Rack & Pinion
Rack and Pinion is a form of a linear actuator that includes a pair of gears that convert circular motion into linear motion. The rotating gear is called the pinion and the linear gear is called the rack. The pinion engages its teeth on the rack and moves in a rotational manner. This causes the rack to move and translates the rotational movement of the pinion into the linear movement of the rack.
The rack and pinion drive systems are quite rigid and stiff. They do not require much maintenance, have high resistance to dust, can be extremely fast and their chips are excellent for medium to large CNC tables. Although they do not work equivalently on lighter tables as they can cause a backlash, the degree of it is dependent on the quality of the table.
The application of this system is used in the 5000 Series CNC Router and 6000 Series CNC Waterjet. In these machines, it is the helical rack that is used, not the straight rack. Helical rack and pinions run very quietly, especially at high speeds. Due to the angular cut in the helical rack and pinion setup, there are thrust loads on the gear shaft. This action requires thrust bearings to absorb the load and maintain gear alignment. Refer to previous blog post, Rack and Pinion Backlash for further detail.
A belt drive is transferring rotary motion between two shafts. A belt is a loop of elastic material that is used to connect two or more revolving shafts mechanically. Belts transmit power efficiently through tracking relative movement. They are looped over pulleys and move in a two pulley system. The belt can drive the pulleys in the same direction or they can be crossed to create movement in opposite directions.
Belt drive pulleys do not require periodic replacement. They are designed to be easy and flexible equipment since tolerances are not important. The driven shaft speed is conveniently changed by altering pulley sizes. They also do not require lubrication and makes maintenance relatively simple. To top it off, they are very quiet while operating.