Q: Why does the feed dog drag and pucker the zipper tape?
The feed dog moves the tape under the needle, and a worn or badly set dog marks and stretches it. Looking at the underside of the seam first will show a row of tooth marks that points straight to the machine setting.
- Inspect the tape underside for a row of marks matching the dog teeth.
- Check dog height and whether it rises too far above the plate.
- Check that the dog is the correct type for the fabric weight.
- Sew a scrap at reduced pressure and compare the marks.
- Check whether the operator is pulling the tape, which increases dog pressure on the fabric.
Marks that match the teeth are a machine setting issue and are corrected by dog height and pressure, not by changing the zipper. If the tape is stretched rather than marked, look at operator feed and the differential setting before the zipper specification. Correct one factor at a time, because dog height and foot pressure interact.