A Curved and Linear Shuttle Track

Early Lockstitch machines had boat shaped shuttles held loosely in a cradle on the end of an oscillating lever. All the mechanisms in the machine had to remain in sync and toothed gears were not easy to machine so cams and levers were the best answer. This meant that the shuttle had a curve and was itself difficult to produce.
Later, toothed gears led to the production of a linear shuttle race driven by a crank. The acceleration and forces at each end of the stroke were less and the rotating part acted as a flywheel so greater speeds were possible. The shape of the shuttle was also simpler.
Later, rotary shuttle movements were to become the norm. These were faster and much quieter.	However some manufacturers such as Jones and Harris were still producing linear movements up to the mid 1900s.