yang686526

runout vs. flatness
i have a print of a part that is similar to a cylinder. one flat end of the cylinder has a flatness tolerance. the other end has a circular runout tolerance.
i think i understand circular runout if it is applied to the curved part of the cylinder. but i don't see how it applies to the flat surface of the cylinder. and if it does, how does it differ from flatness?
the runout tolerance uses the other flat surface as its primary datum. it uses an outer diameter as its secondary datum. the print appears to have been created in the late 1960's.
i appreciate your help.
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i think it is in error. i don't see how the part can be inspected to runout from a curve and a flat surface.
time to revise the dwg to current stds.
chris
sr. mechanical designer, cad
solidworks 05 sp3.1 / pdmworks 05
i agree with chris as usual. your flat datum surface has no axis about which to measure runout. the cylinder should be the primary datum (controlled with cylindricity), then both ends can be inspected for runout relative to it.
or you can control the perpendicularity of the cylinder to the flat surface, but you would still need to control cylindricity. the other end could then be controlled with runout relative to the cylinder.
if the flat feature at the end of the shaft doesn't have to be positioned to any other feature or datum then the flatness call out seems to be in line. but if their need to clock that feature to something on assembly, another feature or datum then best use true position.
i would change the runout to just the axis of the shaft not the flat. using the flat and axis as a datum seems to wrong.
best regards,
heckler
sr. mechanical engineer
sw2005 sp 4.0 & pro/e 2001
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perhaps they're looking at it like a phonograph needle scenario (re
i agree with thetick (spoon!)
the flat end of the cylinder is your main datum, placed on a turntable concentric with the axis of the cylinder and turntable, then runout is measured at the other end.
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a runout tolerance always has a datum reference. a flatness tolerance never has a datum reference. see fig. 6-50 in the standard and related text for an example of runout callout with a planar primary datum and diametrical secondary datum.
based on asme y14.5m-1994, section 6.7 runout, a runout specification on the flat end of your cylinder is valid.
you say that the runout uses the opposite surface and the diameter as datums, which is appropriate. your inspector should jig up the part and run a dial indicator on the flat surface. the runout specification indicates the maximum full indicator movement (fim).
the only problem i can see is that asme y14.5m-1994 was not active in the '60s. your original designer may have meant someting else.
jhg