This document provides information about overlock machines, including their definition, uses, anatomy, selection criteria, and working mechanism. An overlock machine is a specialized sewing machine that produces overlock stitches to sew over one or two pieces of cloth. It is commonly used for edging, hemming, and seaming fabrics. The machine uses loopers rather than a bobbin to create thread loops that contain the fabric edges within the seam. Key factors for selecting an overlock machine include threading ease, tension control, presser foot design, and stitch width adjustment. The machine creates overlock stitches through the coordinated movements of the needle, upper looper, and lower looper.

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3. &
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4. Definition: An overlocked machine is a
specialized type of sewing machine that
produces overlock stitches to sew over one or
two pieces of cloth.
Uses:In most cases, overlockers are used for
edging, hemming, or seaming.
Working:Additionally, overlocker sewing
machines that come with built-in blades will
also trim off excess fabric along the edges to
prevent fraying.
How it differs from lockstitch:An overlock
sewing machine differs from a lockstitch
sewing machine in that it uses loopers fed by
multiple thread cones rather than a bobbin.
Loopers serve to create thread loops that
pass from the needle thread to the edges of
the fabric so that the edges of the fabric are
contained within the seam.
Speed:Usually run at high speeds, from 1000
to over 9000 rpm
Other names:Overlocking is also referred to
as “overedging,” “merrowing,” or “serging.”
Though “serging” technically refers
to overlocking with cutters, in practice the
four terms are used interchangeably.

5. ANATOMY
OF AN
OVERLOCK
MACHINE

6. of
SELECTION
OVERLOCK
MACHINE

7. • A two-thread model is best for finishing seam edges and decorative edgings, or finishing
edges for light fabrics. It can also be used to stitch flatlock seams. A flatlock seam is
usually sewn with the wrong sides of the fabric together. The seam is then pulled so the
seam allowances slip and lie flat inside the stitching. This seam is useful when seaming
sweatshirts, jogging suits, and other active wear made from sportswear fleece and velour.
It can be used to stitch elastic and lace to lingerie. Hems can also be sewn using some two-
thread overlock machines.
• Two-thread Overlock Stitch
• Used for finishing seam edges and decorative edges.
• Used for finishing scarf edges
• Should be avoided in areas that will receive stress.

8. • A three-thread overlock trims, stitches, and overcasts seams in one operation (Figure
2). The three-thread overlock seam is most useful when sewing knits. It can be used to sew
woven fabrics, but not in areas that will receive a lot of stress. The three-thread can also be
used to sew pin tucks, make narrow rolled hems, and to finish fabric edges. Decorative
stitches are possible using a variety of threads or yarns, such as crochet yarn, perle cotton,
buttonhole twist, lightweight knitting yarn, narrow ribbon, or metallic thread. Some three-
thread models can be converted to do two-thread stitching.
• Three-thread Overlock Stitch
• Suitable for sewing woven and knitted fabrics,but should be avoided in areas that will
receive stress.
• Can be used when sewing most shirts, blouses, skirts, dresses, lingerie, and swimwear.
• Areas of stress to avoid include crotch seam of pants and sleeve seams of shirts or blouses.

9. • The four-thread overlock will stitch a chain stitch or a safety stitch as it stitches and
overcasts seams (Figure 3). The chain stitch model is most useful when seaming woven
fabrics. The safety stitch model can be used to sew woven or knitted fabrics. It uses two
loopers and two needles. Some four-thread overlock machines convert to do three-thread
stitching.
•
Four-thread Overlock with Safety Stitch
• Used for same projects as the three-thread overlock stitch but can be used in areas that
receive stress.
• Suitable for sewing blouses, shirts, skirts, dresses, pants, lingerie, action wear, swimwear,
and sleepwear in knitted or woven fabrics.
• Four-thread Overlock with Chain Stitch
• Suitable when sewing woven fabrics, even in areas of stress.
• Stitch does not stretch, so should not be used in knitted garment when stretch is required in
seams.
• Used when sewing shirts, blouses, skirts, pants,
sleepwear, and draperies.
• Use chain stitch when fitting garments since
stitches are easily removed.

