Cast iron is commonly used for machinery housings or base due to its damping characteristics. It is also known for holding its shape when it is subjected to contraction and expansion due to temperature fluctuations. Hence lathe bed is usually made up of cast iron.

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. Tumbler gears in lathe are used to give desired direction of movement to the lathe carriage.