huangyhg

runout tolerance
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
because runout is a measurement of circularity, not size.
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).
btrueblood,
wouldn't that be total-runout?
chris
sr. mechanical designer, cad
solidworks 05 sp3.1 / pdmworks 05
ctopherfff">:
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.
btruebloodfff">:
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.
i could be the world's greatest underachiever, if i could just learn to apply myself.
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
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.
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.*
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