10. OF

11. There are a number of features to consider carefully when
selecting an overlock machine.
The major concern for prospective owners is the threading
process. Check to be certain the machine has a coded
threading—colors, symbols, or numbers may be used. The thread
stand should have adaptors for the use of cones or spools of
thread. Check the use and care manual for threading instructions.
The loopers are the most difficult parts to thread .
A special threading tool and a pair of tweezers are usually
provided. The lower looper is usually threaded before the upper
looper.
Types of Loopers
Eye Looper:interlocks with needle or looper thread
Blind Looper:doesn’t carry a thread of their own
Upper and lower loopers.

12. The tension dials may be marked with numbers to indicate
degree of tension, but some machines use + or − signs. The
tension system differs from machine to machine. On some
machines, tension dials are sensitive, requiring only a slight
turn to adjust the flow of thread. On others, dials must be
rotated several times before the thread tension is affected.

13. The presser foot of an overlock machine is much larger than
that of a conventional machine. The pressure on most
models can be adjusted to the weight of fabric being sewn.
Because the foot is so long, there is seldom a problem of
fabrics feeding unevenly as they are sewn. Check the
position of the presser foot lifter on the machine. On some
models, it is on the right side of the machine near the
handwheel.

14. The throat plate or presser foot will have a special stitch
former not found on a conventional machine (Figure 5). On
some machines, this former can be adjusted to change the
stitch width. On others, the throat plate or presser foot must
be changed when a different stitch width is desired. Stitch
widths range from less than 1 mm to greater than 5 mm.
Example of a stitch former.
Throat Plate

15. The stitch length adjustment procedure varies
from machine to machine. Some offer a stitch
adjustment dial on the front of the machine.
Others require adjustments to be made inside
the machine. Determine how easily this
adjustment can be made for regular seams or
rolled edges.
A power switch that turns the machine on and
off should be present. This switch may or may
not be connected to a light. A built-in light
should be included, if possible.
Although the cutting knives are made to last
for many hours of sewing, it is important to
determine how easy they are to change (Figure
6). One blade will need to be replaced more
often than the other; it is the least expensive of
the two blades.
Upper and lower knife blades and housing.

16. On some machines, the knife position can be
adjusted to vary the seam allowance width.
Some knives can be disengaged so trimming
does not occur.
Needles for overlock machines may be special
or conventional in design. Determine what
type is required and be certain they are readily
available. Be sure to select the correct size for
the fabric type being sewn, whether using a
special or conventional needle.
A variety of threads can be used on the
overlock machine. Standard threads can be
used for sewing regular seams. There also are
threads specially designed for these machines.
The overlock uses much more thread than a
conventional machine, so plan ahead. Cone
thread—more than 1,000 yards per cone—is
usually less expensive than regular sewing
thread. A low-twist nylon thread that allows
seams to stretch is also available.

17. Pneumatic Flat Cutter
• Sucks chain-off thread through a suction
opening which is located parallel to
throat to allow trimming.
• Trims chain-off thread produced on
double chain stitch side of safety stitch
machine
• Mainly mounted on safety stitch machine
Pneumatic Side Cutter
• Trims chain-off thread on side behind
presser foot.
• Cutter leaves shorter chain-off thread on
material
• Suited for blind hemming and serging.
• Mounted mainly on overlock machine.

18. Chain-off thread suction
• This unit sucks chain-off threads by
compressed air use.
• Also available in another type which
simultaneously sucks thread chips
produced after trimming.
Chain-off thread trimmer
• Used frequently
• Located at rear of throat plate
• Also known as GUILLOTINE TYPE.

19. SPECIAL
FEATURES
SOME

20. • Some machines have a variety of presser feet to help the sewer with special
needs.
• Feet are available for sewing a rolled hem and for applying elastic, cording, and
stay tape to seams.
• Blind hemmer feet may be available. The rolled hem may also require a special
throat plate.
• Take note of which come with the machine and which must be purchased as
extras.
• Other features to look for include an accessory or tool kit, a dust cover, a
carrying handle, a built-in accessory storage compartment, and a scrap catcher.
• Some machines have a base that can be adjusted to create a free arm for
sewing.

