Singer QuantumLock User manual

Three-Thread Overlock
(Narrow, Wide, and Wide
with Decorative Threads)

Three-Thread Overlock (Narrow)
The Three-Thread Overlock Stitch is the most commonly used stitch because of
its versatility. It provides a wonderful professional seam finish to woven fabrics. It is
beneficial in preventing loosely woven fabrics from unraveling. In addition, the
Three-Thread Overlock Stitch offers unlimited decorative capabilities. It is
recommended for finishing seams but not reinforcing the seam. Use the conventional
sewing machine’s straight stitch to reinforce the seam. The stitch uses one overedge
needles and both the upper looper and lower looper. There are 2 different ways to set
up for a Three-Thread Overlock stitch. For a more narrow stitch (4.0) select the Right
Overedge needle; for a wider stitch (6.0) the Left Overedge needle is used.
Upper Looper Thread
Lower Looper Thread
Right Overedge Needle Thread
Three-Thread Overlock (narrow) page 1

ATD:
Auto Tension Dial
“A”
Left Cover Stitch
Needle “C”
Unthreaded and
Remove Needle
Middle Cover Stitch
Needle “D”
Unthreaded and
Remove Needle
Right Cover Stitch
Needle “E”
Unthreaded and
Remove Needle
Overedge Left
Needle “A”
Unthreaded and
Remove Needle
Overedge Right
Needle “B” (Blue)
Threaded
Upper Looper
(Green)
Looper Engaged
and Threaded
Lower Looper
(Red)
Threaded
Chain Stitch Looper
(Brown)
Unthreaded
Upper Knife Engaged
Seam Guide Plate Not Installed, use
Knife Cover Plate
Seam Width Dial “N”
Stitch Length Dial “2”
Presser Foot
Pressure
“N”
Differential Feed Dial “N”
Stitch Finger “N”
Spreader Not Used
Set-up:
Needle:
Three-Thread Overlock (narrow) page 2

The Three-Thread Overlock
makes a great edge finish to a
garment’s facing.
Three-Thread Overlock (narrow) page 3

Three-Thread Overlock (narrow) page 4
Turn Auto Tension Dial to “A”.
Turn Stitch Length Dial to “2”.
Engage Upper Knife. The knife will not trim the fabric when it is disengaged.
1. Open Looper Cover.
2. Pull the movable knife holder (silver screw) to the right as far as it will go.
3. Turn the holder clockwise until the knife clicks into a lock position.
Upper Knife EngagedUpper Knife Disengaged

Turn Presser Foot
Pressure Dial to “N”.
Turn Differential Feed
Dial to “N”.
Turn Seam Width Dial
to “N”.
 Set Stitch Finger to “N”.
Three-Thread Overlock (narrow) page 5

Install the Knife Cover.
Engage Upper Looper. Engaging the Upper Looper causes the looper move when
sewing. Even though the Upper Looper is not threaded it needs to be engaged.
1. Push the clutch button to the left and down to engage.
2. Turn handwheel.
Upper Looper Disengaged
Upper Looper Engaged
Three-Thread Overlock (narrow) page 6

Two-Thread Overedge (narrow) page 7
Disengage Spreader. The Upper Looper has a hole for the thread on the top of the
looper. If the stitch requires that the looper be engaged but not threaded, then the
Spreader is used. The Spreader simply plugs-in (or closes) the looper’s hole. The
Spreader is disengaged when the Upper Looper is engaged/operative and threaded.
The Spreader is used with a stitch that requires only one looper thread. With
the help of the Spreader, the single looper thread wraps around the fabric’s
edge.
1. Lower the white handle on the Spreader to open the eye of the Upper
Looper.
Thread Upper Looper with regular overlock thread.
1. Raise the Presser Foot to release the
tension disks. Thread the Lower
Looper as illustrated 1-9.
2. Pass thread from back to the
front through the thread
guide.
Spreader Engaged Spreader Disengaged
Eye of Looper

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”) from the needle plate edge.
6. Thread the looper area of the machine following the green color coded
thread guides 4-9.
Three-Thread Overlock (narrow) page 8

7. Thread the hole in the Upper Looper from front to back . Pull about 4
inches of thread through the looper and place to the back of the
throat plate.
Thread Lower Looper with regular overlock thread.
1. Raise the Presser Foot to release the tension disks. Thread the Lower
Looper as indicated 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.
Three-Thread Overlock (narrow) page 9