SINGER 14T967DC-WORKBOOK QUANTUMLOCK - Manual (Page 71)

Thread Lower Looper with decorative overlock thread.
1. Raise the Presser Foot to release the tension disks. Thread the Lower
Looper as illustrated 1-10.
2. Pass thread from back to the front
through the thread guide .
3. Thread the top cover thread guide by pulling the thread towards the left until
it slips under the guide. Then pull the thread along the right side of the
button as illustrated.
4. While holding the thread, firmly pull the thread between the tension disks.
5. Turn the handwheel toward you until the lower looper extends 5-10mm
(approximately ½ inch) from the needle plate edge.
Three-Thread Overlock (wide-decorative) page 5