21. PROS-CONS

22. PROS
• Over lockers create an overlock stitch on edges
and trim excess seam allowance all in one-step.
These machines are fast as well. Most units sew up
to 1600 stitches per minute, which is almost twice
the speed of ordinary sewing machines. As a
result, an over locker is a real time saver.
• Over lockers provide a professional finish to your
sewing projects.
• These machines are excellent for attaching elastic.
• Over lockers provide versatile functionality. A unit
will offer functions for many other sewing tasks
such as decorative edging and rolled hemming.
CONS
• Learning to thread an over locker can be a bit
tricky. However, it does get easier with time and
practice.
• Over lockers are not stand-alone sewing machines
that can “do-it-all”. You will still need to use a
regular sewing machine for topstitching or
inserting buttonholes and zippers.
• In addition to owning a conventional sewing
machine, buying an over locker can seem to be an
extra expense.

23. WORKING MECHANISM

24. WORKING IN
DETAIL
• Gets drive from the electric motor which is
mounted in sewing table.
• The main parts of the sewing machine:
flywheel, main shaft, needle bar, loopers,
feed dog and presser foot.
• The flywheel is driven by motor connected by
belt and it drives the sewing machine main
shaft.
• Another end of the main shaft connects to
eccentric or cam, which drives the feed dog
(stationery) movement.
• The needle bar’s up and down movements
are controlled by a link mechanism driven
from top side of the main shaft and which is
synchronized with the feed dog movement
for every revolution.
• Other important mechanism used in the
overlock formation is loopers. There are
three important loopers, namely, top looper,
bottom and chain stitch loopers. They get
drive from the main shaft directly through a
link.

25. Needle bar
motions

26. THERE ARE TWO TYPES OF NEEDLE BAR
SET UP AVAILABLE IN OVERLOCK
MACHINE GENERALLY. ON STRAIGHT
NEEDLE MACHINE, NEEDLE BAR IS
GENERALLY LESS INCLINED BACKWARD
AT AROUND 20°–23° FROM VERTICAL OR
THE NEEDLE BAR IS JUST FIXED EXACTLY
PERPENDICULAR TO THE FEEDING
DIRECTION . IN ALL THE CASES, THE
MOTION OF THE NEEDLE IS IN A
STRAIGHT LINE.
IN ORDER TO FORM THE OVERLOCK
SEAM, THE LOWER LOOPER PASSES
BEHIND THE NEEDLE AND MOVES TO THE
RIGHT. THE UPPER LOOPER PASSES
BEHIND AND THE LOWER LOOPER
MOVES UPWARD, PASSING IN FRONT OF
THE NEEDLE.
IF THE NEEDLE MOVES UP AND DOWN
VERTICALLY, THE UPPER LOOPER WILL
NOT BE ABLE TO MOVE IN FRONT OF THE
NEEDLE, SO THE NEEDLE BAR IN THE
OVERLOCK MACHINE LEANS BACK AT AN
ANGLE TO PROVIDE ENOUGH SPACE FOR
THE WIDTH OF THE UPPER LOOPER
MOVEMENT.
THE NEEDLE BAR MAY BE ONE NEEDLE
OR TWO NEEDLE TYPE, IN THE CASE OF
2-NEEDLE MACHINE THE SPACES
BETWEEN THE NEEDLE IS AROUND 2
MM,2.5 MM OR 3 MM.

27. Looper moment

28. The lower looper moves under the fabric
from the left side of the needle to the right
side of the needle while passing behind the
needle. At the edge of the fabric, it crosses
the upper looper and passes it front.
The upper looper moves from the right end
of the fabric and it crosses the lower
looper.

