Seam Puckering refers
to the gathering of a seam either just after sewing or after laundering
causing an unacceptable seam appearance. Seam puckering is more common on
woven fabrics than knits; and it is prominent on tightly woven fabrics.
Puckering is usually
caused by one or more of the following conditions:
- Yarn Displacement
- Tension Puckering
(Excessive Thread Tension)
- Machine Puckering
(Uneven ply feeding)
Displacement or Structural Damage
Seam puckering is more
prevalent on very tightly woven fabrics because the yarns are oriented in
very tight layers that cannot shift easily to compensate for the thread as
it is inserted in the seam. This causes these tight yarns in the fabric to
draw up giving a rippled appearance along the seam line. This is usually
more of a problem when seams are sewn in the warp direction than in the
weft (filling) or bias directions.
Carefully clip the thread between adjacent needle penetrations along
the seam and observe if the puckering remains in the fabric or goes
away. If the puckering is still in the seam after the threads are
clipped, then yarn displacement is the probable cause.
to Puckering Caused by Yarn Displacement
To minimize seam
puckering caused by yarn displacement or the structural jamming of the
yarn in the fabric being sewn, do the following:
If a thread is sewn into
the seam with heavy machine thread tension so that it has been elongated
or stretched as the stitch is being set, the thread will try to recover or
return to its original length. This can cause the seam to pucker
immediately as the seam is coming out from under the presser foot;
however, sometimes the sizing or resins in the fabric will initially
maintain a flat seam but later in the day, the seam will appear puckered.
This phenomenon also occurs after the garment is laundered and the sizing
materials are removed causing the seam to pucker and the inspector to
think that there was too much shrinkage in the thread. Excessive thread
tension during sewing will not only cause puckered seams but also cause
other sewing problems including thread breakage and skipped stitches.
Carefully clip the
thread between adjacent needle
penetrations along the seam and observe if the puckering is reduced in
the fabric. If it is, then excessive thread tension is the probable
cause of the seam puckering.
to Tension Puckering
To minimize seam puckering caused by thread tension, do the following:
- Use very light
machine thread tensions. Begin by setting the bottom thread tension
(bobbin or looper) as light as possible but still maintain the
proper thread control. Next adjust the needle thread tension to a
minimum level necessary to maintain a closed seam and a balanced
stitch. This not only reduces the elongation of the thread in the
seam, but also improves loop formation and sewability.
- Use a thread with
a low elongation or high initial modulus to minimize stretching
during sewing. Use a thread with good lubricity characteristics that
will allow it to be sewn with minimum thread tension.
- Reducing the
thread size will not only help to minimize structural jamming but
can usually be sewn with lighter machine thread tension because a
smaller thread requires less tension to pull it up into the seam and
set the stitch.
- If structural
jamming does not appear to be a problem, increase the needle size or
use a needle with a ball eye needle to open up a larger hole in the
fabric so the stitch can be set with the lightest tension possible
- Properly set the
take-up spring so that the stitch can be set with minimum thread
tension. Polish or replace all eyelets and thread guides that may be
grooved to make sure they do not affect the frictional properties of
the thread. On some machines a rotary tension system is available
that meters the thread more uniformly that conventional tension disc
- On some machines
the thread control guides and eyelets can be adjusted to control the
thread more efficiently so less tension is required. This is
advisable when possible.
- On lockstitch
machines, make sure the positioning finger is correctly set to allow the
thread to pass through the hook with minimum resistance. If the machine
has a mechanical opener, set the opener to shift the bobbin case holder
so it will allow the thread to pass by the positioning finger with as
little resistance as possible.
- On lockstitch
machines, it is sometimes necessary to refine the gib or rail on the
bobbin case holder so the thread can be released by the hook sooner in
the stitch cycle. This sometimes allows the thread to be set with
- On most sewing
machines, four elements help in setting the stitch in the seam. They are
the take-up system, the feed system, the needle thread tension, and the
bottom thread tension. Proper feed timing in reference to the take-up
system is critical to sewing with light tensions.
