Depending on the type & thickness of material you will be sewing, the typical tension for a standard lock stitch Sewing Machine (Bobbin Case). Like an Industrial Juki DDL 8700 or Juki DNU 1541 You should try sewing on a scrap piece material that you will be sewing your product with. What you should be looking for is a uniform stitch top & bottom. Hiding the bobbin thread or knot in the thickness of material or the best you can. If the bottom of your material has bad tension it may look like a pretty straight line with a whole lot of dots.(Bobbin knot) That can be remedied by increasing upper tension until the bobbin knots gets pulled up into the center or thickness of material. The stitches on top & bottom of the material should look identical. If increasing upper tension does not seem to be adjusting the look of the stitches. It could be 1 of 2 issues,the discs on the upper tension assembly could have some residue or lint locked in between them causing the discs not to close properly or there might be too much tension on the bobbin case. Which can remedied by adjusting the tension spring on the bobbin case. Usually the larger of the 2 screws on tension spring. Small screw is the retaining screw & the larger one is the tension adjusting screw. Turn tension screw slightly counter clockwise (Very shallow screw so try not to turn it too much it will fall out) Until you find the right (uniform) stitch top & bottom. Then you can start sewing your products checking your thread tension occasionally to make sure you still have that happy medium. Like Arnold said I’ll be back..with more little sewing tips in the future. Thank You & I hope this little tip helped you out. 🙂
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