29. Feeding Mechanicisms

30. The fabric is gripped between the feed dog and presser foot. It is fed a pre-
determined distance; this movement is a combination of vertical and horizontal
motion.
Feed dogs may be divided into two types. Single feed dog and double feed dog
system.
In the second type, one feed dog is in front of the needle and the other one
behind the needle. The choice is based on the application.
Differential feed dog is used for creating gathering or stretching of fabric as they
are sewn up under the needle.
For every 1 cm material feed, 2 cm of the material is delivered in the case of
stretch effect. This is generally used for the woven fabric.
In the other case every 2 cm of the fabric fed, 1 cm of the material is delivered
which gives an effect called gathering which is generally used in the knitted fabric.

31. &
USING
POWERPOINT
MACHINE
CHAIN STITCH

32. What is a Chain
Stitch
Machine?
A Chain Stitch machine a type
of sewing and embroidery machine used
to stitch looped stitches to form a chain-
like sequence. These machines are
commonly used while hemming or doing
embroidery on pieces of cloth. The
best chain stitch sewing machine will
ensure your designs have a creative and
unique touch.

33. OF

34. Single needle Chain Stitch Double Needle Chain Stitch
The machine then moves the
material forward projecting the
loop on the underside from the
previous stitch. The next drop
of the needle goes through the
previous loop. The circular
needle then releases the first
loop and picks up the new loop
and the process repeats.
It is made by first sending the needle down through the
material. Then, as the needle rises upward, the friction
of the thread against the fabric is sufficient to form a
small loop on the underside of the material. That loop
is caught by a circular needle which is beneath the
work.
It uses two threads. It is rarely used in today's
machines except for ornamental purposes
because it uses a lot of thread. It is found in
bulk material packaging, where it is used to
close big bags. In this case it is useful to allow
an easy opening of the bag.

35. of
EXPLANATION
TIMING DIAGRAM

36. 180 270 360/0 90 180
Top most position of
needle
Throat plate line
Top looper stitch formation line
Bottom looper stitch
formation line
Top looper stitch
lock
Bottom looper stitch
lock
Needle
movement

37. At 0°, the needle bar will be in
throat plate or base position.
The upper looper/first looper
will move forward (during the
movement from 0° to 90°)
and the lower looper will
move backward.
At 90° needle bar will be in
higher most position. The
first/upper loop will be in
throat plate/base position.
Second looper/lower looper
will be in backward position.
At 180° the first looper will
return, the first stitch/loop
will be formed, and the
needle bar will start moving
further down.
At 270° first looper will be in
backward position, lower
looper will move towards
(during the change from
180°–270°) and at 270°, it will
form the second loop/stitch.
At 360° after the stitch
formation, lower loop will
move back, and needle bar
will rise to its base/throat
plate position and the next
cycle will begin.

38. &
USING
POWERPOINT
MACHINE
FLAT LOCK

39. What exactly is
a flat lock
machine?
Flatlock stitching is the stitching that
looks like overlocking on both sides of a
seam and is often used in swimwear,
sportswear, on baby's clothes, or just as
a decorative exposed seam. It creates a
seam that is flat and has the same
appearance both inside and out.
Elements in Stitching
1. Needle
2. Looper
3. Spreader
(Multi needle machine may have more
than three needles)

40. Working
mechanism of
flatlock
machine
The flatlock sewing machine gets drive from the
electric motor which is mounted in sewing table.
The main parts of the sewing machine are flywheel,
main shaft, needle bar, loopers, feed dog and presser
foot.
The motion from the main shaft is directly connected
with the needle bar mechanism. A link from the main
shaft is taken to spreader mechanism with a cam. The
cam rotation is fixed as half revolution per every full
rotation of the main shaft. So that, the spreader
movement is controlled

42. Height of the
needle bar
• When the needle bar is lifted to highest
position, the standard setting between the left
needle point and the needle plate are as
follows:
• For 2-needle machine – left needle height –
9.3 mm (needle gauge –4.00 mm)
• For 3-needle machine – left needle height –
8.5 mm (N.G – 5.6); 8.1 mm (N.G – 6.4 mm)

43. How to adjust
needle bar
height?
To adjust the needle bar height, the face
plate is removed, and the needle bar
and cam connecter screw are loosened,
the height is adjusted as required and
the screw is securely tightened.

