Differential Feed. You may have seen this term in your serger manual or printed on the face of your machine and wondered what it means. It’s one of the many features that distinguishes a sewing machine from a serger. First off, a serger has two individual sets of feed dogs unlike a sewing machine. They’re not side by side, but one in front of the other.
Differential feed adjusts the speed of the front feed dogs. This will affect how quickly the fabric being fed will reach the rear feed dogs. On BERNINA sergers, the differential feed knob is located on the side of the machine between the stitch length knob and the handwheel, but they can be in different places and not all sergers have this feature. Consult your manual to distinguish knobs. The speed settings have a neutral, indicated by N or 1, and go from 0 on up. Neutral has the feed dogs moving at the same speed. I’ll typically start here and serge a test swatch. This will give me a better indication whether to go higher or lower. Luckily it’s logical – the higher the number, the faster the speed. The lower the number, the slower the speed.
For example, on a lightweight fabric a faster speed will actually create gathers and a slower speed with can prevent unwanted gathering or puckering. Here you can see at the highest, neutral, and lowest settings.
On knits, serged seams have the tendency to ripple or wave. They’re not saying hi; the stretch of the knit is being stretched further. By increasing the speed, you’re reducing the wave. Be aware you can increase the speed to the point of slightly gathering so the highest, fastest setting may be too much. Again, always best to serge a test swatch first.
Mystery solved! Next time we’ll look at textured nylon thread and when best to use it. See you then!