Dial Indicator

Dial Indicator

Dial indicators which are also called dial gauges, or dial test indicators (D.T.I.), are direct reading precision measuring instruments.

They are designed mainly to measure movement rather than thicknesses, although exceptions exist - such as a dial indicator used as part of a bore gauge or dial type vernier caliper

In mechanics, the dial indicator is typically used to measure end play of a shaft, taper and out of round of a bore, backlash of a gearset, runout of a brake disc, etc.

Both S.A.E. and metric dial indicators are available. Use the one which matches the specifications of the object to be measured. If a specification, for instance, is in thousandths of an inch, use an S.A.E. dial gauge. If the specification is in hundredths of a millimeter, use a metric tool.

The illustration below shows a typical S.A.E. dial indicator and the names of some of its parts.







Use of dial indicators
When using a dial indicator, observe the following basic rules:

Don't drop it

Select the correct trace pin tip for the job
^ round tip for a flat object
^ flat tip for a round object
^ roller tip for a rotating object ( i.e., brake rotor)

Preload at least 2 mm or .10"

Note that the indicator needle moves clockwise when the trace pin is pushed into the stem of the dial gauge and vice versa

Make sure that the dial gauge holder or setup is firmly clamped to prevent lost or false motion

S.A.E. Dial Indicator
Most S.A.E. dial gauges are accurate to .001 inch. For more accuracy, a .0005 inch (one half thousandth of one inch) unit is available. The measuring range is usually ether .5 inch or 1.0 inch.

The illustration below shows a typical .001 inch indicator with rev counter. In this example, the dial gauge was preloaded to .10" and reads .015" from the zero point on the dial.







Metric Dial Indicator
The metric indicator is similar in appearance and operation to its S.A.E. Counterpart. Most are graduated to .01 mm increments which roughly correspond to a .0005" S.A.E. Instrument for accuracy.

Note in the example below that the tool was preloaded to 2.0 mm and has traveled .22 mm from the zero point on the dial.