SEAMS & STITCHES
A seam is a joint consisting of a sequence of stitches uniting two or more pieces (layers) of material(s). A seam line is the stitched line or a seam that is usually parallel to the raw edge of fabric. Seam line is always at a specified distance from the raw edge of the fabric. A seam allowance is the distance between the seam line and fabric edge.
Seams are used for assembling parts in the production of sewn products. As there are numerous types of seams, there are 2 commonly (British and the Americans) prevalent systems of classifying seams. In each system of classifying seams, a class of seams is designated with symbols and names for easy recognition. Either American or the British way of classification is followed as a STANDARD all over the world.
Each seam representation consists of numbers, symbols and alphabets.
- CLASS – Based on the way fabric layer are arranged, Seams are classified into CLASS from 1 to 8.
- SYMBOL – each horizontal line represents one layer of fabric. Each vertical line running across the fabric line/s represents one sewing line.
- ALPHABETICAL NUMBERING – In American representation, Alphabetical numbering is used.
CLASSIFICATION OF SEAMS
- Superimposed seams – used on side seams of shirts, blouses, skirts, jeans and trousers, collars and neck lines. Superimposed seams are formed by sacking or superimposing fabric plies. The edges are evenly placed one over the other. The plies are then sewn together. The sub categories of superimposed seams are Simple, French and Piped.
- Lapped Seams – the most secure of all seams. Lapped are seams where the fabric plies are stacked or folded into one another. The raw edges do not align over one another, but are spaced. Used in sails, leather garments, casual shirts, yokes, pocket openings, welts.
- Bound Seams – bound seams are made by using a fabric strip to cover raw edges on main fabric. Bound seams are used at necklines, hems, any other edges of a garment.
- Flat Seams – folded or unfolded raw edges of fabric are placed beside each other and stitched. A wide type of stitch (e.g.…zigzag) to hold fabric layers beside each other. Used mostly on knitted fabric and to reduce thickness/heaviness of seam.
- Decorative Seam – Used to make pin tucks or to apply laces or tapes.
- Edge Neatening – Either fabric edges are folded on to themselves and stitched or another piece of fabric is applied (not covered) over the edges of fabric and stitched. E.g... Shirt buttonhole, over locking of single layer fabric edges, Pico of sari or dupatta edge, garment hems are examples of Edge neatening.
- Class 7 – in this class, an additional item like elastic or interlining are added to seams to stabilize shapes. E.g... Inserting elastic at waist bands or using fusible interlining between layers of cuffs to attain a neat corner shape.
- Class 8 – Seams that help in making a complete garment component. E.g... Fabric belts or Belt loops.
Seam Types matrix from A&E seam_type_matrix_flyer2.pdf
Stitches are formed by one unit of conformation of thread resulting from repeated passing of a strand or loop of thread through a material at uniformly spaced intervals. For the thread to penetrate through fabric, a needle pierces the fabric and creates space. Stitches are used to hold layers of fabric together or in place.
Stitches can be formed in 2 ways – interlacing of threads or inter-looping of thread.
Interlaced stitch formation is known as LOCK STITCH. Inter-looped stitch formation is known as CHAIN STITCH.
Lock Stitch formation 2-thread Chain Stitch formation
Stitches are classified into 6 standard classes:
- Class 100 – Chain stitches – used as decorative stitches
- Class 200 – Hand stitches – used as decorative, functional or temporary stitches
- Class 300 – Lock stitches – Most stable and strong of all stitches, very commonly used.
- Class 400 – Multi thread Chain stitches – Second most frequently used stitches. Are strong and stretchable.
- Class 500 – Over edge stitches – Highly elastic, do not unravel easily used in covering edges of fabric seams.
- Class 600 – Cover stitches – Webs of stitches form over the surface of fabric, extremely stretchable. Stitch web is formed on both (right and wrong) sides of seam.
Download Stitch types matrix from A&E Stitch-Type-Matrix.pdf
FACTORS CONTRIBUTING TO NEAT STITCH FORMATION
Stitches are considered NEAT when the structure of the material is distorted to the least possible extent during stitch formation. A correct balance of the following factors is required to form neat stitches.
- Fabric weight & thickness
- Sewing Thread type & denier
- Thread tension
- Seam Type
- Needle type and size
- Type of Needle point
- Feed Mechanism of Sewing Machine
- Stitch density and length - SPI (stitches per inch)
SEAM AND STITCH CHOICE CRITERIA
Seams are chosen based on the following criteria:
- SEAM POSITION: Position of seam on garment. E.g... Side seam, arm hole, placket, pocket application, hem, neckband attaching, fly etc….
- FABRIC WEIGHT AND QUALITY: The fabric and other materials, their thickness, inherent elasticity of each fabric/material. E.g... Twill cotton trouser fabric is heavier and firmer than twill cotton shirt fabric. A knitted fabric of any weight is always more elastic than a woven fabric made without spandex / elasthane / Lycra content etc...
- DURABILITY: Expected life of garment. The seam is expected to hold as long as the garment is in use. Garment life is gauged based on the number of domestic washes it has to withstand – 10washes, 20 washes, 50 washes etc... Longer the life of the garment, stronger the seam has to be.
- COMFORT IN WEAR: Seam should not inconvenience the wearer by either cutting into their skin or by rubbing/pricking against skin. This is a consideration especially in close / snug fit clothing.
- SEAM STRENGTH: When under stress during use of garment (seams are stretched during physical activity) seams should not split or slip or break.
- STITCH TYPE: The type of stitch that needs to be used for specific fabric qualities also determine or limit the seam types that may be used. E.g.… Knit fabrics, as knit fabric has inherent elasticity it stretches easily, chain stitch is used for sewing and lapped seams cannot be used due to their rigidity.
- ELASTICITY: There has to be inherent stretch in the seams to accommodate slight stretching of seams during physical activity of the wearer. E.g.…. Underarm seams have to stretch when arms are moved.
- SECURENESS: Seam should not unravel easily. Stitches should not untie or break or open easily. E.g... Chain stitches unravel easier than Lock stitch. Chain stitches have to be locket with bar tacks at the start and end.
- USAGE: Daily wear and tear on garment and also the type of industrial and domestic washing the garment undergoes in its lifetime.
- ECONOMY: The time taken to make the seam and stitch and also the labor cost for the type of seam and stitches along with the cost of machines and equipment required to make the particular seam and stitch are a factor to be considered.
- AVAILABILITY OF MACHINERY, EQUIPMENT and MANPOWER: To be able to make a particular type of seam and stitch, specific machines and equipment are required. Equally important are the manpower able to use these machines and equipment. When any one of these 3 is unavailable, compromises are made.