SINGLE NEEDLE LOCKSTITCH MACHINE PDF

Structure[ edit ] The lockstitch uses two threads , an upper and a lower. Lockstitch is so named because the two threads, upper and lower, "lock" entwine together in the hole in the fabric which they pass through. The upper thread runs from a spool kept on a spindle on top of or next to the machine, through a tension mechanism, through the take-up arm, and finally through the hole in the needle. Meanwhile the lower thread is wound onto a bobbin , which is inserted into a case in the lower section of the machine below the material. To make one stitch, the machine lowers the threaded needle through the cloth into the bobbin area, where a rotating hook or other hooking mechanism catches the upper thread at the point just after it goes through the needle. The hook mechanism carries the upper thread entirely around the bobbin case, so that it has made one wrap of the bobbin thread.

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Figure-1 shows the single needle lock stitch machine. The one side of the needle has the eye and a sharp tip while the other side is attached to a needle bar that moves up and down to form a stitch. The arm also secures a presser foot which presses the fabric while sewing.

The needle penetrates into the fabric from the top, to bring the needle thread through the fabric to the bottom to form a stitch. Figure Single needle lockstitch machine The needle thread in a spool is threaded through the thread guides, tensioning mechanism and into the sewing needle eye.

The bottom thread bobbin thread is wound onto the small package called a bobbin before sewing and is secured inside a bobbin case. For stitch formation, the needle brings the needle thread loop to the bottom of the fabric where a small hook on the bobbin case catches it.

As the bobbin hook rotates, it takes the needle thread around the bobbin to produce a stitch and then the take-up lever takes back the extra loop of top thread to tighten the stitch. As the needle is out of action of fabric, the feed dog comes above the throat plate, and pushes or moves the fabric up against the presser foot for next stitch.

Working principle of Single needle lockstitch sewing machine: 1. The single needle lockstitch sewing machine is getting drive from the electric motor which is mounted in sewing table. The main parts of the sewing machine are flywheel, eccentric or cam, needle bar, bobbin holder, feed dog and presser foot.

The flywheel is driven by motor belt and it drives the sewing machine main shaft. Figure Needle bar and Pressure foot mechanism 3. The every rotation of the main shaft moves the needle a full cycle of up and down movements.

The main shaft is further connected with a bevel gear and two connecting rods to transfer the motion to the bottom of the machine. The bevel gear rod is used to transfer the motion to the bottom centre shaft, which is the main shaft for connecting the bobbin shuttle mechanism. This connection helps the bobbin shuttle to move. The bevel gear mechanism helps to transfer the motion without any energy loss shown in Figure Figure Motion transfer from main shaft to bottom shaft 5.

Every one revolution of the main shaft is connected to the every revolution of shuttle hook to make one unit stitch. The other two connecting rods from main shaft are used to connect with the feed dog, which has a synchronized movement with needle and bobbin shuttle mechanism.

The feed dog has to perform four stop motions for every cycle of stitch formation. The feed dog gets drive from main shaft in two ways, one is rotation — to deliver the unit length of the fabric for sewing and another motion is the up and down movements above the throat plate of the sewing machine. In Figure-4, the rod 1 helps the feed dog to move up and down for the selected distance based on the settings kept.

The rod 2 is used to move the feed dog to and fro as required. Figure Bottom main shaft and mechanism. When ever, the stitch regulator is adjusted, the feed dog delivers the required amount of fabric needed by adjusting the feed bracket as shown in Figure The revolution per minute of the feed dog is same as the needle stroke. Figure Feed dog movement from bottom shaft connection All these motions work together from the single motion of main shaft and help the machine to form the stitch.

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Lockstitch

Top 10 amazing movie makeup transformations A lockstitch sewing machine binds cloth together with two spools of thread and a needle with the eye at its base. Distinct from a chain stitch machine, a lockstitch sewing machine makes strong, straight seams. It was the first kind of commercial sewing machine to secure a patent, enter manufacturing, and place automatic sewing in the hands of millions of households. Most homes have a lockstitch sewing machine because their basic stitch can be used for a wide variety of applications. The machine works by interlocking two threads from two bobbins that cannot unravel easily, unlike a chain stitch. The length of the stitch, as well as tautness, can be controlled by dial.

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