What can cause false readings on a dial indicator?

False readings on a dial indicator can arise from various factors, and bar sag from attached weights is particularly significant. When a dial indicator is used, especially in a setup where weights are attached to the measuring arm or bar, any sagging due to excessive weight can cause the indicator to record measurements that do not accurately reflect the true alignment or position of the surfaces being measured. This sag can create a situation where the measuring surface is not perpendicular or aligned properly, leading to measurements that are off, which can misinform the technician performing the alignment work.

Other factors such as excessive lubrication, cabling issues, and incorrect calibration can also impact readings, but they operate under different principles. Excessive lubrication may create a slippery surface that could distort the readings, cabling issues can affect the response of the indicator, and incorrect calibration means that the tool may not measure accurately from the start. However, bar sag is a unique issue that directly alters the positioning of the measuring element, making it a crucial consideration during alignment tasks.