Concentricity again
Concentricity again
(OP)
I am having difficulty explaining the difference between gd&t concentricity and t.i.r. to a foreign customer.
The application is a simple straightforward condition of diameter to diameter.
His position is this:
The callout on his drawing is concentricity (doubled circle symbol) = .008. His inspection shows Total Indicated runout of .010. He claims that this is concentricity.
I have tried to explain the ASTM definition of both, but to no avail.
My position is that in this case, T.I.R. approximates twice the out of concentric condition, and that his T.I.R. result should be divided by two.
Does anyone know of a simple definition for this premise that I can show my customer?
I am obviously not arguing with this guy, but I could use some help on this one.
Thanks
dbutka
The application is a simple straightforward condition of diameter to diameter.
His position is this:
The callout on his drawing is concentricity (doubled circle symbol) = .008. His inspection shows Total Indicated runout of .010. He claims that this is concentricity.
I have tried to explain the ASTM definition of both, but to no avail.
My position is that in this case, T.I.R. approximates twice the out of concentric condition, and that his T.I.R. result should be divided by two.
Does anyone know of a simple definition for this premise that I can show my customer?
I am obviously not arguing with this guy, but I could use some help on this one.
Thanks
dbutka





RE: Concentricity again
--Scott
For some pleasure reading, the Round Table recommends FAQ731-376
RE: Concentricity again
smr
RE: Concentricity again
Per ASME Y14.5M-1994 concentricity is defined as follows:
5.12.1 Concentricity Tolerancing. A concentricity tolerance is a cylindrical (or spherical) tolerance zone whose axis (or center point) coincides with the axis (or center point) of the datum feature(s). The median points of all correspondingly-located elements of the feature(s) being controlled, regardless of feature size, must lie within the cylindrical (or spherical) tolerance zones. The specified tolerance and the datum reference can only apply on an RFS basis. See Fig. 5-54. Unlike the control covered by para. 5.1 1.1, where measurements taken along a surface of revolution are made to determine the location (eccentricity) of the axis or center point of the actual mating envelope, a concentricity tolerance requires the establishment and verification of the feature’s median points.
Per ASME Y14.5M-1994 total runout is defined as follows for a “coaxiality” type of control.
6.7.1.2.2 Total Runout for Composite Control of Surfaces. Total runout provides composite control of all surface elements. The tolerance is applied simultaneously to all circular and profile measuring positions as the part is rotated 360". See Fig. 6-48. Where applied to surface, constructed around a datum axis, total runout is used to control cumulative variations of circularity, straightness, coaxiality, angularity, taper, and profile of a surface. Where applied to surfaces at right angles to a datum axis, total runout controls cumulative variations of perpendicularity (to detect wobble) and flatness (to detect concavity or convexity).
Using a TIR methodology to verify a concentricity specification is technically incorrect based on the standard interpretations. Yet, I see it done this way time and time again and parts that pass this check seem to work just fine in their intended application. This tells me that runout, and not concentricity, was probably the specification that should have been applied in the first place.
GDT_GUY
RE: Concentricity again