Threads magazine has published a fantastic video that shows exactly what is happening when your machine takes a stitch. Check it out:
You also saw how the two threads meet perfectly right where the two pieces of fabric meet. The video shows perfect thread tension. But what if you have your top thread showing on the bottom of your quilt? Or your thread breaks? Or any number of issues?
Well, I've put together a tension issues flowchart that will hopefully give you some tips on how to solve your own tension issues. I hope you find it helpful!