A dial indicator is a measuring device, which are one of the most primary measuring tools utilized in the precision manufacturing process. For instance, in the engine building, they are typically used to measure deck clearances, crankshaft thrust and straightness. Lifter travel and other measurements that involve the distance between two surfaces or small amounts of component travel are also common in the dial indicator inventory.
This device aims at comparing measurements between two objects so inspection technician can check the conformity of one of the objects. The second one is normally the reference for the first one. The dial indicator can be used in many objects while for the final checking shall also be checked by other devices because for precision manufacturing there are many key issues that need to be further inspected by ultra-precision devices such as the CMM system.
Compared with dial indicator, CMM is much accurate but cannot be conducted by manual operators all over the whole process since the working mechanism is different form dial indicator. A CMM machine is a coordinate measuring machine, which is a device that measures the geometry of physical items by sensing discrete points on the surface of the targeted item with a probe. There are many types of probes which are adopted in CMMs, including mechanical, optical, laser, and even white light. There can be many variants.
Depending on the machine models, the probe position may be manually controlled by an onsite operator or it may also be computer controlled based on the programs. In practice, CMMs typically specify a probe's position in terms of the displacement from a reference position in a three-dimensional Cartesian coordinate system, which are with XYZ axes. Moreover, in order to moving the probe along the X, Y, and Z axes, many machines also allow the probe angle to be managed to allow measurement of surfaces that would otherwise be unreachable. In the machine tool industry, the CMM equipment is widely used to do precision measurement for the work piece as well as other objects, so to achieve the intended accurate processing within the intended standard.
Conventional indicators of measuring provide a dial display similar to a clock face with clock hands, which point to the graduations in a circular scale on the dial. The dial represents the distance of the probe tip from a zero setting as the basis. The inner works of a mechanical dial indicator are close to the precision clockworks of a mechanical watch, which employs a rack and pinion gear to read the probe position. The side of the indicator probe shaft is cut with teeth, providing the rack gear. So, when the probe moves, the rack gear would drive a pinion gear to rotate, and spin the indicator. Springs are preloaded for the gear mechanism to minimize the backlash error in the reading so that the backlash would not cause further misread. There are various names for dial indicators, such as probe indicator, dial gauge, pointer, clock, test indicator, dial test indicator, etc.
Although there are digital or electronic readouts of dial indicators, most of them are still designed in analog and the dial size referred to typically by the AGD, American Gauge Design Specification. There are primarily six phases to be counted by a dial indicator. They are accuracy, range of travel, number of dial revolutions, dial style, graduation style, and revolution counters. The graduation style is typically positive numbers or negative numbers, and the revolution counters indicate the number of revolutions of the principal needles.
The deployment of dial indicator in the grinding process is very common. Machine tools are the most fundamental capital goods for manufacturers and they play the critical roles that determine the final output of the end products. So both dial indicators and CMM are used in the process often. The quality of the machine tool, as this reason, is the key point of the quality of the manufacturers’ final end products. The inventory of machine tools varies from time to time. Now after the invention of the machining centers and the CNC programmed controlling system, the standards of machining become more and more rigid compared with the standards before.
Besides the CNC machining centers, there are also other CNC models, such as CNC turning centers, CNC milling machines, CNC tapping and milling centers, CNC drilling and milling centers, etc. Those machines, though not as versatile as machining centers, are also very strong in machining all kinds of work pieces with complicated methodologies so that the use of the dial indicators for the preliminary is possible and can help for the first step basic inspections.
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