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Checking Bobbin Tension
To check or set the bobbin tension, remove the shuttle and bobbin from the machine. Tape 3 US quarters together (17 grams, 5.67 grams each) and then tape them to the end of the thread from the shuttle (thread must pass through the pressure point). (To get the thread into the pressure point, move the thread CCW around the opening between the bobbin and shuttle until it gets to the slanted slot in the metal; then pull it CW and the thread will slip down that slot to the circular section at the lower end. This will only make sense when you have the shuttle out and can see the slot ;-) Lift the shuttle up and note that this weight should barely cause the thread to move; adjust the screw as required to achieve this, then apply a dab of Loctite or nail polish to secure the adjusting screw. This 17 gram tension is much less than the 52 gram tension specified in the ULT Repair Manual but it is the setting on my ULT and on my Brother sewing machine too - I now suspect this low weight was using invisible thread in the bobbin but my machine's tension has worked well for me, with invisible thread and with Nebs and doesn't need adjustment when switching between them.
I repeated this experiment 10 months later and found I needed 5 quarters with Nebs, my machine's tension continues to work fine and I haven't changed any adjustments. The key point is to ensure the bobbin tension is in the ballpark by checking with a known weight (adjust as necessary if someone has gotten it out of range, then seal with Loctite or nail polish), then adjust the upper tension (via the knurled nut, see previous section) in sewing mode so the stitches look normal (no heads on either side); once this is done, embroidery tension should be correct with the tension on page 3 set to 4 -- at the very least, it should be possible to correct any embroidery tension problem via page 3 once the mechanical settings are correct.