Is it correct to measure shaft roundness and bearing clearance in this way?
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This post was last edited by kulouand on 2016-1-26 at 08:47. As the title suggests, when performing inspections, the roundness of the shaft journals is measured; experienced workers simply use a dial indicator to take readings at two positions that are 90 degrees apart from each other, namely the top and bottom as well as the left and right of a cross shape, and then the difference between the maximum and minimum readings gives the value indicating the degree of roundness. The same method is used for measuring the inner diameter with an inner-diameter dial indicator for the bearing inner ring. Finally, by subtracting the two sets of values for the shaft from the two sets of values for the bearing inner ring (the maximum and minimum values respectively), the clearance is obtained. Is this method correct? How did you measure it? Also, what are the commonly used standards for the maintenance of mechanical pumps? Thank you all.
The measured clearance and the circularity of the shaft are different. What is a micrometer used for?
This method is correct, simple, and practical. Learn well from the experienced craftsmen*; measurement isn’t something to be done casually. That’s how inspections and measurements are carried out at work.
The diameter of the measured shaft is determined using an outer diameter micrometer; after supporting it to ensure cylindricality, a dial indicator is used to make one full rotation, and the maximum value is then subtracted from the minimum value
The method is correct, but not precise enough. More points need to be selected to calculate the difference between the average inner diameter and the average outer diameter. Especially for the inner diameter of the bearing, since deformation is likely to occur at the bearing surface, the bearing clearance should be kept at its minimum value.
It can be used as a reference for assembly with low requirements, but it definitely won’t work for applications that demand strict standards.
Under normal conditions, when the journal is not worn, there will be no significant deviation in roundness. It is possible to measure the diameter in two perpendicular directions; when using a dial indicator to measure the inner diameter, the maximum reading from the dial indicator should be taken. Additionally, the fit between the bearing and the shaft journal is a transitional fit that tends to be interference-type; if there is any clearance, it should be very small, with a greater degree of interference. Otherwise, the inner ring of the bearing can easily slip, causing damage to the shaft journal.