Machinery's Handbook, 31st Edition
Parallel Bars
755
Table 7. Calibration of Parallel Bar and Matched Parallel Bar Sets Straightness Surface A Nominal As Found As Left Tolerance Zero Setting (Point 1)
Cal Point 2 Cal Point 3 Cal Point 4 Cal Point 5 Surface B (under)
Nominal
As Found
As Left
Tolerance
Zero Setting (Point 1) Cal Point 2 Cal Point 3 Cal Point 4 Cal Point 5 Surface C Zero Setting (Point 1) Cal Point 2 Cal Point 3 Cal Point 4 Cal Point 5 Surface D (under) Zero Setting (Point 1) Cal Point 2 Cal Point 3 Cal Point 4 Cal Point 5 Sum Surfaces A + B A2 + B2 A3 + B3 A4 + B4 A5 + B5 Sum Surfaces C + D
Nominal
As Found
As Left
Tolerance
Nominal
As Found
As Left
Tolerance
Parallelism Calculations
Nominal
As Found
As Left
Tolerance
Nominal
As Found
As Left
Tolerance
C2 + D2 C3 + D3 C4 + D4 C5 + D5
Height and Width, Matched Sets.— The calibration of height and width of matched sets of steel or cast-iron parallel bars is a relatively simple process. Place the two parallel bars side by side on the surface plate in the same orientation, that is, with the same side up and the predefined calibration points adjacent to each other. One parallel bar will be desig - nated as “A” and the other as “B”. Position the height transfer gage next to the parallel bars and dial the transfer gage to the dimension of the side under test. Zero the electronic indicator on the transfer gage. Pull back the indicator probe off the land of the transfer gage and then replace it onto the land and ensure the zero setting repeats. If it does not repeat, re-zero the indicator amplifier and repeat the reading. Verify the zero setting in this manner until the reading repeats three times in a row with no variation. Then move the indicator probe to the surface of the “A” parallel bar and observe the deviation from zero reading. Sweep the entire surface and verify that all readings fall within the tolerance limits defined for the type and grade under test. Return the indicator probe to the transfer gage land and confirm that the zero point has not shifted before accepting the readings observed. If the zero point has shifted, it will be necessary to repeat the zero point setup and take the readings from the parallel bar again. If the readings are acceptable, proceed to the “B” parallel bar and verify that the deviation from zero reading is within the tolerance limits defined and the deviation from the “A” block is not beyond the limits for the type and grade under test.
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