As stated earlier, the operations of a mechanical sewing machine begin with a motor. This provides the speed and torque required to rotate and run the mechanical parts of the machine, including the needle’s up and down movements, feed dog movements and shutter rotation.
To give you some flexibility, most motors are controlled using a foot pedal, which basically acts like a car’s accelerator, allowing you to speed up or slow down the machine’s stitching speed by adjusting the foot pressure you apply to the pedal.
Threading is essential to any type of sewing machine. In fact, no stitching can be made if the machine is not threaded.
A mechanical sewing machine works by pulling in two threads, one coming from the spool above and the other from the bobbin, then loops one around the other to create a stitch.
This, therefore, means that the bobbin must be filled with thread and inserted into its slot beforehand. The upper part of the machine also needs to be threaded, with the yarn being passed through all the guides down to the needle eye.
The actual stitch creation process involves an important but hidden part of the machine called the shuttle.
What happens is that as the needle pierces the fabric, it brings down with it the top thread and passes it through the punched hole. In this lowered position, the shuttle underneath the needle plate grabs this thread via its hook, then rotates so as to loop it around the bobbin thread. This interlocks the two threads, thereby creating what is commonly referred to as a loop stitch.
As this loop is being created, the needle moves upwards and tightens the upper thread, thereby tightening the stitch. However, the thread tension and stitch tightness are also determined by the machine’s tensioning settings.
This whole stitching process is synchronized and everything happens so fast that the eye cannot see, especially when sewing at high speeds.
The other important activity that is part of the synchronized stitching process is the fabric pulling or feeding. This pulling mechanism is made possible by two main parts, which are the feed dogs and presser feet.
Feed dogs are the grippy metallic teeth that raise and lower from the needle plate and they are interconnected to the motor’s movement together with all the other parts.
Basically, as soon as the upper and lower threads have been looped around the fabric and the needle has moved up, the feed dogs rise from the needle plate slot and move either from front to rear or rear to front, depending on whether you are front or reverse stitching. This movement then causes the fabric to move so that the next stitch is formed at a different spot.
Of course, some slipping can occur and this is where presser feet come in. Apart from providing a slot for the needle to pass through, a presser foot, as the name suggests, presses down on the fabric so that there can be enough friction for the feed dogs to grip the piece and move it.
That said, there are some instances in which you can opt out of the automatic fabric feeding in favor of freehand sewing, especially when creating customized decorations, but this is left for the highly skilled sewing pros.
Lastly, even though mechanical sewing machines are not as advanced and highly adjustable as electronic and computerized units, they still have some few customization options, which are primarily based on stitch width, stitch length, tensioning and needle position adjustments.
Stitch width adjustment basically creates a zigzag stitch, and the width of the zigzag ultimately depends on the machine’s settings. The machine creates this width by moving the needle’s position after every piercing from left to right and back.
As for the stitch length, this can be done on both the straight and zigzag stitch, and this setting basically adjusts the feed dog movements such that with a short length setting, they move the fabric in short steps, creating tightly knit stitches.
When set to a long length, the feed dogs move at a longer length, thereby moving the fabric through a longer distance after every stitch so that the next piercing is done much farther away from the last one.
The other important adjustment setting that is crucial to how a mechanical sewing machine works is the thread tensioning, and this is done to the upper thread using a dial located on the upper part of the machine.
Any adjustments made via this dial affects the tension at which the thread is fed through the needle, such that a high tension creates very tight stitches while a low tension creates loose stitches, which are ideal for certain embroidery projects such as monogramming.