Maximum allowed eccentricity for any shaft or hole diameter

rnsvasan

Involved In Discussions
#1
Hi,
Is there any thumb rule or standard that specifies maximum allowed eccentricity for any shaft or hole diameter. for an example if my hole diameter tolerance is 21 microns, then how much i can allow eccentricity if there is no any specification given by the customer.

Thanx in advance
 
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falconer65

#2
The rule of thumb would be the diameter needs to measure in specification no matter where it is measured. But a tolerance of 21 microns with no roundness or cylindricity call out? The real questions are, what is the application and what does the customer expect?
 

AlanC

Involved In Discussions
#3
we would normally go for half the tol as thumb, but if roundness is being measured then its not just the tolerance but the shape of the roundness which is also important which can highlight issues, especially if the hole as a keyway in it, in which case the roundness can be looked at locally away from the keyway. We would also apply half the tol rule mainly for bores/shafts that form part of an assembly as a concentricity tolerance since this is typically what comes out from bearing calcs, but if its not called for then stay away
 

Stijloor

Staff member
Super Moderator
#4
Hi,
Is there any thumb rule or standard that specifies maximum allowed eccentricity for any shaft or hole diameter. for an example if my hole diameter tolerance is 21 microns, then how much i can allow eccentricity if there is no any specification given by the customer.

Thanx in advance
Eccentricity is a location error. Are you referring to a possible circularity or cylindricity (form) error? In the USA according the ASME Y14.5 standard, "Rule #1" states that the limits of size control dimensional as well as form deviations. At Maximum Material Condition (MMC), form shall be perfect. ISO standards subscribe to the independency principle and state that form does not have to be perfect at MMC unless the "envelope principle" is invoked by used the "E" modifier.

Stijloor.
 
N

NANDAKUMAR_A

#5
Hi Srini,

The general understanding is one third of the Tolerance can be taken for the Roundness / Form parameters. However the application is also to studied to use the same.
 
M

Mr.Happy

#6
Hi,

An other question cums up, If roundness is measured (we also use half the tolerance) then how many measuring point do you choose (using CMM) and on what is this based ?
 
L

Livika

#7
Hi,
Is there any thumb rule or standard that specifies maximum allowed eccentricity for any shaft or hole diameter. for an example if my hole diameter tolerance is 21 microns, then how much i can allow eccentricity if there is no any specification given by the customer.

Thanx in advance
The eccentricity (as I know it) is always referred to something (for example eccentricity of hole referred to external diameter in case of bushing, eccentricity of shaft diameter referred to centers or another diameter) and does not depend on the tolerance of the specific diameter. But maybe you should specify what exactly you mean with eccentricity.
 

Michael_M

Trusted Information Resource
#8
Hi,

An other question cums up, If roundness is measured (we also use half the tolerance) then how many measuring point do you choose (using CMM) and on what is this based ?
Not using a standard to decide this, but when I check roundness (of a hole) using the CMM, I use a minimum of 12 points. This measures the diameter every 30 degrees. If speed is not a factor or I can afford to add a bit of inspection time, I will increase this to 16 (22.5 degrees) or 24 (15.0 degrees). I typically stick with 12 points.
 
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