Topic: Seam EngineeringBy Gaffer Talukder MANIK

Anatomy (Make-up) of a

sewing Machine

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Atanomy of Sewing machine

Seam Engineering

•It includes seam and stitch construction. •The more thread a stitch consumes, the greater is the strength!•This is clearly visible when we compare lock stitch and chain stitch. •Lock stitch is one in which thread is locked both sides of the fabric and starts with 301 lock stitch.

•It go through more shearing as compared to chain stitch and over edge stitch. •As in lockstitch threads are interlocked rather than inter-looped

Pin tucking Chine stitch shirring (Distribution)

a. Quality is the customers' perception (awareness) of the value of the suppliers' work output.

b. In manufacturing, quality is a practical explanation as the non-conformity of product ; it is also defined as fitness for purpose.

c. To Support personnel measure quality in the degree that a product is reliable, maintainable, or sustainable. A quality item has the ability to perform satisfactorily in service and is suitable for its intended (planned) purpose.

d. For the Textile & Apparel industry, product quality is calculated in terms of quality & standard of fibers, yarns, fabric construction, color fastness, designs and the final finished garments.

e. Etc..

Quality?

Defects

Fabric OZ/Sq. Yd. Grams/ SQ. Mtr thread Tex size needle Size

Ex. Light 2 -4 oz. 68 – 136gr. Tex 16, 18, 21, 24 60, 65

Light 4-6 oz. 136 – 204gr. Tex 24, 27, 30 70, 75

Medium 6-8 oz. 204 – 272gr. Tex 30, 35, 40 80, 90, 100

Med. Heavy 8 -10 oz. 272 – 339gr. Tex 40, 45, 50, 60 100, 110

heavy 10-12 oz. 339 – 407gr. Tex 60, 80, 90, 105 120, 140

Ex. Heavy 12 -14 oz. 407 – 475gr. Tex 105, 120, 135 + 140, 160

Related >> Fabric Weight / Typical Thread Sizes / Needle Sizes

Common Seam Example : All Types…

Stitch Type matrix PDF File

Needle Types PDF File

Decorative Stitch matrix

Common Seam Quality defects: Stitch Balance 301 lock stitch

DESCRIPTION: Where loops are seen either on the bottom side or topside of the seam. This is particularly evident with different colored needle and bobbin threads. Also, where the stitch is too loose.

SOLUTIONS: 1) Use a quality thread with consistent frictional characteristics; 2) Properly balance the stitch so that the needle and bobbin threads meet in the middle of the seam. Always start by checking the bobbin thread tension to make sure it is set correctly, so that the minimum thread tension is required to get a balanced stitch.

Poor Stitch Balance - Too Loose

Common Seam Quality Defects, Improper Stitch Balance - 401 Chain stitch

DESCRIPTION: Where the loops on the bottom-side of the seam are inconsistent and do not appear uniform.

SOLUTIONS: 1) Use a quality thread with

consistent frictional characteristics; 2) Properly balance the stitch so

that when the lopper thread is unraveled, the needle loop lays over half way to the next needle loop on the underside of the seam.

 Stitch Too Loose Proper Stitch Balance

Common Seam Quality DefectsImproper Stitch Balance - 504 Overedge Stitch

DESCRIPTION: Where the needle loop is not pulled up to the underside of the seam and the "purl" is not on the edge of the seam.

SOLUTIONS: 1) Use a quality thread with consistent frictional characteristics;

2) Properly balance the stitch so that when the looper thread is unraveled, the needle loop lays over half way to the next needle loop on the underside of the seam. 

Improper Stitch Balance Proper Stitch Balance

Needle Cutting on Knits

DESCRIPTION: Where needle holes appear along the stitch line that will eventually turn into a "run". Generally caused by the needle damaging the fabric as it is penetrating the seam.

MINIMIZING NEEDLE CUTTING ON KNITS:

1) Make sure the proper thread size and needle type and size are being used for the fabric

2) Make sure the fabric has been properly stored to prevent drying out and has been finished properly;

3) Check with your fabric manufacturer

Description: Where the stitch line is still intact but the yarns in the fabric have ruptured.

MINIMIZING SEAM FAILURES - FABRIC: 1) Reinforce stress points with Bartacks. Make sure the bartacks are the proper length and

width for the application; 2) Check to make sure the patterns have been designed for proper fit; 3) Make sure the ideal seam construction is being used 4) Contact your fabric supplier.

