Did you ask him why? Is there some special tool that only techs have? Could you possibly mess something up by doing it yourself? Or do you have to pay a service fee every time you take it in to have the bobbin adjusted? If the answer to that question is yes, then I guess we know why he says a tech has to do it.

Personally I think it's hogwash. Check your manual to see if there are instructions on how to adjust your bobbin tension. I own several sewing machines; Brother, Pfaff, Janome, Singer, and I can adjust the bobbin tension on all of them.

I adjust mine all the time. Ask some of the sales ladies what they adjust their tension to - without mentioning the technician. I had a friend of mine just get hers back from servicing and was having issues. I had her loosen it some and no more problems. However note of caution -don't do it over a hard floor it can get away from you very quickly and if it lands on a hard surface you can get it out of round.

Yes it does sound too tight

Warning Warning - that is only for the Long Arm Bobbins not a domestic sewing machine - two different animals

OK so to confirm before I adjust the bobbin tension:

I have a Bernina 350. I plan to use the Bernina screw driver, and twist the screw on the bobbin to the left one click, IE going from 3 o'clock to 2 o'clock?

Then test it out, does this sound right?

NO! You should be comfortable adjusting your tension. That's why it's adjustable, so you can sew on cottons or Velcro, or double knits, or denim or whatever you want. I sent you a private message.

That's not true. Anyone can adjust tension on a bobbin case. It's not a skill. It's recommended to turn it one teeny tiny turn in one direction at a time then the other direction, until you get the stitch you want. Great info here:

http://www.superiorthreads.com/educa...sion-adjusted/

The best way I know to check stitches is to thread machine and bobbin in contrasting colors. Most of the adjustments I make on my Bernina 630E is simply with the tension settings. I have been told that the only changes to a bobbin must be very, very slight.

Lainey, This guy is having you on, or doesn't know what he's talking about. Do you have a manual? It should tell you how to take the bobbin and casing out, and which screw (if there's a choice) to turn to loosen it. The test you saw online is correct. Just unscrew a half-turn at a time till you're happy with the result.

The safest/smartest thing to do is buy a second bobbin case, imo. One that stays as the dealer adjusts and one that you use in cases when you want to adjust the lower tension yourself, for heavy bobbin threads for example. It not only maintains the dealer setting 'as is' on one, it also guarantees that you can still sew if you should happen to drop/lose the screw while adjusting the other.