Proper bobbin tension is essential to good embroidery. If tension is too tight, unwanted bobbin thread may begin to show on top of your garment and you may begin to experience frequent thread breaks which wastes time and money.
Bobbin tensions should be 18 to 22 grams (up to 25 grams when embroidering caps).
Proper tensions for satin stitches should reveal 1/3 bobbin and 2/3 top thread color on the underside of the embroidery.
If you are still experiencing bobbin thread on top of your garment after tensioning your bobbin thread, be sure that you are not using a damaged bobbin case, as this may cause undesirable results. Other factors can include improper top thread tensioning and damaged needles. Old needles may produce burrs and lead to frequent thread breaks.
Not sure how to tension your top thread? Read refer to the section on 'Upper Thread Tension'.