Open Seam Failure - Fabric Bartacks Used to Reinforce Fly Seam

DESCRIPTION: Where the yarns in the fabric pull out of the seam from the edge. This

often occurs on fabrics constructed of continuous filament yarns that are very smooth and have a slick surface. Also caused by loosely constructed fabrics.

MINIMIZING SEAM FAILURES - SEAM SLIPPAGE: 1) Consider changing the seam construction to a French seam construction;

2) Increase the seam width or width of bite; 3) Optimize the stitches per inch; 4) Contact your fabric supplier. 

Seam Slippage- Main reasons are…

DESCRIPTION: Where the seam does not lay flat after stitching.

SOLUTIONS: 1) If sewing machines are

equipped with differential feed, set them properly for the fabric;

2) Use minimum presser foot pressure during sewing; and

3) Observe operator for correct handling techniques. Too much stretching of the fabric by the sewing operator will cause this problem.

DESCRIPTION: Where the seam does not lay flat and smooth along the stitch line. Caused by one of the following:

1) Feed Puckering - where the plies of fabric in the seam are not being aligned properly during sewing;

2) Tension Puckering - where the thread has been stretched and sewn into the seam. The thread then causes the seam to draw back and pucker;

3) Yarn Displacement or structural jamming - caused by sewing seams with too large of thread that causes the yarns in the seam to be displaced, giving a puckered appearance.

DESCRIPTION: Where the edge of the seam is either extremely "ragged" or "rolls" inside the stitch.

SOLUTIONS: 1) Make sure the sewing machine knives are sharpened and changed often; 2) The knives should be adjusted properly in relationship to the "stitch tongue" on the needle plate to obtain the proper seam width or width bite. In the photo, the trimming knives have been set wider than the "stitch tongue" on the needle plate causing the "ropy" appearance.

DESCRIPTION:  Where a "joint" occurs on the stitch line. If this occurs on Topstitching, then the seam does not appear to be 1st quality merchandise. Caused by 1) thread breaks or thread run-out during sewing; or 2) cut or broken stitches during a subsequent treatment of the finished product (i.e., stone washing). 

MINIMIZING THREAD BREAKAGE: 1) Use a better quality sewing thread. This will help to minimize sewing interruptions. and/or  Minimizing Thread Breakage & Skipped Stitches

2) Insure proper machine maintenance and sewing machine adjustments; 3) Make sure sewing machines are properly maintained and adjusted for the fabric and sewing operation. 4) Observe sewing operators for correct material handling techniques. 

DESCRIPTION: Where the stitch balance is not properly adjusted (stitch too loose) and you can see the seam opening up. To check for Seam Grin, apply normal seam stress across the seam and then remove the stress. If the seam remains opened, then the seam has too much "grin through".

SOLUTIONS: To correct, readjust the sewing machine thread tensions so that the proper stitch balance is achieved. Too much tension will cause other problems including seam failures ("Stitch Cracking"), excessive thread breakage, and skipped stitches.

DESCRIPTION: Where the stitch length is inconsistent, possibly appearing as double the normal stitch length; or where you can see that the threads in the stitch are not properly connected together. Caused by the stitch forming device in the sewing machine missing the thread loop during stitch formation causing a defective stitch. On looper type stitches, this will allow the stitch to unravel causing seam failure.

MINIMIZING SKIPPED STITCHES: 1) Use a better quality sewing thread & Top stitch on the inside sewing allowance . This will include a higher performance thread designed to minimize sewing interruptions. 2) Insure proper machine maintenance and sewing machine adjustments; 3) Make sure sewing machines are properly maintained and adjusted for the fabric and sewing operation. 4) Observe sewing operators for correct material handling techniques. 

301 Lockstitch Seams For 301 lockstitch seams, Generally recommend using the same needle

thread size as the bobbin thread size in the seam.  Why?  Because “a chain is only as strong as its weakest link.”   

If a smaller, weaker thread is used in the bobbin, then the seam will only be as strong as the bobbin thread.  This is particularly true with lockstitch seams because of the way the needle and bobbin threads are interlocked together.

This does have exceptions.  Sometimes a smaller size thread with a different fiber type and/or thread construction can be used and still maintain seam performance.  An example would be to use a higher tenacity Corespun in place of a Spun thread.  To take this a step further, you can use an Anecord Nylon® monocord bobbin instead of a spun or corespun thread in the seam.  Also, exceptions can be made when a larger topstitching thread is desired to give a bold appearance on the outside of the garment when it is not necessarily being used to add strength or durability to the seam.

