LO 5-4 Define concentricity and explain methods to measure it

LO 5-04: Define concentricity and explain methods to measure it.

Measuring Concentricity

Measuring concentricity of an object involves determining how closely a circular object is centered around its axis. In other words, measurement of an object’s concentricity determines how circular it is or whether it has runout and how much runout is present. An example of a concentricity measurement would be of a rotating shaft (such as a crank- or camshaft) bearing journal surface FIGURE 28. The shaft is first supported at each end on narrow blocks called vee blocks , where it is slowly turned. Next, a dial-type indicator with a roller-type tip is placed against the journal surface around the shaft’s centerline. A movable plunger on the dial indicator transmits any lateral movement of the shaft to a rotating gauge, enabling measurement of how much movement takes place. When there is no difference between the axis of the shaft and its outer surface, the shaft is said to be concentric. Runout of the shaft, which is where the pointer of the dial indicator moves in or out while rolling over the shaft surface, means the shaft is not concentric. Camshaft lobe lift is measured with continuous-type dial indicators and is expected to be nonconcentric.

FIGURE 05-28: Measuring camshaft lobe lift. The lobe will be nonconcentric with the centerline axis of the shaft.

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