Satin stitch and zig zag the same?
 

Or is there likely a specific satin stitch on my machine?
The manual refers to it, but never says what number it is and I can't tell from the pictures so I'm wondering if it's just a zig zag.
I have Singer S18 (Janome 6500P)

Watson

I believe it is just a zigzag but spaced really close, like .2 or less in stitch length. And you might want to adjust the width to make it a little smaller.

I use a very tight zig-zag as a sating stitch. Found out that I get best results when I do a narrow path first and a slightly wider second path. When I only do one there are often gaps.

Yes, if you tighten up the zigzag you get the satin stitch. I know the Janome 6500 has that capability -- play with it a bit to figure out how wide and how tight works for your project. The Janome came with a foot that you could use when you do the ZigZag if your fabric is not heavy and you don't want it to roll - can't remember what the foot is called (DD has my 6500).

Also keep in mind a satin stitch tends to pucker your background fabric without some sort of stabilizer. I use the tear away kind.

Yes, a satin stitch is just a zigzag very close together. I never get a good satin stitch unless I use some kind of stabilizer. I also go over the satin stitch like Martina said. Sometimes I even do three passes if it don't get the coverage I want.

If you loosen your tension, you will also help with the puckering. I find a little experimenting often results in no need of a stabilizer with many fabrics.

I made my zig zag closer and find I have far better success than using the satin stitch. No idea why but I do the zigzag on all my machines.

It may also help to tighten the bobbin thread. That is recommended on some machines to keep it from showing on the sides of the satin stitching.

n

or loosen the top stitch a bit so it gets pulled to the backside of the stitch... It was also recommended to me to keep a separate bobbin for satin stitch rather than "play" with the sewing bobbin...just another thought