A dial gauge or indicator consists of components such as bezel, indicating pointers, tool post and clamp, magnetic tool holder and sensor button. Dial indicators are available in many physical sizes and ranges. For most alignment applications the smaller sized indicators should be used to reduce indicator bar sag. Dial indicators that will be chosen should have a range of 0.100 inch and accuracy of 0.001inch.
Indicator readings and many other types of readings are expressed in several units. A reading of 1/1000” is equivalent to 0.001 inch and is commonly expressed as 1 mil.
The dial gauge has two scales (0-100) & (100-0), the (0-100) is outer scale while (100-0) is the inner scale. The outer scale is to be used when dial gauge needle moves clockwise and the inner scale is used when the dial gauge needle moves anticlockwise.
When the sensor of a dial gauge is pushed upwards towards the dial (calibrations), then the needle on dial gauge moves clockwise and when the sensor is moved downwards away from the dial then the needle moves in the anticlockwise direction. The reading when the needle moves in the clockwise direction is positive (+ve), while it can be referred to as negative (-ve) reading when the needle direction is in the anticlockwise direction. When being applied for alignment purpose the movement of the needle can be confusing especially when trying to understand whether it is positive reading or negative reading.
USING DIAL GAUGE FOR ALIGNMENT
All readings obtained at the primary level of alignment should be recorded as viewed from the stationary machine side to define right and left direction at the time of data entry.
Check the indicator for backlash error, press the sensor and then release and note down the dial gauge reading. Repeat this process two or three times. If in order, the readings should be the same for the several times’ repetition otherwise change the dial gauge because it will give a wrong reading in the process.
During alignment of machines, dial gauges usually come with a standard mounting system which makes it easy for it to be fixed at the position that will make it easy to align the machines. Generally, there are two ways the mounting can be carried out, which are:
Single gauge mounting and double gauge mounting, the initial is used when only one dial gauge will be used in the alignment process, while the latter can be used when more than one dial gauge is needed in the alignment process.
Sometimes depending on the equipment to be aligned some modification or extension is required in the mounting system to carry out the alignment. If the length of the tool mounting holder is more or any extension for mounting magnetic tool holder is there, then the possibility of sagging is more due to weight. Mounting of the dial gauge on the bracket should be performed carefully so that dial gauge sensor axis is perpendicular to the pipe axis to ensure accuracy. Otherwise, it will lead to large error.
It is essential to calculate the sag always before alignment and to be considered during calculations. For calculation of sag mount the magnetic tool holder firmly with the gauge on a pipe, adjust the dial gauge reading to zero with the sensor tip touching the pipe surface. Then turn the pipe 180 degrees and take the dial gauge reading, repeat the process another 180 degrees and take the reading, the difference in the two readings will give the double of the sag value.