Another concentricity vs runout thread
Another concentricity vs runout thread
(OP)
I realize there has been several of these threads but the more I read the more I get confused. Unfortunately there is no one where I work to go to with these questions. For the longest time I was always under the assumption that "concentricty for the most part will be half your tir" assuming round features (center point to center point). Then I read this article
http://w ww.manufac turingcent er.com/too ling/archi ves/0106/0 106concent ricity.asp
Is it correct to say that having a perfectly round part with perfectly round features will give you the same result for tir and concentricity or would the concentricity be half the tir?
http://w
Is it correct to say that having a perfectly round part with perfectly round features will give you the same result for tir and concentricity or would the concentricity be half the tir?





RE: Another concentricity vs runout thread
The simple fact is that if you are measuring TIR (i.e. deflection on mandrel) then you are not measuring concentricity, you are measuring runout. In almost all cases, runout and diameter are sufficient definition for both form and function.
To truly measure concentricity, one must measure the full form of the datum and the feature to determine effective centers. Even then, this does not guarantee runout, as the runout would also depend on the circularity of each of the surfaces.
RE: Another concentricity vs runout thread
RE: Another concentricity vs runout thread
The concentricty has a diametrical tolerance zone called out.
RE: Another concentricity vs runout thread
RE: Another concentricity vs runout thread
don't all concentricty callouts have a diametrical tolerance zone called out? should the end result be concentric within .023, not .046?
RE: Another concentricity vs runout thread
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RE: Another concentricity vs runout thread
RE: Another concentricity vs runout thread
2. so the statement that I hear a lot that "in general tir is double concentricity" is false? (assuming roundness is perfect).
RE: Another concentricity vs runout thread
On a perfect diameter, fully offset within the example zone, the full indicator movement would registar 0.04
Another way to think of it, concentricity is identifying the center axis of the feature, where runout is more concerned with the surface of the feature.
TheTick's example of two ellipses perfectly on center give you a concentricity measurement of 0. The runout would return the difference of the major and minor.
In general, ASME Concentricity seems best applied to spinning parts which require balance.
RE: Another concentricity vs runout thread
Position RFS had greater latitude in that the toleranced features were not required to be coaxial with the datum features and the shape of the zone could be described other than round "cylindrical" either by the depiction of leader lines or the absence of a diameter symbol.
Runout unlike position RFS or concentricity, does not consider a feature's "estimated axis, center, or central tendency" but rather its form and "estimated axis, center, or central tendency" simultaneously. As stated in the article you cited "if the feature is perfectly round" the summations are equivalent...if not they are not! Form errors will always increase the measured value for runout! The prerequisites for specifying Runout are like those for concentricity in that the toleranced feature must be coaxial to the datum feature(s).
In attempting to create a distinction for the evaluation of Concentricity in the Y14.5.1-1994 Mathematical Definition and subsequent Y14.5M-1994 Dimensioning and Tolerancing the committees abandoned the "estimated axis, center, or central tendency" for concentricity and replaced it with a surrogate "midpoints of opposed surface elements". That definition, however well-meaning or intended, has rendered concentricity impotent in constraining features with asymmetrical balanced forms such as odd tooth gears, multi-lobbed cams, etc.
The 1982 Y14.5 included a note of caution about specifying concentricity because of the difficulty in determining the center or central tendency of a feature... HOW IS THAT ANY DIFFERENT FROM DETERMINING THE AXIS OF A FEATURE????
Bottom line if the feature is coaxial, perfectly round, and perfectly oriented to the datum features and but off location… Position RFS = Concentricity = Runout = Total Runout