Gathering foot/ attachment for serger

I have a Bernina 800DL and am fairly new to using it.  I have the overlock of exposed seams down pat, but want to use my gathering foot and attachment.  I'd love to make cute ruffles for the bottom of the shirts I make my pre-schooler.  I can't get the settings on the machine correct.  Does anybody else have this model - or even a different one that they've successfully gathered on?  What did you need to do?

Love my ruffler. When I bought my new (second) serger, it was the first attachment I ordered. 

Here's what I do:
Increase the stitch length to 4.
Increase the differential feed to 2.
Increase the upper and lower looper tensions to 9.

You need to keep an even flow of fabric running through the serger with no hand tension on it or else it won't gather as neatly, often leaving gaps of ungathered fabric in the middle of your otherwise pretty ruffle.

Thanks for the tips.  I'll try it tonight and report back!  I want to make them correctly so badly...I can almost taste it, you know???