this get's caught in the guts of the machine and we get our dreaded thread ball!

How do we stop the dreaded thread ball?
Look at the pic on the right, look at all the technology being used to keep the upper tension even.   The lower bobbin tension is set as we wind the bobbin.

Now look at how we wind the bobbin, just a little circle of metal, that's all we get to even out the tension. IF you wind the bobbin at lightening speed or be going "fast, slow Fast Slow" you get an uneven bobbin. An uneven bobbin WILL give you a threadball on the underside of the fabric. And thus we come to the important point i make in EVERY lesson. Wind the bobbin slowly and evenly, it's an important job, not an afterthought. Pay more attention to your bobbin winding and I think you will find your sewing experience  improves no end.