Concentricity vs Runout
Concentricity vs Runout
(OP)
Our shop produces shafts. The shafts have 3 stepped diameters at each end. The designers have been using concetricity callout on the shaft diameters in relation to one of the bearing journals.
From any research I do it says to not use concentricity if at all possible, since most shops are unable to accuratly measure it.
What is a good method for using geometric tolerancing on a shaft with multiple turndowns to ensure it can be accuratly reproduced if contracted out? Should they just be using runout?
An example of a typical shaft may be a 5" diameter for the majority of the center portion, turned down at each end to a 4" diameter, then a 3" bearing journal, then a 2.5" drive journal. One 3" bearing journal would be the datum. With all other journals wanting to be inline to it.
Sorry if this is a very basic question.
From any research I do it says to not use concentricity if at all possible, since most shops are unable to accuratly measure it.
What is a good method for using geometric tolerancing on a shaft with multiple turndowns to ensure it can be accuratly reproduced if contracted out? Should they just be using runout?
An example of a typical shaft may be a 5" diameter for the majority of the center portion, turned down at each end to a 4" diameter, then a 3" bearing journal, then a 2.5" drive journal. One 3" bearing journal would be the datum. With all other journals wanting to be inline to it.
Sorry if this is a very basic question.
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Randy





RE: Concentricity vs Runout
You may have to force your designers to dig deep to understand the true meanings of concentricity vs. runout. Once they do, it should be no problem.
RE: Concentricity vs Runout
On all the parts I’ve designed lately where ‘concentricity’ is an issue I’ve used a combination of run out and/or positional tolerance. The senior design checker here helped me with it, and he does know GDT well.
The positional may not be relevant to your application but I think it’s probably worth looking at as an option as well as run out.
Ken
RE: Concentricity vs Runout
Chris
Systems Analyst, I.S.
SolidWorks 06 4.1/PDMWorks 06
AutoCAD 06
ctopher's home (updated 06-21-05)
RE: Concentricity vs Runout
A spinning shaft mounted in bearings is a fairly common part spanning many industries. I was hoping there was a common prefered method for dimensioning it.
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Randy
RE: Concentricity vs Runout
RE: Concentricity vs Runout
"Concentricity is a control of one axis to another. It is always applied on an RFS basis. The use of any other modifier is incorrect.
A very small number of tolerancing applications call for a concentricity tolerance. The tolerance should only be used when the location of one axis to another needs to be accurately controlled. Concentricity should only be applied when it is certain the axis relationships are the only means of producing a functionally acceptable part. verifying concentricity tolerances is very difficult when using manual inspection equiptment.
Most coaxial requirements can be met with either a position tolerance at MMC or a runout tolerance at RFS. These tolerance types can both be easily checked on the basis of surface conditions. They are preferable to concentricity requirements because of the ease in verifying position and runout tolerances. Concentricity should only be used when absolutely nessesary.
There are many applications where concentricity is incorrectly applied, and runout is the control the should have been applied."
RE: Concentricity vs Runout
So I'm left with runout, total runout, or position, or a combination of these which is what i was hoping was the correct method.
Is the proper method to use either total runout, or position at mmc, or both?
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Randy
RE: Concentricity vs Runout
RE: Concentricity vs Runout
RE: Concentricity vs Runout
There has been talk about removing symmetry and concentricity from the next revision of the Y14.5 standard because it doesn't provide any functionality that can't be achieved better by other controls separately or together, and because there really is no practical way to verify it.
Jim Sykes, P.Eng, GDTP-S
Profile Services
CAD-Documentation-GD&T-Product Development
RE: Concentricity vs Runout
TheTick was correct about designers and inspectors.
Chris
Systems Analyst, I.S.
SolidWorks 06 4.1/PDMWorks 06
AutoCAD 06
ctopher's home (updated 06-21-06)
RE: Concentricity vs Runout
One site I looked at used both runout and total runout to define one circular feature with respect to another ...http://www.tec-ease.com/tips/march-00.htm
The same site shows circular runout alone being used to define circularity and concentricity.... http://www.tec-ease.com/tips/june-97.htm
From looking at those examples, I should be using both circular and total runout as in the first example above. Does that sound like the proper method to you folks?
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Randy
RE: Concentricity vs Runout
Looking at the first reference (March '00), notice that the two controls have different tolerance values; specifically, the Total Runout has a larger tolerance zone than the Runout. So, the overall variance is larger than the variance at the each individual cross-section (which is where Runout is applied).
The second reference only shows the topographic view (an edge), so no depth is idicated; as a result, Total Runout cannot be indicated until an actual surface is shown.
As to which to use, if the length of the cylindrical surface makes it difficult to maintain a constant diameter, then use both controls. If the cylindrical surface is short, then Total Runout alone should be adequate.
Hope that helps.
Jim Sykes, P.Eng, GDTP-S
Profile Services
CAD-Documentation-GD&T-Product Development
RE: Concentricity vs Runout
In the first link, if you just used total runout, you could have a variance at any one POINT of up to .15 as long as the overall variation for the entire surface did not exceed .15. On the other hand just using the runout tolerence, you can only have a variation of .05. The problem with that is that it only controls the size at any given point not the shape of the whole surface. By using both, more importantly the total runout first, You can loosly control the overall shape of the surface and but prevent drastic variance at individual points.