I think QuiltnNan may have the answer. Tiny threads that get caught under the spring in the tension can cause havoc. Aargh, it's early morning for me and explaining anything is rough. Anyway, the idea is to gently insert a fine pin under the tension spring located in the bobbin case, sliding it to the end of te spring, gently checking for/removeing any threads or thread lint.

Somewhere on the Board is a wonderful explanation of how to check that your bobbin tension is right. Forgive me but I do not have the specific site at the tip of my tongue and today's project is an early leave time for a road trip to central FL. I'll find it when I get back if I don't see it on today's board.

Pat

The size needle hasn't much to do with the fabrics- the needle needs to be the correct size for the thread being used. Visit Superior Threads for free charts you can print that tell you what needle to use with which type/ weight threads and what the best application is.
Generally if your stitching is not good on the bottom your Top tension needs adjusting and if your top thread is breaking your Top tension might be too tight.
Clean your machine well, make sure the bobbin area is all cleaned up, oil if your machine is one you oil, rewind a bobbin, put together a small practice sandwich and see how it goes. Adjust your top tension a little ( loosen)
Sometimes the problem is the THREAD! When all else fails ( cleaned, I
oiled, new needle,( correct size for thread weight being used) , new bobbin) change the thread. It is always the last thing I try, out of frustration and 99% of the time fixes the problem.

I agree the bobbin tension is too loose. However, the needle tension could be tightened a tad also. That would balance the two tensions. I just "fiddle" around with the tensions until it gets right for me. Something my DH (who is a whiz with sewing machines) says is many times you have to work with the tension when you change to different materials, change thread or change needles.

Thanks for all the replies. There is much for me to learn.

When you wind your bobbins, keep you speed steady. Not too fast or slow. Medium speed and don't stop and go.

Thank you for saying that. That was my thought too, but wasn't sure. On my long arm, if the bottom thread is loose I tighten the top tension. I never mess with the tension on my Viking so wasn't sure it worked the same.

Bobbin tension should be loose not tight. It is your upper tension that needs adjusting.

I prefer an 11 or 12 for piecing quilting cottons. Most of the thread I have is "general purpose" and all my machines seem to do well with that combination.k

My machines are 30 to 60 years old. Don' t know about the newer machines.

I do use a "jeans/denim" needle for heavy fabrics.

This may sound dumb, but make sure your presser foot is down and your feed dogs are up. My stitches look exactly like yours when I forget to put the presser foot down.

That was my thought as well. There may me a piece of lint or a piece of thread caught under the bobbin case spring (that little flat piece that is held by the screw). I have that happen to me - and sometimes it is not obvious.

Here is a great article from Threads magazine - it may or may not be of help but worth the read!

http://www.threadsmagazine.com/item/...nsion/page/all