Industrial Sewing Machine manuals

Knit fabrics stretch well, and woven cloth does not stretch. When sewing woven cloth and knit fabrics on the same machine, there is a tendency for cloth to shrink while knit fabrics stretch. For this reason, a differential device is provided on the machine (especially for knit fabrics).
An overlock has two feed dogs, one in the front and one in the rear.
The front feed dog is called the differential feed dog the rear feed dog is called the main feed dog. The rate of movement of these two feed dogs is adjustable. Woven cloth which tend to shrink require negative differential to be stretch sewn, and when knit fabrics which tend to stretch require positive differential to be shrink sewn.
※When the differential device is adjusted, the feed effect and the stitch length both change.

Always sure to adjust the stitch length after adjusting the differential.

Open the cloth plate and you will find the adjustment section. Make adjustments each time the fabric to be sewn is changed. This is something which you are responsible for adjusting, so learn how to do it well.
Loosen nut (1), move lever (2) up and down, and make either gathering or stretching adjustments. Fine adjustments can be made with dial (3).