44. PRESSER FOOT
– LIFT HEIGHT
ADJUSTMENT
AND
PRESSURE
ADJUSTMENT
Lift height:
The distance between the bottom
of the presser foot and the top of
the needle plate when the presser
foot is in its highest position.
Pressure adjustment:
This can be done by moving the
pressure foot pressure regulator.
It can either be increased or
decreased on the fabric.

45. How to Adjust stitch length?
• Method 1:
Stitch pitch or Stitch length can be
adjusted by simply turning the stitch
dial(on the front side of the
machine) clockwise or anti-
clockwise.

46. • Method 2:
Push button is pressed first and
held; simultaneously the hand
wheel is turned to seek the position
at which the push button goes
further inside. With the push
button kept pressed, the hand
wheel is turned, and the required
scale is set matching with the mark.
Then the push button is released to
fi x the stitch length.

47. Adjusting the
differential feed
• The flatlock machine is also
provided with 2 separate feed
dog set up.
• The adjustment in the feed dog
movement will alter the feeding
ratio between the front and rear
feed dog

48. Positions of
adjustment
• If the distance moved by the differential feed dog is
larger than that of main feed dog, then the
movement is called as normal differential.
• When the reciprocating distance of the differential
feed dog is smaller than that of main feed, then the
feed system is called reverse differential
• The differential feed ratio is the ratio of the distance
travelled by the main feed dog to the differential
feed dog. If the main feed dog travels 3 mm and the
differential feed dog travels by 6 mm, the
differential feed ratio is 3:6, i.e., 1:2.

49. Feed dog position
• When the feed dogs are at
their highest point of travel,
there should be a distance of
0.8 mm–1.2 mm from the top
surface of the needle plate to
extended line ‘A’
• To adjust the feed dog height, the
screws 3 and 4 can be loosened
and the feed dog can be
adjusted.
• The alignment of feed dog can be
turned backward or forward by
moving the screw clockwise or
counterclockwise.

50. Needle to looper timing and setting
• During the needle insertion, the needle is inserted in to the groove to the maximum level.
• The distance between needle and the machine throat plate has to be checked every time. To adjust
the distance ‘a’ from the point of left needle to the top surface of the needle plate, the needle is kept
at the top most position. The distance varies from 7 mm to 8.2 mm based on the machine type.
• .

51. • The needle is kept at
the bottom position,
the looper screw is
loosened and manually
the looper is adjusted
to a position where,
the distance between
the looper tip and the
inner most needle (1)
of the flatlock machine
is approximately 3.8
mm (A) by adjusting
the screw at the
bottom of the looper

52. • When the point of the looper has
reached the centre of the left
needle from the extreme right
end of its travel, there should be
0.05 mm to 0.1 mm front to back
clearance between the left
needle and the point of the
looper. (During this travel, after
passing the centre needle to the
extreme right end, the right
needle slightly contacts the point
of the looper).
• The needle is allowed to lower
and move the bottom looper to
move to the extreme end of the
outside needle. The setting is
kept as such, where the distance
between the outside needle and
the tip of the bottom looper is
1.5 mm approximately

53. Top looper or spreader
settings
• To adjust the distance A from top surface of the
needle plate to the bottom surface of the
spreader (1), the screw 2 is loosened and the
height is adjusted from 7.8 mm to 9.0 mm based
on machine type and then the screw is tightened.
• To adjust the spreader front to back, when the
point B on the spreader comes close to the left
needle while the spreader (1), is being moved to
the left from the extreme right end of its travel,
the distance of 0.5 mm is kept from point B to the
left needle. This can be done by adjusting the
screw 2 and moving the 1 front and back.
• For left to right adjustment, when the spreader is
at extreme left end of its travel, there should be a
distance of 0.5 mm from the centre line of the left
needle point B on the spreader. Adjustment is
made by loosening the screw 3.

54. Thank You