Positional tolerancing

Positional tolerancing
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Posted by: Brutus ^®

02/23/2005, 18:41:53

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How do I figure positional tolerance when the feature of size is called out with respect to three datums with each datum having a basic location? I'm familiar with two datum (2X the square root of the sum of squares) but am unsure how to calculate three variables. I've heard several explainations, however, none seem valid.

Thanks for the help.

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Re: Positional tolerancing

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Posted by: traingdt ^®

02/28/2005, 09:22:35

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That is a tough one, but it really depends on whether the datum references are at RFS or MMC. If they are RFS, then the position tolerance is not affected (other than a possible bonus on the feature we are positioning). If they are MMC, then the tolerance on the datum itself may carry over to your other feature. But you can't really come up with one grand number, because the carryover effect from each datum will act in a different direction.
You said that each datum has a basic location, but is that taken from other datums, or to the feature we are positioning?

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