Magazine March 2015

Focus on the textile world: from maximum diversity to carbon fibers

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Sewing of leather

Tips for a perfect end product

Animal skin has been processed into leather since time immemorial. In ancient times its primary function was to protect people from the cold, but today, most of the world's manufactured leather is used in footwear production, or for applications in the automotive and furniture industry. However, as with all other materials, seams can differ. To obtain a satisfactory final product, it is very important to bear the specific properties of leather in mind during processing, and to select the most appropriate sewing machine needle in each case.

What is leather?

Leather is made from animal skins – specifically, from an animal's so-called dermis. This dermis has a grain side, which gives the leather its smooth surface, and a flesh side, which provides the mechanical strength.
Leather is a natural product, so it has individual characteristics. Every type of leather – according to the position of the animal's ribs – has a fiber direction in which it can be stretched better, but also tears faster. To create products that are as robust (i.e. as tear-resistant) as possible, therefore, processing should always take place counter to the fiber direction. All sections also need to be cut in the fiber direction, even though this procedure requires more material.

The durability of leather seams

When leather is sewn, the seam strength – that is, the durability of the seams – plays an important role. It is mainly influenced by the stitch rating, which corresponds to the number of stitches per centimeter. The higher the rating, the more threads the seam contains, and the higher the thread-related tensile strength of the seam. Maximum strength is obtained when a seam rupture (lateral load) breaks both the leather and the thread simultaneously. In order to achieve maximum seam strength, the stitch length has to be adjusted whenever there are changes in cutting point or thread parameters.

The durability of the seams is also affected by the tear strength of the leather: the larger the cut in the leather caused by the sewing needle, the lower the tensile strength. The needle thickness should therefore always be chosen so that the thread slides freely through the eye of the needle and there is sufficient stability for the sewing process. The selected needle should not be too thick either, to avoid excessively large stitch holes.

The correct point style

Since leather has a different structure in the longitudinal and transverse directions, sewing of leather with a cloth point - depending on the sewing direction – results in a different seam appearance. This is because hair and sweat ducts extend only in the longitudinal direction. To create a consistent seam appearance in all directions, the use of a cutting point is required.

Cutting points are available in many different shapes. In accordance with their geometry and orientation, a defined hole is cut into the leather, enabling the creation of various stitch formations (from straight to slanted) and seam appearances.

The selection of the right point shape depends not only on the desired seam pattern but also on the seam structure – as well as the nature and characteristics of the leather. The following general recommendations can be made:

Texture of leatherSeam designRecommended pointExamples of end products
Soft leatherLocking and clamping seamsNeedles with low cutting action (SD or RCar seats
Soft leather
(leather clothing)
Sraight seamsSDFine leather goods,
leather embroidery
Soft and hard leatherLockstitch seamsDepending on the desired seam appearance; LR-point most suitable for decorative effectsBags, leather clothing, shoes
Tougher leatherLocking and clamping seams in footwear (heel seams)P-point (stitch holes close under
seam load → high seam strength)
Hard leatherSignificant decorative effectsPBelts, upholstered furniture
Hard, thick and dry leatherStraight seamsDBelts, luggage, heavy shoes
All common types of leatherStraight seams with continuous closed appearanceLL or SBags, shoes
All common types of leatherMulti-directional sewingSD or RLeather apparel
All common types of leather2-needle decorative stitches,
slightly slanting seams
SAN® 12 LRCar seats, upholstered furniture, automotive interiors
Soft and medium hard leather2-needle decorative stitches,
straight seams
SAN® 12 SCar seats, upholstered furniture, automotive interiors

If leather is combined with other materials (e.g. in the automotive sector), the following recommendations apply:

Material combinationSeam constructionRecommended pointExamples of end products
Leather with foam laminationDecorative seamsLR, LL, S (depending on desired seam)Car seats
Leather with foam laminationClsoing seams and multidirectional sewingR, SD, RGCar seats
Leather / Synthetic LeatherDecorative seamsLR, LL, S (depending on desired seam)Car seats
Leather / Synthetic LeatherClosing seamsR, SD, RGCar seats
Leather / feltAll seamsD, DHAutomotive interiors
Leather / textile and synthetic leather / fabricAll seamnsR, RG, FFGCar seats

The GEBEDUR® needles developed by Groz-Beckert with their titanium nitride coating are also ideal for sewing leather. The extremely hard surface coating protects the looper point and protects the needles from wear and damage. This results in longer cutting edge service life and an overall increase in productivity.

Leather will always be a popular material, used in many areas. Whether for protective, professional or functional clothing, for accessories such as handbags, purses or gloves, whether in sport as a coating for balls and sports equipment, or as an indispensable material in the furniture and automotive industry – perfectly stitched leather will always find an application.

Would you like to learn more about the right needles and points for sewing leather? The Groz-Beckert experts look forward to hearing from you!