huangyhg

drafting tips for perpendicularity (tolerances)
hi,
i'm a materials engineer, with little experience of technical drawings, so i'm a little stuck. i need to find the nominal value and tolerance values for a feature.
i have the perpendicular symbol, with 0.03 after it. does this mean that the inspection values are...
nom 0
lower limit -0.03
upper limit 0.03
or
nom 90*
lower limit 89.97*
upper limit 90.03*
i wish i had a copy of drafting for dummies! i searched on the 'net, but i need it explaining in laymans terms...
cheers,
rich
if the feature control frame is properly constructed with the perpendicular symbol, .03 and then the datum, then essentially, the perpendicular surface must lie between two parallel plans that are .03 a part and are perpendicular to the specified datum. .03 represents the total tolerance zone, so it would be +.015, -.015 from basic.
matt lorono
cad engineer/ecn analyst
silicon valley, ca
rich,
is the perpendicularity applied to a cylindrical hole or to a flat surface?
in either case, perpendicularity is not a plus/minus tolerance and is not an angle that is measured in degrees. it is the size (thickness) of zone that the feature just barely fits into, and the zone is constrained to be exactly square to the datum feature. a perfect feature has a perpendicularity value of zero, and the value goes up as the feature tilts. there is no negative value.
nominal 0
upper limit 0.03
lower limit n/a

evan janeshewski
axymetrix quality engineering inc.
hi,
thanks for the help so far. i understand a lot better, however,axym and fcsuper, they seem to contradict each other?
rich
evan states that there is no negative value, while matt mentions a +/-.015 value. they are both correct, but you have to consider the value as absolute, with .015 available on both sides of the perfect feature.
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fcsuper was just trying to reply in the same terms in which you asked the question in order to keep it simple. he understands that there really isn't a +/- value. keep in mind that with perpendicularity, the actual feature can even be bowed, just as long as all parts of the feature remain within the .030 tolerance zone. a case like this would make an angle or a +/- condition difficult to verify. if the feature is a hole, it can be a little easier to check by using a gauge.
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ok, thank you all very much for your help! it's sorted now, cheers, rich
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