huangyhg

tolerance analysis for large # of holes
i think this might be a dumb question, but does anyone know how to do a tolerance analysis on a large 10x9 hole pattern (90-.029 dia holes and 90-.016 dia pins)? all holes are +/- .002 from a reference point and all pins are +/- .002 from a reference point.
take a look at appendix b of asme y14.5m-1994. it will require you to convert the +- to positional but might help.
kenat, probably the least qualified checker you'll ever meet...
frankbamma,
if all your holes are located from the same datums, the number of holes is irrelevant. the tolerance analysis is not particularly difficult.
your clearance is .029"-.016" = .013".
when a fixed pin must pass through a hole, the hole and the pin each can shift by one quarter of the clearance. they each could shift at a 45 degree angle, so you divide your tolerance by sqrt(2).
.013"/4/1.414 = .0023"
your +/-.002" tolerance is adequate.
your required gd&t positional tolerance as recommended by kenat is one quarter of the clearance to get the maximum allowable shift, and multiplied by two because the positional tolerance is a diamter, not a radius.
pos = .013"/4*2 = .0065"
my calculations are based on your nominal values. if your nominal values are maximum material condition (mmc), then my numbers are correct. otherwise, my numbers are not correct.
the resulting tolerance zone is now a circle with about 1.4 times the area allowed by the +/- tolerances. this is the standard gd&t lecture, which will matter to you if you have troubles reaching +/-.002" tolerances.
jhg
kenat and drawoh, thanks for the help. your answere are exactly what i needed.
frank
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