Concentricity


Any two cylindrical surfaces sharing a common point or axis as their center are concentric. Any dimensional difference in the location of one center with another is the extent of the eccentricity.


It will be seen from the sketch that out of roundness in either diameter does not affect their concentricity because concentricity relates the centers or axis of the diameters. Out of roundness is their variance from a true circle. However, in a shaft or tube, straightness has a very real influence on concentricity.


_l I


A r-1 -----...,_ __


Diameters A and B may be true circles, but it is obvious that the out of straightness condition has affected concentricity.


Concentricity Tolerance


When the length of a bar or tube does not exceed its component diameters by a factor of more than 2 times, the component diameters will be concentric within .005" per l" of separation.


'B---~ l r--4"---i L ---- 3" = 2" Example A ~ .005" TIR Example B


EXAMPLE A- 3" OD x 2" ID x 4" long. 3" OD and 2" ID will be concentric within .005" TIR (3" OD - 2" ID = l" separation)


EXAMPLE B- 5" OD x 2" ID x 2" long. 5" OD and 2" ID will be concentric within .015" TIR (5" OD - 2" ID= 3" separation)


When the length exceeds the factor of two times, then the amount of out of straightness as described in a previous section should be added to the inherent eccentricity.


EXAMPLE 2" OD x l" ID x 4" long. Separation l", eccentricity .005" TIR 4" x .005" per l" out of straightness


Total of deviation


.020" TIR .025" TIR


7 ~2".j T 5"


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