Don’t be afraid to turn that dial!
The numbers on both the main tension and bobbin winder assemblies are not like the numbers on a normal home sewing machine as to where you can move the knob to a number and get a certain tension. On this system, the machine head is moved over fixed fabric that’s secured to a frame and the head is moved in all directions, therefore creating needle deflection and direction path of thread in the needle.
With the long arm machine, you have to find a ball park tension reference first and then use the numbers to fine tune the tension that you’re looking for. Basically, it’s a tug of war between the upper main tension and the bobbin case tension. On the upper tension assembly, the shaft that the white knob spins on are “fine coarse threads” and you’ll have to rotate that knob one to two full revolutions before you see any change in your upper tension. Once you see the change and you’re getting closer to the stitch you like, then use the numbers on the dial to fine tune that stitch.
With the bobbin case tension, turning that screw is totally different. The slightest movement will change the tension a lot. Most will move that screw in one hour increments. If you look at the tension screw on the bobbin case and let’s say the slot is facing at 12 o’clock and the other end is at 6 o’clock, to increase tension move it clockwise, move from 12/6 to 1 o’clock to 7 o’clock and check. If the bobbin case is too tight, then turn counter-clockwise to loosen.
If the top stitch has the bottom thread pulling up, most likely the bobbin case tension is to tight or not tight enough, loosen the screw one hour and check, if it’s getting better then loosen again or tighten, whichever is the case.
If the bottom thread is not being pulled up and you’re having eyelashes or railroad tracks, then tighten the white knob on the upper tension clockwise. Remember for both, right turns tighten and left loosen the tension.
I’ve found for most threads, (the higher quality threads) that when you pull both threads together after it’s threaded through the machine you should have the same tension when pulling. Sometimes, the upper thread will have a slight tighter pull but that’s rare but does happen.
As for the bobbin winder, adjust that white knob for the tension you like that bobbin to be wound too. This machine likes tighter wound bobbins compared to lose wound bobbins. If your bobbins are wound spongy, that is not good and you’ll have weak stitches. If your bobbins are too tight you’ll have problems. I wind mine to where the thread is firm and evenly spun. The tension of your bobbins will affect the tension of your machine head that we talked about above, so always maintain the same bobbin tension when winding your bobbins. Also, try not to wind bobbins while you’re sewing when your stopping and starting several times, this will create uneven tensions while filling up the bobbin.