Causes

Draglines are diagonal wrinkles caused by uneven feeding of the upper and lower fabric layer. They are prevalent when hemming rounded corners and thinner knits.

Fixes

Reduce presser foot pressure

Often, just reducing the presser foot pressure will vastly improve this issue. 

Baste the hem
Basting the hem before coverstitching is another effective way to keep the fabric in check.

Experiment with the differential feed

• Increasing or decreasing the settings can improve things, depending on how the draglines are formed. 

• Just experiment in small increments and see which option works the best in this particular case.

Draglines caused by the upper layer being pushed forward

Use an awl or another sharp object to gently push the fabric towards the presser foot in a rhythmic motion. This will ensure even feeding on both fabric layers. Just check that you don´t overdo it

Take the time to experiment and remember to document the settings in the notebook with the course once you find a combination that works. 

Summary

1. Start by reducing the presser foot pressure. This will fix the issue in most cases.

2. Baste the hem before cover stitching to prevent the upper layers from slipping 

3. Experiment with the differential feed settings and see if this improves the issue

4. Feed the upper layer towards the presser foot with an awl or narrow tool. Use slow rhythmic motions and make sure you still control the fabric so that it doesn’t slip.