I spent a good part of the afternoon watching the whole series. I know that Superior threads has been discussed here before, but these videos are really worth watching.
Tension, and why you shouldn't "ignore" it even on a machine that "auto" tensions:
http://www.youtube.com/watch?v=YzD-o...01QRL-QPUNrCbg
Bobbin Tension:
http://www.youtube.com/watch?v=Hf5dd...01QRL-QPUNrCbg
This video shows a visual of how the adjustment described in the video above works. (It's for a long arm, but the adjustment is the same.) At about 0:50 to 2:08 The most important part is that there are 2 screws, usually you'll adjust the "largest" screw, and it should always (in my experience) the one closest to the middle of the tension spring. The other one is just to hold the spring in place.
http://www.youtube.com/watch?v=TXJfT...01QRL-QPUNrCbg
Needles, this was enlightening to me. I guess I don't need all those little packets:
http://www.youtube.com/watch?v=Gaalv...01QRL-QPUNrCbg
The thread delivery system - I might know why spools sometimes jump off the op of my machines now:
http://www.youtube.com/watch?v=I1jq9...01QRL-QPUNrCbg
Thread Shelf Life:
http://www.youtube.com/watch?v=84Nrn...NrCbg&index=20
All of the "thread therapy" was worth watching actually. I learned a lot today.