Rack and pinion
Converting rotary motion to linear motion.
A rack and pinion mechanism is used to transform rotary motion into linear motion and visa versa. A round spur gear, the pinion, meshes with a spur gear which has teeth set in a straight line, the rack. The rack and pinion can transform rotary motion into linear motion and visa versa in three ways:
a. Rotation of the pinion about a fixed center causes the rack to move in a straight line.
b. Movement of the rack in a straight line causes the pinion to rotate about a fixed center;
c. If the rack is fixed and the pinion rotates, then the pinion's center moves in a straight line taking the pinion with it.
rack and pinion
The spur gear is the last gear we will look at and the most important as far as we are concerned. We will be looking at the gear terms and how to draw the gear teeth using Unwins construction. Firstly, we will discuss the spur gear itself.
A spur gear is one of the most important ways of transmitting a positive motion between two shafts lying parallel to each other. A gear of this class may be likened to a cylindrical blank which has a series of equally spaced grooves around its perimeter so that the projections on one blank may mesh in the grooves of the second. As the design should be such that the teeth in the respective gears are always in mesh the revolutions made by each is definite, regular and in the inverse ratio to the numbers of teeth in the respective gears. This ability of a pair of well made spur gears to give a smooth, regular, and positive drive is of the greatest importance in many engineering designs. An example of two spur gears in mesh are shown below.
Now that we have discussed the spur gear, we will look at the terms associated with spur gears