Classification of sewing machine

Sewing Machine

A sewing machine is a mechanical (or electrical) device that joins the fabric, using thread, in a way similar to manual sewing machines. Sewing machines make a stitch, called a sewing machine stitch, using between one and four stitches. They include means of gripping, supporting and transporting the fabric past the sewing needle to form the stitch pattern.

Classification of Sewing Machine Based on its Bed Type

Classification of Sewing Machine based on machine types

Different types of Feed Mechanism in Industrial Sewing Machine

Feed systems, feed types and feed mechanisms are terminologies used in various kinds of literature interchangeably. In sewing machines for the manufacture of fashion and commodity apparel, the universally used feed system is called drop oscillation feed or simply drop feed from the bottom, which accounts for more than 90 percent of sewing machines installed in factories. The machine parts responsible for supporting from the bottom drop oscillating feeding dog and belt while the parts responsible for feeding on the top are needle, puller, rotary presser foot, walk (oscillating) teethed presser foot and belt. Sewing machine types of feed are numerous, they are given below.

Drop Feed (Bottom Feed) Sewing Machine

The three parts of the sewing machine that together constitute the drop-feed mechanism are foot presser, throat plate, and dog feed. The feed dog feeds the fabric from the bottom in a drop-feed system, while the needle is up (Figure-1). Since only the bottom ply is in contact with the feed dog's teeth, and the top ply is expected to slide below the presser foot with negligible friction (along with the bottom ply), there is no positive binding force between the two plies.

Figure - 1 Drop Feed Mechanism

The drop-feed system is subjected to extreme interply slippage (for slippery fabric or fabrics with very low frictional value) or marginal interply slippage (for very high frictional surface value), depending on the surface characteristics of the fabric.

When the needle is up and the stitch tightening takes place, the feed dog is also up and the fabric is assisted from the top by the presser foot and from the bottom by the feed dog; thus, there is no chance that the fabric is strengthened by the sewing thread tension, and the drop feed is widely considered to be the most ideal for sewing lightweight fabrics.

When two or more fabric thicknesses are sewn, irrespective of whether they are separate fabrics or folded sections of the same fabrics, the problem arises that the friction between the bottom ply and the feed dog is greater than that between the plies that intervene. The lower ply's tendency to move forward satisfactorily with feed dog and the upper ply retarded by the presser foot is known as interply shift, differential feeding pucker or just feeding pucker.

Needle Feed (Compound Feed) Sewing Machines

Combined simultaneous feed action of a needle feed and drop oscillation feed is a compound feed and is useful for sewing with low inter-ply friction coefficient. The needle and feed dog together feed the fabric in a compound feeding system, while the needle is down and inside the fabric (Figure-2). In a pendulum movement the needle moves in the direction of the stitch (the tip of the needle actually moves in an arc). As the fabric is being moved from the bottom by the feed dog while the needle is inside the fabric, interply slippage is controlled. As the arc duration of the needle movement is minimal (0.083 inches for 12 SPI), and the thickness of the fabric layer being sewn is also negligible, the resulting inter-ply slippage is negligible to be observed in sewn content.

Figure - 2 Needle Feed Mechanism

Nevertheless, when the needle is up and the stitch tightening takes place, the feed dog is down and the feed dog does not support the fabric from the bottom and, thus, there is a risk that the fabric will bulge/buckled by the sewing thread tension in the event that there is not enough rigidity in the fabric plies. In thick material sewing (car seat cover, shoes, upholstery, luggage, etc.) compound feed can control inter-ply slippage, but can not be used for lightweight fabrics.

Compound feed is used in the multiple-ply sewing of dense fabrics to prevent inter-ply slippage, navigating the corner of acute-angle-shaped components while top-stitching at the edges. Double-needle lockstitch devices usually have a needle feed device.

Unison Feed Sewing Machines

All of the feed dog, needle and presser foot travel together to feed the fabric while the needle has entered the fabric plies inside. The presser foot is divided into two parts; one part has teeth underneath and moves in the direction of feed while the other part moves only up and down and holds the fabric between feed strokes during the formation of the stitch (Figure-3). Unison feed is used to sew thick materials such as tarpaulin fabric, polyvinyl chloride (PVC), and leather into multiple plies. It helps to do consistent sewing of all types of thick materials over cross-over seams without pitch errors (no-stitch gathering or stitch elongation).

