What's the Formula for Concentricity?

Concentricity of what? Solid/hollow pipe etc.

Example(Concentricity of tube): C=100x (Wmin/Wmax)

Where Wmin=minimum wall thickness

and

Wmax=Maximum wall thickness

A quick Google search turned up the following:

http://www.bcmac.com/Tech%20Tips/Metrology%20Tips/M2.PDF

concentricity of bore(xx).

Datum Bores are G and L

specification of xx bore concentricity is 0.03 G-L

What do you mean by formula ?

It is a geometrical tolerance and what is the formula of a tolerance ? it is a required feature of a component, like any other features.

What is the formula of length ?

What is the formula of length ?

L = L, where L is the length in question.

Glad I could be of help.

Could you please your definition of concentricity because the way you write the formula it is something wrong in the understanding of the notion. If you do not correct it none of the explanations will be clear to you. So the best is you write what is concentricity for you and we have a basis to discuss.

I think he means he doesn't know how to measure it: He's looking at a drawing spec of 0.03.

In which case, the answer is...

"fill in the details, Watson!" (from the movie: Without a clue)

Sorry for the bad humour, OP, but this is pretty basic stuff. You should really read a book on tolerances.

p-x

This is how I'd measure what you ask.

Mind the RFS comment about concentricity. A FIM will not do you any good here: You need to consider the theoretical centres.

By the way, most of the time drawings specify concentricity tolerances for features of size where a positional tolerance (likely with a MMC/ LMC call-out) would best have served the design intent... Said tolerance would be much easier to measure too.

I hope this helps

The problem with dial reading is it gives the Run-out value .

ie

Not true in this case. You are referring to a similar but different use of the indicator. That is exactly why the OP should not read the FIM value (used for the runnout), but instead record the actual distributions of read-outs as sketched. In effect, by zeroing the dial at the nominal D, he will be making cylindrical coordinate measurements (radial measurements at regular angular intervals), as is appropriate for determining cross-sectional centres and therefore concentricity.

One may also ref. to, i.e.: W. Boyes (Ed.), Handbook of jig and fixture design, 2nd Ed, SME, 1989

Regrettably, in the absence of a convenient CMM, the OP will have to make do with the dial, as awkward as that may be...

The obvious answer is that two arcs share the same center point.

If you are asking how to determine if two curved surfaces are concentric, first you must measure the data points on the surface to produce the curve data, which can be plotted on xy graph.

Next is plot the center for each graph for each curve, and then to compare those center coordinates.

If the coordinates are the same, then the surfaces at the points measured are concentric.

If it is not this scenario, then please provide more information in your query.

Chris

If you are dealing with a pipe, then either the ID or OD will be your datum. Concentricity is the distance between the respective centers. On a comparitor. measure your datum diameter first and set your X and Y scales to 0.0 at the center. Then measure the other diameter and note the location of its center. X and Y values are the sides of a triangle. The hypotenuse is your concentricity. On a CMM, just make your datum diameter the X Y origin. Measure the other diameter and it will report the new center.

If neither of these devices is at your disposal, then first make sure your datum is in fact round. Do the same for the other diameter. If in fact both are round, measure the wall thickness. Concentricity is on half the total change in the readings.

the OP was *^&% rude and never came back...

He is by far no exception. I met only a very few people saying "thanks" or giving an information how the comment did help.