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[Wizcrafts]

Bob advised me to leave the bobbin tension alone...any adjusting should be done up top.....just an fyi....

This is only true when you keep the same size (and sometimes make and model) thread in the bobbin and just change thicknesses of material being sewn. If you change to a noticeably thinner or thicker thread, the bobbin tension can vary a lot.

At work, when I change from #138 to #69 thread (for garment leather repairs) I need to increase the bobbin tensioner and loosen the top tensioner. If the previous job used #207 thread, the tension changes are even more pronounced. Otherwise, I set the bobbin tension to allow the thread to feed smoothly, with some exertion, but not too much.

A very tight bobbin spring will cause the leather/material to have too much drag against the feed action. On thick leather this means shorter stitches than you might get otherwise. On thin or soft leather, that drag can cause the bottom thread to pinch the leather. Balancing an overly tight bobbin thread with more top tension may cause the thread to perforate the leather.

Finally, if the bobbin thread is very tight and you compensate by tightening the top thread, it makes it harder to remove the work when you are done sewing. You lift the pressor feet, with the foot lifter, but need to manually pull the threads backwards, to move the leather out of the machine. Sometimes the top thread will break from too much top tension, as you remove it.

If you have need of changing the bobbin spring tension often, make sure you use the proper size screwdriver, to avoid damaging the slot in the screw. Also, stick with one supplier of bobbins (assuming they don't give you any problems from the get-go). Manufacturing differences can throw off your adjustments, bobbin to bobbin. Nicks or bends on the end disks can cause the bobbin to drag at those points of rotation.

These are things I have learned while sewing on a 441 clone machine, into everything from 4 ounces of garment layer, up to 5/8" of veg-tan, and through 1/8" of ABS plastic when I'm repairing motorcycle saddlebags.Your milage will vary. We regularly use nylon thread sizes 69, 138, 207 and 277 with this machine. Our needle sizes range from #19 through #25. We mostly use #22 and #23 needles and #138 lubricated thread.