To increase the amount of fullness, tighten the needle tension 2-3 numbers, set the differential feed up to 2.0, lengthen the stitch length up to 4. Put your finger on the needle plate right behind the foot and let the fabric pile up on it as you stitch.
You can catch the needle thread (looks like a straight stitch on top or is straight in the thread chain) and pull on it to increase the fullness or redistribute the gathers.
Using the gathering foot, put the fabric to be gathered UNDER the foot with the right side up. Make a couple of stitchs on the fabric and raise the foot. Put the fabric it will be sewn onto into the slot on the foot with the right side down. Lower the foot and make a couple of stitches on that fabric. Guide the bottom fabric with your left hand and the top fabric with your right hand, making sure the fabrics stay even on the right side. To increase the amount of fullness, hold back slightly on the top fabric, letting more fabric feed into the ruffle on the bottom.
It's not the foot that makes the gathers, it's the adjustment of the stitches. You can make a ruffle with the regular foot. The gathering foot allows you to sew it onto something at the same time. Hope this helps.
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