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A bobbin is a spindle or cylinder, with or without flanges, on which wire, yarn, thread or film is wound. Bobbins are typically found in sewing machines, cameras, and within electronic equipment. In non-electrical applications the bobbin is used for tidy storage without tangles.
The lockstitch sewing machine, invented and developed in the 18th and 19th centuries, forms a stitch with two threads: one passed through a needle and another from a bobbin. Each thread stays on the same side of the material being sewn, interlacing with the other thread at each needle hole thanks to the machine's movement. Tension of the bobbin thread is maintained with a bobbin case, a metal enclosure with a leaf spring which keeps the thread taut. The bobbin case has to be free-floating (not attached to an axle) in order to allow the top thread to pass around the bobbin completely and hook the bobbin thread.
Bobbins vary in shape and size, depending on the style of bobbin driver in the machine for which they are intended to be used. Long, narrow bobbins are used in early transverse shuttle and vibrating shuttle machines. These earlier movements were rendered obsolete by the invention of the rotary hook and the shuttle hook, which run faster and quieter with less air resistance. These shorter, wider bobbins are familiar to modern sewers, as the rotary/shuttle hook remains in use on modern machines essentially unchanged.
Bobbin lace requires the winding of yarn onto a temporary storage spindle made of wood (or, in earlier times, bone) often turned on a lathe. Exotic woods are extremely popular with contemporary lacemakers. Many lace designs require dozens of bobbins at any one time.
Both traditional and contemporary bobbins may be decorated with designs, inscriptions, or pewter or wire inlays. Often, bobbins are 'spangled' to provide additional weight to keep the thread in tension. A hole is drilled near the base to enable glass beads and other ornaments to be attached by a loop of wire. These spangles provide a means of self-expression in the decoration of a tool of the craft. Antique and unique bobbins, sometimes spangled, are highly sought-after by antiques collectors.
Electrical transformers, inductors and relay coils use bobbins as permanent containers for the wire to retain shape and rigidity, and to ease assembly of the windings into or onto the magnetic core. The bobbin may be made of thermoplastic or thermosetting (for example, phenolic) materials. This plastic often has to have a TÜV, UL or other regulatory agency flammability rating for safety reasons.
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