Sewing Machines

234. Different Types of Sewing Machines. There are two types of sewing machines in use—the chain-stitch and the lock-stitch. Sewing machines are made to run by hand, foot or mechanical motor power. This makes no difference in design or care of the stitching part of the machine. Motor and foot power run the machine faster than hand power.

The treadle of the foot-power machines swings on pivots. These should be kept oiled and clean from lint and thread. The large and the small wheels for the belt should be oiled at the axle.

235. Lock-Stitch Sewing Machine. A lock-stitch sewing machine (Figs. 132 and 133) consists of shafts and wheels which move the needle, feed plate and bobbin. The top thread is guided from spool to needle thru a tension so that only the needed amount passes forward each time the needle is raised after the thread has caught in the cloth.

When there is a difference in the size of the thread used on the machine, the tension must be adjusted to fit the thread, unless the tension is automatic. If the tension is not properly adjusted or the machine threaded properly, the thread will either break, tangle at the needle point, or draw the top thread tighter than the bottom one (Fig. 134).

A longer stitch is needed for coarse thread than for fine thread.

236. Feed Plate. A device below the needle called the feed plate (No. 34, Fig. 132) shoves the cloth faster or slower under the needle, according to its adjustment, thus making a longer or shorter stitch. This device is a rough plate which moves backward each time the needle is raised, and forward again when the needle comes down. While moving backward, the rough surface moves the cloth, but it drops slightly below the level of the table as it moves back into place, so does not affect the cloth. For short stitches, it moves with a short stroke, and for long stitches, with a long stroke. If the feed plate becomes gummed with lint and oil, the machine will not make even stitches and may fail to move the cloth. Sometimes it will fail to stitch. Improper threading may break the needle thread. Too tight a tension may break it. Too coarse thread for the size of the needle may break the needle. A bent, blunt pointed or incorrectly set needle may break.

237. Bobbins. There are two styles of bobbins used on lock-stitch sewing machines—the shuttle bobbin (Fig. 135) and the round bobbin (Fig. 136), depending on the particular type of machine used.

238. Shuttle Bobbins. In shuttle bobbins, there is a long iron spool on which the thread is wound. This is put into the bobbin with the twist in the direction indicated in the book of directions for the machine being used, and the thread is drawn thru the slits and holes in the bobbin which govern the tension of the lower thread (see Fig. 135).

Put the shuttle into place and draw the thread up over the feed plate (Fig. 137). The machine moves the shuttle backward and forward, and as this happens, the needle is timed to drop down, leaving a loop of thread in such a position that the bobbin passes thru it. In rising, the needle pulls the loop up tight, and as it has passed thru the cloth, this cloth comes in between the thread from the bobbin on the under side and the thread from the spool on the upper side, which have been interlocked by the bobbin having passed thru the loop of thread from the spool as the needle carried it down below the cloth. This is called the lock-stitch (Fig. 134). The spool bobbins also pass thru the loop left after the needle has passed downward.

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239. Chain-Stitch Machine. In the chain-stitch machine (Fig. 138), the shaft turns a device which draws a loop of thread thru each foregoing loop, thus making a stitch similar to crocheting, but having the cloth interlocked with the stitch. The needle carries the thread and makes it tight or loose as needed. The feed plate carries the cloth under the needle.

There is a tension to govern the thread. As a single thread is used in making this stitch, no bobbin is used. The tension must be tight enough to draw the loop of thread about the cloth, or else the thread will tangle.

240. Cautions for All Machines. Machines should be kept well oiled, and they must be kept free from thread and lint, for these are the things which give trouble in machines. Never try to draw the cloth under the needle any faster than it is pushed along by the feed plate under the presser foot. Pulling on the cloth bends the needle from the exact path which it should follow.

Move the treadle with a smooth, even motion—a jerky motion wears out operator and machine. Use only the best sewing-machine oil. Poor oil gums the parts of the machine. Clean the machine every day it is in use. Take care to set the needle in its proper position, and fasten it firmly in place.

241. General Instructions. Thread the machine exactly according to instructions. If not properly threaded, it will fail to stitch—the thread will tangle. If the bobbin is not properly threaded, it will not have the proper tension, and the machine cannot sew as it should. The bobbin thread will break if it is not properly threaded thru the bobbin case. It will also break if the bobbin tension is too tight (No. 14, Fig. 138).

Always regulate the stitch and the size of needle for each size and kind of thread used. A table for this usually comes with each machine, or is often stamped on the machine. Select the thread suitable to the material. The number of a needle is marked on the shank. Needles made for one kind of machine will not always work on another.

An automatic tension should not be changed or meddled with. Some tensions must be adjusted to the thread. Follow directions coming with the machine for adjusting tensions. Remove any thread which has become entangled in the mechanism of the machine.

Never use a bent needle. A bent needle drops stitches on a chain-stitch machine. Soaping the needle helps it to go thru goods difficult to penetrate.

When a machine runs hard, it needs oil or has become gummed up with poor oil. When gummed, clean with kerosene oil. Thread or ravelings wound about the axles of the wheels also makes the machine run hard. Learn to use the attachments of your machine—take care that they do not become bent.

The lock-stitch does not rip easily.

The ends of the thread of chain stitches should be carefully fastened. If started from the end where the seam was completed, the loop stitch may be easily unraveled and thus save time when mistakes are made in sewing or when garments are being made over.