I don't think I've every sewn on a single layer - alway double or with a stabalizer.

Get thee some stabilizer! You can find it at fabric shops and even Wal-mart. If you are doing machine applique, ask for a fusible stabilizer like Wonder-Under or Steam a Seam.

What type of cloth are you using, needle size, and settings are you using? I zigzag single layers all the time to finish seams and always do test runs first to find the best setting.

I'm thinking of hemming pants . Like to finish the edge with zigzag before I turn it up.
Claire

What, exactly, is your zig zag stitch doing? Is it tunneling? Is it disappearing into the hole in the throat plate? For the first, you may need to experiment with the upper tension (I don't advise messing with the bobbin tension)and/or the length/width of the zig zag stitch. For the second, sometimes a piece of tissue paper under the fabric will help and will tear off easily. If it's a cotton-type fabric, I've found that spray starch helps stabilize the fabric, too.

Mary