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High-Friction Applications
No different than the parts in a motor, some applications are prone to much more friction than others. For example, if the probe on a dial indicator is measuring an osculating movement like the opening and closing of a valve tappet, it simply compresses and releases the indicator; there is little friction exerted on the probe tip. Such applications are less prone to tip wear due to friction. If the same indicator is used to measure the rotation of a cam shaft, every millimeter of movement drags nearly perpendicular across the tip. On a microscopic scale, it is like sandpaper removing molecules and wearing the tip down. Tool steel or hardened steel may not be adequate to stand up to this environment.
Indicator Tip Shape
Just like pencil lead, a fine tip will wear down faster than a relatively flat tip. Where hardened tool steel may work in a flat-ended cylinder shape -- because it's not nearly as hard as carbide -- it will wear much faster. A combination of an acute "V" or pointed tip shape and a high friction application is the most demanding and prone to friction wear.
Knowing Your Tolerances and Wear
It's important that you know your tolerances. That means you know the range of inaccuracy that is acceptable. Even the finest machinery is prone to wear. The objective is to make the accuracy of the measuring device well within the required tolerances. For the most demanding applications, where indicator tips wear quickly, it means using the most durable tips and knowing how often they need to be replaced or how often the measuring device needs to be re-calibrated.
Carbide and Carbide Alloys and Steel
Steel is an alloy derived from iron, then heat treated for hardness. In the case of hardened tool steel, the mix of alloy is chosen for attributes such as hardness and corrosion resistances, such as chromium. Several ultra-hard elements such as carbide, tungsten and cobalt can be added. When choosing a carbide tip, it's important for you to understand whether or not you're getting a pure carbide tip -- which usually means a tungsten-carbide alloy -- or whether there is a light carbide surfacing. The difference goes back to knowing your tolerances. If you wear through carbide to the underlying hardened tools steel, you need to replace the tip. If you wear the carbide tip, you can re-calibrate the measuring device and expect continued low-wear performance.