7: Setting the Thread Tension
You have read the manual, selected and fitted the correct needle (see the blog article: Know Your Needles), selected the correct thread (see the blog article: Know Your Thread), wound, loaded and threaded the bobbin and threaded the needle, cut the fabric and are ready to start sewing. STOP!
Before you go anywhere near your cut pieces, you need to set up the thread tensions on your machine. Improperly set tensions are at the route of many sewing problems, so a little time take each time you use a different combination of threads and fabrics to set the tensions, the less time wasted unpicking a seam and potentially ruining a piece of fabric.
To set the thread tension, take two fabric scraps left over from cutting out, and in a combination that represents what you are going to ultimately sew, sew a straight seam.
What you are trying to achieve and invariably will not have is a nicely balanced seam, where the threads lie flat but are not so loose that you have loops or so taught that the fabric is puckering and where the interlinking of the threads is nicely balanced midway through the fabric, just as in figure 1.
In order to achieve the perfect stitch, you will need to adjust the upper and lower tension controls as described in the instruction manual and in the following manner.
If the tension is too loose and the stitches are forming loops, as in Figure 2, then both the top and bottom tensions need to be increased.
Too much tension
If the tension is too tight and causing the fabric to pucker up, as in figure 3, then both the top and bottom tensions need to be decreased.
Figure 3 : Too Tight
Bottom tension to high
If the lower tension is too tight, causing the interlinking with the upper thread to be exposed on the lower side of the seam, as in figure 4, then the lower tension should be reduced and the upper tension increased.
Top tension too high
If the upper tension is to tight, causing the interlinking with the lower thread to be exposed on the upper side of the seam, as in figure 8, then reduce the upper tension and increase the lower tension.
If, even after carrying out the adjustments described above, you are still unable to achieve a consistently good stitch, recheck that you have the right type of needle for the fabric type, the right size of needle for the thread size, then oth threads to make sure they are following the correct paths, pay particular attention to the spool and ensure that the thread unwinds freely without snatching in any way. Similarly, check the bobbin winding, and ensure you used the correct path, and that the thread unwinds freely from the spool when bobbin winding.