Pitch angle in bevel gears is the angle between an element of a pitch cone and its axis. In external and internal bevel gears, the pitch angles are respectively less than and greater than 90 degrees.

roll out a sausage of plasticene on the glass. roll the gear along the plasticene to make a plasticene rack. measure the angle of the slope of the rack tooth face. this corresponds to the pressure angle./span>

Earlier gears with pressure angle 14.5 were commonly used because the cosine is larger for a smaller angle, providing more power transmission and less pressure on the bearing; however, teeth with smaller pressure angles are weaker. To run gears together properly their pressure angles must be matched.

This type of full depth tooth is most common, but other types with shorter or longer tooth depths are also used in some applications. Although the pressure angle is usually set to 20 degrees, can be 14.5 or 17.5 degrees in specific applications.

For straight bevels, the AGMA standard recommends pressure angles of 20º and, for 12 or 13 teeth, 25º. The angle is measured normal to the surface of the tooth. The smaller angles are sometimes necessary when very large gears stretch the capacity of the gear generator./span>

Involute splines are available in several different pressure angles: 30 degrees, 37.5 degrees, and 45 degrees. The 30-degree splines are by far the most common, so that is what will be considered here. Splines are made with either a fillet root or a flat root at the interface of the tooth flank and the root diameter./span>

In force closed cams, the pressure angle is important during the rise portion where cam is driving the follower, in return motion it is the spring force (or any other force used for forced closure) that lowers the follower. The pressure angle is a function of cam rotation angle.

BASE CIRCLE: The “base circle”, also known as the “heel”, is the lowest point of the camshaft lobe and is the place where the valve is in the closed position. The “base circle” is the point where all valve lash settings are made.

The first two numbers are the degrees of opening being 210 for the intake and 218 degrees for the exhaust given normally at .050 inch of lift. The next two numbers are the valve lift of intake and exhaust in thousands of an inch. The final number is the degrees of overlap.

A small base circle camshaft is one that is made with a smaller “core” to the camshaft. It has the same lift, duration etc.. but in a smaller “package” Basically a small base circle cam is used with some stroker motors if there are clearence issues between the cam and the rods/crank./span>

Base Circle is actually the distance accross the cam’s lobe. This is 90 degrees from the top of the cam’s lobe at the point of highest lift. You can easily measure this distance with a micrometer. Measure across the cam’s lobe (the lobe’s smallest distance)./span>

Cams are classified according to the direction of displacement of the follower with respect to the axis or oscillation of the cam. Cylindrical Cams These are often used in machine- tools and the cam imparts an oscillation or reciprocation to the follower in a plane parallel to the axis of the cam./span>

Cams are commonly used in engines to control valves (in which the valve is the follower), sewing machines, children’s toys and many other mechanical applications. The shapes of individual Cams are designed to produce specific types of motion.

The four types of motion are:

• linear.
• rotary.
• reciprocating.
• oscillating.