I AGREE. The type of thread you are using on top or in the bobbin will vary. You just need to make sure your stitches are balanced. I have a Bernina 1530.

I work for a Bernina dealer. She has been the tech for over 40 years. Normally, you are told not to adjust the tension on the bobbin screw. However, recently a customer had purchased a pre-owned Bernina 730. She was in for her mastery class and had tension problems. The tech did take the bobbin case and test it with the weight. It still wasn't right and she brought me the little screwdriver and told me to adjust it 1/8 of a turn at a time until it looked right. She also told me the tension screw is set at the factory using 40 weight thread. Is it reasonable to think if you use a heavier or lighter thread it won't need to be adjusted? I won't be afraid to adjust mine when needed. I did so just yesterday ( I have a Bernina 440).

I have a 12 year old Bernina and I have never touched the bobbin tension or the top tension either for that matter.

I'm with you, repairs is how they make the their money. I say hogwash, too!

Just to add my 2 cents worth:

I have a 1530 and the only person who has ever changed my bobbin tension is a tech. That's not to say that if I was having trouble with that I wouldn't change it myself. If you use two different colors of thread (eg: black and white) in the top and bottom you should immediately be able to see if one side is looser than the other. You should never be able to pull either the top or bottom thread right out. Usually the only tension I have to change is the top tension and only by a little bit at a time. Remember this slogan: Righty tighty, lefty loosey. Your manual should tell you how to adjust your bobbin tension. I think the technician that told you that only a tech should adjust your bobbin tension is trying to drum up business for himself. After all, why would they show you how to do it in the manual, if they didn't think that the user of the machine shouldn't do it.

I also agree with the person who said to get an extra bobbin holder and never change the tension on that one. That way you always have a spare bobbin that has the right tension on it.

I have two older Bernina machines (130 and 153). I routinely adjust the top tension using the dial on the top of the machine depending on what types of top and bottom threads I'm using but I've never adjusted the screws on the "regular" bobbin cases. When I decided to try bobbin work using heavier threads and perle cotton, I decided to get what Bernina calls the "black latch bobbin case". It was pricey but it was an investment that has paid for itself many times over because I've never touched the tension screw on it either. I've found that the extra minute or two that it may take to make sure I'm using the correct bobbin case, have chosen the correct needle for the type of thread(s) I'm using, have checked the top tension adjustment, and have done some sample stitches have saved me a ton of grief over the years. If I find problems, most often it's because the bobbin has been wound "sloppy" for some reason, that I haven't been careful about inserting it in the bobbin case correctly and making sure everything is 'seated' firmly, or that the needle hasn't been inserted all the way or tightened down. Sometimes you have to take everything apart and go through this process "from the beginning" in order to find locate the issue -- and most of the time it's, uh, "user error".

Also....don't let the technician intimidate you!!!! I'd definitely want the bobbin case to simply be adjusted to "factory specs" and go from there.

Thanks for the website. I have ongoing problems with the tension setting on my Bernina 440 QE. I am going to buy an extra bobbin case just to play around with the tension settings. Maybe it will help make a prettier and straighter stitch. I have an old Kenmore that makes a straighter stitch with fewer problems.

Where I take my machine there is a 90 day warranty on their work, so if something is wrong/related during that time, I will not be charged a second time. So if there is bunching and maintenance was performed, she might not be charged for the return visit. I wasn't.