A plain sock knitting machine, also known as a sock knitting loom or sock knitting frame, is a specialized machine used for producing socks. It automates the process of knitting socks, making it faster and more efficient compared to hand knitting. 

Machine Setup: The sock knitting machine is set up by attaching the necessary components such as the cylinder, ribber, and yarn guides. The machine is also threaded with the desired yarn or thread.

Yarn Feeding: The yarn is fed into the machine through a yarn guide or feeder mechanism. The yarn is usually wound onto a bobbin or cone and placed on a yarn holder or creel. The machine guides the yarn through the necessary channels to start the knitting process.

Needle Selection: The machine has a series of needles arranged in a circular or semi-circular pattern on the cylinder. The needles are responsible for creating the stitches in the sock. Depending on the desired pattern or design, the machine selects and activates specific needles to knit or hold stitches.

Knitting Process: The machine starts rotating the cylinder, which causes the needles to move in a cyclical manner. As the yarn is fed and the needles move, stitches are formed. The machine follows a preprogrammed pattern or design to create the desired shape and structure of the sock. The length of the sock is determined by the number of rotations or the programmed pattern.

Heel and Toe Formation: Socks typically have reinforced heel and toe areas for durability. Some sock knitting machines have specialized mechanisms or attachments that automatically shape and reinforce these areas during the knitting process. This may involve selective needle activation or the use of additional needles or attachments.

Finishing: Once the knitting process is complete, the machine cuts the yarn and releases the sock from the knitting area. The sock may undergo additional processes such as trimming excess yarn, securing loose ends, and steam blocking to improve its final appearance and shape.

Removal and Packaging: The finished socks are removed from the machine, and any necessary finishing touches, such as sewing the toe seam, may be performed. The socks are then inspected for quality, sorted, and packaged for distribution or further processing.

It's worth noting that Plain Sock Knitting Machine can vary in complexity and features, depending on the Plain Sock Knitting Machine manufacturer and the specific model. Some machines may have additional capabilities such as pattern variations, different sizes, or the ability to knit multiple socks simultaneously.