runout tolerance 2

[1sds]

Why is it that a runout tolerance on a diametric feature always applies on an RFS basis; namely, size variation has no effect upon the runout tolerance compliance, if the diameter in question is a feature of size?

Thanks,
sds

 

[ewh]

Because runout is a measurement of circularity, not size.

 

[btrueblood]

Because runout is (usually) checked by rotating the part on the datum feature in a V-block (i.e. the datum feature is a bearing surface in the v-block).

 

[ctopher]

btrueblood,
wouldn't that be total-runout?

Chris
Sr. Mechanical Designer, CAD
SolidWorks 05 SP3.1 / PDMWorks 05
ctopher's home site (updated 06-21-05)
FAQ559-1100
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[TheTick]

ctopher:
Single runout = runout at any given section (2D circle zone at a point on an axis)
Total runout = runout over entire face (i.e. 3D cylinder zone)
Runout does not control size. It only controls the variation of movement when a part is revolved about a specific axis.

btrueblood:
Most texts I've read specifically say not to check runout in a V-block. A datum face's eccentricity can affect the runout reading as contact points in the V-block vary through the part's rotation.

In theory, I suppose runout can have an MMC modifier, but I have not encountered a situation where it was advisable to do so.

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[Heckler]

Building on TheTicks answer:

Circular Runout is a two dimensional, surface to an axis control. The tolerance is applied independently at each circular cross section. When applied to a surface constructed around a datum axis, circular runout will control cumulative variations of circularity and coaxiality. Unlike total runout , it doesn't control taper.

Total Runout is a three dimensional, surface to an axis control. Total runout provides a composite control of all surface elements. When applied to a surface constructed around a datum axis, total runout will control the cumulative variations of circularity, straightness, coaxiality, angularity, taper and variations in the surface.

I also second, that checking with a V-block is not a good inspection process

 

[MechEng13]

I would have to Third that checking for runout in a V-Block is not a good practice.

Runout does not care what size a piece is, only the variation from a Zero point.

In past lives we would try to always add centers to the ends of a piece we knew we would need to check runout on.



Alan M. Etzkorn
Reliability Engineer
Wabash National Corp.

http://www.wabashnational.com

 

[Hydroformer]

MechEng13-"I would have to Third that checking for runout in a V-Block is not a good practice."

And a fourth to that... There are tri-lobe shapes that will read 0.0 run-out in a 90deg V-block. I remember reading somewhere about using a 60deg V-block then a 90 and comparing the results.


*Without data, you're just another person with an opinion.*

Hydroformer