Common Seam Class Example : 400 & 401 lock stitch

504 Overedge Seams 504 Overedge seams have basically

the same needle thread formation as the needle thread on a 401 chainstitch seam.  Therefore, the same rule applies.  You can use a looper thread approximately 60% of the needle thread size without adversely affecting the seam strength (for example: T-24 needle thread – T-18 looper threads).  Just remember that smaller looper threads will not give the seam coverage of larger thread sizes.

Factors that Affect Seam Strength Five factors that determine the strength of

a seam include: Fabric type and weight. Thread fiber type, construction, and

size. Stitch and seam construction. Stitches per inch. Stitch balance.

DESCRIPTION: Where a tail of thread is visible on the topside of the button and when pulled, the button falls off.

SOLUTIONS: 1) Use a quality sewing thread to minimize skipped stitches; 2) Specify attaching the buttons with a Lockstitch instead of a single thread Chain stitch Buttons sewing machine.

STITCH ESTIMATING GUIDE:

1 square inch of “Fill” stitches at a normal density with a stitch of 6mm = 1000 stitches.  This is for a basic fill to cover an area with no stitching on top.

 1 square inch of “Fill” stitches at a normal density with a stitch of 4 mm = 1500 stitches.

This is for a basic “Fill” to cover an area that would have lettering or other stitching on top. The stitch length is shortened to prevent the stitches from pulling apart when the additional stitching is put on top.

DESCRIPTION:

Used to cover large areas. There are many different “Fill” stitch patterns and they can differ in direction, angle, and pattern. “Fill” stitches are used to cover large areas. (Also known as Tatami stitches.)  With today’s modern digitizing programs, there are many “Fill” stitch patterns that can be selected to give varying design appearance. Curved, fill stitches are becoming more popular in the industry. Using a “Fill” stitch in a curve can add more dimension to a design. This type of stitch is very useful for hair and water.

DESCRIPTION: Consists of forming three stitches between two points primarily used for outlining work. “Bean” stitches are more pronounced than Running Stitches.

STITCH ESTIMATING GUIDE:Triple Running Line (Bean Stitch) = 37 per inch

DESCRIPTION: Consist of a single line of stitching primarily used for outlining and detail work. They are also used as the foundation of most “underlays” and “Fill” stitches. Areas that are under 1mm in width are usually done with a running stitch.

STITCH ESTIMATING GUIDE:

Single Running Line = 12 per inch Double Running Line = 25 per inch (Normal Outlining Stitches)Triple Running Line (Bean Stitch) = 37 per inch 4-Ply Running Line = 48 per inch (Alternative to Satin Stitch

The friction between the needle blade and the fabric creates needle heat. The following factors can have an impact on the amount of heat that is generated:

Fabric thickness Fabric finish or density Fabric color or density (darker colors normally

are worse than lighter colors) Sewing machine speed Needle contact surface

Needle Size or diameter Needle length Type of needle blade Type of needle finish

Needle heat is usually more of a problem when sewing either synthetic threads and / or synthetic fabrics and can cause excessive thread breakage and / or damage to the fabric being sewn.

The thread characteristics that impact loop formation include: Elongation or stretchiness of the thread. Initial modulus or initial resistance to stretching. Twist direction & twist level. Liveliness of the thread. Frictional characteristics needed to set a balanced stitch

If the needle size - thread size relationship is improper, the thread will not be properly clamped on the scarf side of the needle and poor loop formation will occur. If the seam is not held in a stationary position when the needle is rising, the seam will rise with the needle and not form a proper needle loop. This condition, called flagging, is one of the most common causes of skipped stitches and thread breakage.

The physical properties in thread that impact how much the thread is stretched during the sewing process include:

Elongation properties of the fiber being used. Frictional characteristics of the thread needed to set a balanced stitch. Note: Regardless of the type of thread being used, as more and more tension is applied to

the thread, the thread will stretch more, affecting loop formation. Improper loop formation will result in a higher frequency of sewing interruptions. This is why it is recommended to always adjust the sewing machines thread handling system to sew with minimum thread tension.

Below is a recommended procedure for balancing the stitch on a any sewing machine: Set the bottom tension (bobbin or looper) to a minimum that still forms a consistent stitch. Reduce the needle thread tension until the stitch appears to be loose on the bottom side

of the seam then tighten the top tension until a balanced stitch is achieved.

Seam elasticity can be accomplished by a combination of having the correct number of stitches per inch and having the proper stitch balance. The more stretch the fabric has, the more stitches per inch that are required. Common ranges of stitches per inch are from 12 to 14 spi.

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