- In extreme cases,
it may be necessary to use an oil free hook which uses at Teflon coated
rail. It has been found that machine oil migrates on other surfaces of
the hook and can increase the surface friction as the thread passes
around the hook.
- On 401 Chainstitch
machines, adjust the stitch balance so the needle loops on the bottom
side of the seam lay over at least half way to the next needle
penetration when the looper thread is unraveled out of the seam. The
looper thread must also be as loose as possible.
- Adjust the thread
controls to allow the stitch to be set with minimum thread tension. On
many chainstitch machines it is best to draw most of the needle thread
through the tension discs when the needle is rising, and a small
amount when the needle is descending (75% on upstroke & 25% on the
downstroke). Advancing the looper thread take-up timing will sometimes
allow the needle thread to be released sooner so that it can set with
lighter machine thread tension.
Puckering (Uneven Ply Feeding)
Feed puckering occurs when one of the fabric plies is fed into the seam at
a different rate than the other ply or plies. This causes a gathering effect
in the over-fed ply. Ply mismatching as shown in:
- Usually occurs when
the presser foot holds back on the upper ply as the bottom ply is being
fed into the seam at a faster rate by the feed dog.
- Usually occurs when
the operator holds back on the bottom ply and pushes the top ply into
the machine so the fabric edges will come out evenly.
Many seams observed
display both of these conditions, with the first usually contributing to
the latter because the sewing operator will attempt to correct for the
uneven feeding of the sewing machine.
Make two perpendicular
cuts across a sewn seam where the puckered condition is the greatest.
Remove the thread in the seam and see if the two plies are of equal
length. If one is longer than the other then the puckering is being caused
by uneven ply feeding.
Solutions to Feed Puckering
To minimize seam
puckering caused by uneven ply feeding, do the following:
- Use the minimum
presser foot pressure that will maintain uniform feeding. Make sure the
presser foot is clamping the fabric properly both in front and back of
the needle. When the feed is up and moving the fabric, the seam should
be clamped by the entire bottom surface of the presser foot. This can be
checked by inserting a piece of paper under the foot from different
angles and observing if the foot is clamping the fabric properly.
- Set the feed dogs
at their proper height and check for back-feeding. The feed dog should
have the optimum teeth per inch and number of rows of teeth for the
operation and fabric being sewn. Puckering can sometimes occur if the
material is not held down flat as it is being fed through the machine
creating a rippled appearance as the plies conform to the feed dog
teeth. Usually lightweight wrinkle resistant fabrics should be sewn with
feed dogs with 20 - 24 teeth per inch. Medium weight fabrics like men's
trousers should be sewn with feed dogs with 14 - 18 teeth per inch.
Heavy weight fabrics are usually sewn with feed dogs with 8 - 12 teeth
- Use the
correct presser foot and needle plate for the material and operation
being sewn. The needle plate and presser foot should have relatively
small needle holes in relation to the needle size being used. As a
general rule, the needle hole should be approximately twice the size of
the needle. Check to make sure that the needle plate is not bent down at
the needle hole.
- Use a low friction
presser foot: Teflon coated, roller bearing, "feeding foot", etc. Use an
"anti-puckering" needle plate with a retaining spring that holds back on
the bottom ply to match the top ply.
- Use machines
equipped with a needle feed or compound feed mechanism where the needle
moves with the feed as the fabric is being sewn. This "pinning" of the
plies as they are being fed helps reduce feed puckering.
- Whenever possible,
use machines equipped with auxiliary top feeding mechanisms such as:
walking foot, puller, top driven roller feed, upper belt feed, etc.
- On machines
equipped with differential feed systems, set the differential action to
slightly stretch the bottom ply to match the top ply so they are fed
evenly into the seam.
- Use automatic
machines equipped with material clamping systems that prevent the fabric
from moving as it is being sewn.
- Make sure you are
using the correct capacity of folders and guides for the fabric being
- Observe operator
handling for proper fabric movement to and through the machine.
- Make sure the
pieces are cut properly in the cutting room and the proper seam
tolerances have been maintained so the pieces are of equal length before
- If the plies have
different stretch characteristics, position the ply with the greatest
amount of stretch are against the feed if possible.