I am still a believer in "don't touch the bobbin tension" IMHO it is very tricky to turn the bobbin screw and a little turn goes can make a really big difference in the bobbin tension. and then it is hard to get it back right.I am not aware that there is a special mark on the bobbin tension screw that will help you get it back to factory preset.so how do you know where you started. To test you machine tension- sew a live o the DIAGINAl on fabric. gently pull the fabric at both ends on the line and see if/which side breaks, If the top thread breaks then the top tension is too tight, if the bottom breaks the bottom tension is too tight, and is neither breaks then tension is good. I will try adjusting the top tension only first before messing with the bottom tension svrew.

The tension is the first thing I change on any machine I sew on, new or old. I start with 0 setting and move up 1/2 until I get the perfect stitch. You can't use the same tension with all the different type threads weights and needle sizes. And you have to adjust for weight and ply of bobbin thread. If a dial or button is on a machine it is there to be pushed or turned. Bobbin tension is not scary. Only if the bobbin thread is extra heavy do I have to change the bobbin tension on my machines.

I always heard that, too. When my machine started messing up I called the dealer/repairman, and he told me to adjust the screw – or bring my machine for a three-week sleepover, he was that backed up. He did suggest turning just a quarter circle at a time, which I did, and it was no big deal. It was nowhere near as fussy as I'd always heard it would be.

I never that term, I know from past experience, it is hard to get the tension perfect on 50s and 60s machines. Been there done that. I love my newer machines, much easier to sew on.

Well after over 60 years with sewing machines never heard this before. My mother and great aunt allowed me to pull their machines apart put together and fiddle with everything. As long as it was the same at the end as when I began. Even my father pulled clocks and bikes apart to put together. Later in life I did car engines myself then with very much younger brother. Never had a screw left.

Bernina 440QE
 

My Bernina dealer told me she didn't think I could get consistent stitches usinging King Tut 40/3 in the top and bobbin. She recommended if I wanted to try it I should buy another bobbin case. ($60). Because, she said, I should never touch the original factory bobbin case setting. Does anyone have experience with this? Is she just trying to sell bobbin cases? I'd like to believe that is not the case.

lots of info in the vintage sewing section: http://www.quiltingboard.com/vintage...s-t170748.html
I have found that the older machines and those plastic wonders seem to have a lot in common - user errors. That post is old but if you cut and paste some of the links will come up. There is other good info around, too.
User error: someone bought a couple vintage machines and left their 'old' plastic wonders with me. The only thing wrong with both plastic wonders was they both had the needles in backwards. Be sure to check to see what is really wrong with the machine. Someone else brought in a machine that he thought had a messed up tension. The pressure knob was set wrong and the feed dogs were slightly dropped. The bobbin tension was set wrong for the thread. If the tension isn't happy the machine isn't happy.

I always check the tension on a scrap of the fabric of the project before beginning piecing. The easiest way to see if it is right is to do a zigzag for about an inch and a half. When I bought my Pfaff 2044, I bought an extra bobbin case for those special thread stitches that need adjusting.

OMG - I thought I was the only one who grew up with "hands off the tension knob"!

Debbie

I'm very lucky and can go by this rule. I have a Viking Diamond Deluxe and it auto adjust so I've never had to worry about that. I know that if I use speciality thread that may change. I've used metallic and it did fine after I took it off the machine and put it in a coffee cup. Bottom line is; if the stitching/thread is messing up on the bottom of fabric it's your top area that has the problem rather its tension or rethreading, etc and if the messing up is on the top, then its the bobbin area which most of the time can be fixed by rethreading the bobbin, rewinding the bobbin or even cleaning it out. I try to make sure my top and bottom thread are of the same type and this helps eliminate problems too. I was told in class this weekend that all spool threads even the small ones should be used standing up. I've never had a problem with them laying down so she said I was lucky. It is another area that I can investigate when I have an issue so its good to know.