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The Effect of Lockstitch Sewing Machine Processing Parameters on The End-Product Quality Part 3

Leather Sewing machine
Leather processing is one of the oldest crafts. However, production methods have changed significantly as also the requirements. In many cases today, good seam durability is no longer enough. The fashion industry also makes high demands on seam appearance. The objective is to create lastingly reliable connections that, wherever possible, also have a decorative effect, see figure (20). 15
Unlike old leather sewing machines, the machine head was remodeled to achieve an optimum balanced and highly rigid machine head frame. With its reduced vibration and noise and easy operation of the feed lever at the time of reverse stitching, the machine promises to make sewing work more comfortable. 

Machine parts:
It’s similar to the normal lock stitch sewing machine but some parts have been developed to be suitable for processing heavy fabrics such as Leather in order to achieve the optimum product quality in parallel with more professional industrial manufacturing. The leather sewing machine speed can be reach to 4000 rpm.

1)      Pressure Foot:
The roller pressure foot is the more suitable foot for processing the leather fabric as shown in Figure (21). In addition, it comes with two designs according to the manufactured product type. Therefore, the feed dogs have to change it’s shape according to the pressure foot attached to the machine. Machines equipped with 22 mm or 28 mm presser roller are designed for sewing leather and technical material products. 17

Roller presser is used for leather sewing. Rotating roller synchronizing with bottom feed instead of presser sole is located at the side of needle entry, and presses and feeds materials to be sewn. This can be called a kind of top and bottom feed. 13
The wider distance from the machine arm to the needle on the front of the machine head, smoothened design of the machine head, larger needle bar stroke (35 mm), and higher lift of the presser foot (13 mm up to 15 mm) enable easy handling of heavy-weight material. In addition, the machine is equipped with a hand wheel that is larger than normal for easy turning. 

1)      Stitch Length:
Like the same mechanism in the normal lockstitch machine, but it can be adjusted to a maximum of 7 mm(both in normal feed and reverse feed directions). The highly reliable and durable feed mechanism ensures accurate and consistent stitch length with no errors in the case of long stitching pitches. 16
2)      Needle Type:
As we mentioned before, that the needle size is affected by the weight of the fabric being sewn so the leather fabric has a special needle so that we can obtain perfect sewing for different leather products. The suitable leather needle is the cutting point one. There are various types of cutting point needle according to the type of leather product itself as shown in Figure (22 and 23). 

A study has analyzed the effect of two types of pressure foot with three different pressure levels on the sewing performance and quality as following figures (24, 25, 26, 27 and 28). It was concluded that Metal presser gives lower seam thickness, seam tensile strength, seam extensibility and seam appearance than plastic presser. In addition, It gives higher seam stiffness and seam pucker than the plastic one. Therefore, the plastic presser is recommended for better seam properties. There’s direct relationship between pressing level and (seam thickness, stiffness and pucker) as the press increases these properties increases and vice versa. Moreover, there’s inverse relationship between pressing level and seam tensile. Furthermore, the increasing of pressure enhances the seam pucker and appearance as well.

  2. GARMENT MAKING , State Institute of Vocational Education, Directorate of Intermediate Education Govt of Andhra Pradesh Hyderabad, 2005.
  3. STANDARDS OF QUALITY Copyright © 2008 by the Association of Sewing and Design Professionals, Inc.
  4. Studies on Seam Quality with Sewing thread Size, Stitch Density and fabric Properties. Sumit Mandal, The Hong Kong Poletechnic University, Institute of Textile and clothing, August 2008.
  5. Zorowski and Patel (1970), seam puckering
  6. Investigation of the Effects of Sewing Machine Parameters on the seam quality, Nagwa Ali Abou Nassif, Fashion Design Department, Design and Art College, King Abdul Aziz University, Jeddah, kingdom of Saudi, Life Science Journal, 2013;10(2)
  7. A study on the needle heating of industrial lockstitch sewing machine, Adnan Ahmed Mazari, Textile Technics and Materials Engineering, Department of Clothing Technology, 2015
  10. Textiles: Some Technical Information and Data IV: Sewability, Sewing Needles, Threads and Seams by L. Hunter and M.P. Cawood SOlrTH AFRICAN, WOOL AND TEXTILE RESEARCH, INSTITUTE OF THE CSIR, 1979
  12. Schmetz Needles , Herzogenrath, Germany, October 2006-10-22, Horst Gruchow, Technical Services Manager
  16. Juki sewing machine Catalog, DDL-8700L model, 1 needle lock stitch machine for leather and heavy fabrics.
  17. GF -111 Series leather sewing machine guide.
  18.  Effect of Sewing Specifications on Artificial Leather Seam Properties, Helwan University 2013