huangyhg

number of inspection places for width callout
i have a fairly simple callout for the width of a glass sheet (319.173 +/- 0.5 mm, one edge parallel to opposite edge within 0.3 mm). i am wondering if there is a minimum number of locations that the width needs to be measured. are they required to run a probe down the whole edge and report the max and min? is there a minimum number of locations to measure parallelism? if the edge is curved (i.e. the corners are even, but it bows in at the middle), would it still be called parallel? is the parallelism "best fit edge" created by finding the high points on the edge (taking a plate and resting it on the edge, essentially) or is it created by some kind of weighted average of a bunch of points?
whew, lots of questions. thanks in advance for any responses.
laura
what drawing standards are you working to, asme y14.5m-1994? there've been a few posts about parallelism lately and on one of them i put some information from 14.5.
typically the final verification of the part will be the responsibility of the inspection department. the standard establishes the parameters for geometry, but does not dictate the inspection methods to be applied.
this should apply to any/most drawing standards.

here are some quick answers and then a bit of explanation:
i have a fairly simple callout for the width of a glass sheet (319.173 +/- 0.5 mm, one edge parallel to opposite edge within 0.3 mm).
i am wondering if there is a minimum number of locations that the width needs to be measured. no
are they required to run a probe down the whole edge and report the max and min? no
is there a minimum number of locations to measure parallelism? no
if the edge is curved (i.e. the corners are even, but it bows in at the middle), would it still be called parallel? possibly
is the parallelism "best fit edge" created by finding the high points on the edge (taking a plate and resting it on the edge, essentially) or is it created by some kind of weighted average of a bunch of points? neither
the parallelism requirement is that all points on the toleranced edge must lie within a zone 0.3 mm thick. that zone is defined to be parallel to the "true geometric counterpart" of the datum edge, physically represented by a surface plate resting on the datum edge.
strictly speaking, the requirement is that all points lie within the tolerance zone. the method used to verify this, and the number of points sampled, is up to the inspector.
evan janeshewski
axymetrix quality engineering inc.
so if i want to require them to measure more than one location for width and parallelism, i need to create a note to say so?
thanks a lot for the quick answers, it helps.
you don't normally put dimensional inspection requirements on the drawing. (reference to statistical tolerancing is a partial exception i suppose.)
this is normally part of the quality plan or something, which may contain an annotated/marked up drawing.
kenat, probably the least qualified checker you'll ever meet...
yeah, it is more along the lines of putting it into work instructions.
matt lorono
cad engineer/ecn analyst
silicon valley, ca
if you add a straightness callout to one edge in addition to your parallelism, i would hope the inspector would at least measure both ends and the middle of the opposite side, but there is no guarantee.
there's always inspection fixtures...
"art without engineering is dreaming; engineering without art is calculating."
just curious, but could you explain a little more about the function of the glass and some info on how it is made.
i can't give you details, but it's a flat, thin piece of float glass that is being die cut to shape. the question was really more theoretical, and could apply to any part though.
to expound on what i put before with the drawing you're defining what you want. you don't generally specify how it's achieved (except when this overlaps with ensuring funcion - see asme y14.5 section 1.4e) or how it's verified.
kenat, probably the least qualified checker you'll ever meet...

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