The central bobbin hook, or CB hook, was invented in 1887 and first used in its proven form by Singer in 1920. Unlike older models with a swing shuttle, the bobbin case, including the lower thread spool, is located in the center of the hook. In contrast to the circulating hook, the central bobbin hook swings back and forth, picking up the upper thread, guiding it around the bobbin case with the lower thread spool, and then swinging back. The central bobbin hook sews at a speed of approx. 2000 stitches per minute. A major advantage is the clean stitch pattern, as the thread is not twisted. The central bobbin hook also works with mostly standard bobbins, and spare parts are still available on the market. In addition, the CB hook is now installed in most inexpensive household sewing machines, as the system is inexpensive to produce. The CB hook can be easily removed, cleaned and reassembled for cleaning and maintenance. As it is very robust, the mechanism is relatively low-maintenance, but does require a little oil from time to time. Signs of wear, an unclean stitch pattern or so-called “thread jamming” are usually accompanied by increased noise from the CB hook and indicate that maintenance or repair is required.
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