The tumbler gear unit consists of three gears, having the same number of teeth and it connects the spindle gear to the fixed gear. Tumbler gear unit is also called the reversing gear unit as it is used to change the direction of feed of the tool for the same direction of rotation of the spindle. Tumbler gear unit can be engaged and disengaged with the fixed stud gear by the operation of the hand lever provided in the unit.
Crank and slotted link mechanism is the quick return motion mechanism is commonly used in shapers.