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A dial indicator, sometimes also called a clock indicator, a dial gauge, a probe indicator, or a comparator, is a measuring instrument used in many industries where precision is necessary, such as manufacturing, designing, and scientific businesses. The indicator is a spring-loaded spindle, or plunger, connected to a clock-faced dial. As the spindle moves in and out of the indicator, a needle on the dial shows the measurement of the distance, which in turn reveals the depth of the depression. Using this instrument is normally pretty simple. An operator lifts the indicator's spindle with a lever, slides the item he or she wants to measure under it, and lowers the spindle. If the part varies from the reference, the indicator’s dial registers the deviation. On some indicators with a larger range, a smaller face within the larger tracks each revolution.
These sorts of tools are used in a wide variety of industries. In manufacturing, professionals typically use them during machine set-up to center stock and determine the accuracy of lathe or mill alignment. Production machinists also use indicators to monitor the depth of holes, keyways, and ledges. Many quality control technicians use them to check variation in machined part tolerance.
Indicators are also important in laboratories for recording and measuring small movements, either of mechanisms or particles. In automotive repair shops, they help mechanics fit new discs in disc brakes, where the tolerance can be as low as 0.0019" (0.05 mm). In home woodworking situations, crafters can use them to set up their lathes and saws, and monitor drilled hole depths. In essence, this tool can be very helpful any time a person needs a precise reading or calibration, no matter the setting.
The sizing specifications for this tool can vary greatly. Generally, indicators have a range of 0.250 inches to 2 inches (6.35 mm to 50.8 mm) and give measurements in increments of 0.001 inches (0.0254 mm). Some specialty instruments measure in the range of around 0.015 inches (about 0.25 mm) while others go up to 12.0 inches (about 30.5 cm). Graduation markings on the dial can vary from 0.00005 inches to 0.001 inches (about 0.001 mm to 0.01 mm) in typical indicators.
Most modern models have digital readouts rather than the more traditional clock face readout. Among other things, the digital technology makes it easy to switch between imperial and metric measurements. Some have the capability to transfer the measurement data to a computer as well, or to store data wirelessly in the cloud or some other remote database.
In most cases these tools are not accurate unless mounted to a base. The typical indicator holder is a magnetic-based stand that has an arm, or arms, to hold the measuring apparatus in a variety of positions. Sometimes engineers design unique mounts to support the instruments for special jobs.
Having the indicator secured to a rigid base or stand helps the user in two ways. First, the instrument is more accurate without user interference. Another advantage of a base is that it gives the spindle a master part or reference point against which to measure the item. Usually a machinist will establish a reference point by rotating the large hand of the dial to zero before they measure a depth.
There are a couple of things customers should consider when buying these tools, but a lot of the decision will be driven by the expected usage. Since coolants, oil, water, and other contaminants can ruin the instrument, most machinists buy waterproof and dust-proof dial indicators. Better indicators have jeweled movements, which typically offer a better lifespan though they can cost more at the outset. A buyer should also usually think about whether gauge accessories, such as stands, extra contact points, and replacement parts, are available and, if so, how easy they are to obtain.
A similar tool known as a dial test indicator is often similar and may sometimes be used in place of the more standard dial indicator, but it’s usually more precise and has more nuanced uses as well. Typically, test indicators have a smaller measuring range and are more precise. Instead of having a spindle, they have a levered arm with a balled tip that moves up and down. In many situations, a dial test indicator can do measurements that a dial indicator cannot do. Most serious machinists have and use both instruments.
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