Figure - 3 Unison Feed Mechanism

Differential Drop Feed Sewing Machine

Here two feed dogs are positioned in a differential position in a sequence in which the feed dog lengths match one another in a straight line, one behind the needle and the other before the needle (Figure-4). The rear feed dog (away from the operator) is called the primary feed dog, while the front feed dog is called the differential feed dog (closer to the operator). When the differential feed dog takes slower or quicker strokes than the main feed dog, a linear compression force is applied to the cloth, and vice versa. The volume of feed may be changed separately by two feed dogs. Nearly all sewing machines with an overlock and/or cover stitch have a differential feed system. Differential feed ensures forced compression of the fabric in all areas where fabric is susceptible to stretching during stitching (diagonal and curved edges), which counterbalances the stretch and maintains proper seam form and length.

Figure - 4 Differential Feed Mechanism

Variable Top and Bottom Feed Sewing Machines

One feeding foot on top and one feeding dog underneath the throat plate feed together with the cloth plies. Feeding foot bottom has a dented base. Feeding takes place whereas the needle is outside the plies of the thread. Here the top feed and the bottom feed quantities can be changed individually to create interply slackness or tension in the sewn cloth. The presser foot is in two sections, one holding the fabric in position while the stitch is being formed and the other having teeth on the bottom side and moving or walking in such a way that the top ply is positively taken along while the needle is out of the material (Figure-5).Positive regulation of the top ply allows for modifications so that either the fabric plies are fed exactly together or the top ply is deposited in the bottom ply, if necessary.

Figure - 5 Variable Top and Bottom Sewing Mechanism

The feeding foot works before the needle to create a gathering in the top ply, for instance giving fullness when sleeve setting in a blazer's armhole, and works behind the needle to create smooth seams, such as centering the blazer back edge. The feed difference which can be created in the best way between top and bottom ply creates completeness but can not create visible gathers in one ply.

Variable Top and Bottom Differential Feed Sewing Machines

One feeding foot at the top and two feeding dogs (like differential feed) underneath the throat plate feed together with the plies of fabric. The bottom of the feeding foot has underneath teeth. Feeding happens while the needle is outside tissue plies (Figure-6). This mechanism allows to sew two plies while the bottom ply remains flat with the top ply gathering. Here the gap in the feed that can be produced at best between the top and the bottom plies produces clear gathers in one ply. This feed system is available with an overcovering machine; it is possible to join long panels in skirts with a smooth flat seam without interply slippage, as well as join a waistline in a dress with a bottom ply collected and sewn with a smaller bodice block.

Figure - 6 Variable Top and Bottom Differential Feed Mechanism

X Feed Sewing Machines

Typical Corporate X-feed is characterized by needle feed and alternating drop feed. The feed dog is divided into two independent feed dogs; the central one has a needle hole and acts as a needle feed, and the side one acts as a drop feed. The needle enters the material during the first half of the stitch length and also through the central feed dog's hole (which is in' up') and transports the fabric just like the compound feed mechanism; the side-feed dog is below the level of the throat plate (Figure 7 (a) and (b)).

Figure - 7 X Feed Mechanism

(a) Central feed dog (gold color) is up and transporting the fabric

while the needle is down. (b) The side feed dog (sky blue color) is up and transporting the material

while the needle is up.

The central feed dog descends when the needle leaves the material and goes up, and the side-feed dog comes up and transports the material in the direction of sewing just like the drop-feed mechanism. As the side-feed dog carries the material in the direction of sewing, the thread take-up lever pulls the thread, an effect that stretches the stitch out like on a puller. By contrast with the sporadic feeding of drop feeding, the material transfer is constant and steady due to the alternating activity of both feed dogs.

Computerized Machine

Computerized sewing machines have tiny screens on the panel for smoother operation. Many different motors are operated using a computer-precisely moving the needle bar, the tensioning disks, the feed dog and other parts of the sewing machine. All those fine controls are operated by the machine, so hundreds of different stitches can be made. With the motor, the computer controls the correct speed in a particular stitch pattern to move the needle bar up and down from side to side.

Needle and Types of Needle