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Re: True position calculation

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Posted By<" ">Randy Kimball on April 14, 2002 at 09:18:53:

In Reply to: True position calculation posted byjpeak on April 12, 2002 at 21:27:59:

: Why is true position of a feature calculated as twice the distance (not just the distance)between the dimensioned exact position and the actual position?

Also: Don't confuse true position as a linear measurement system. We are talking about a system that is designed to control the positions of several features with respect to each other so that the mating part will fit. This is especially true of parts that must mate with their mate in the field with complete confidence in interchangeability. Therefore the system is designed to be a strict tolerance controling method, not a linear tolerancing method. Each time you add in an additional feature the effective misalignment grows. Example, it you have a hole pattern of eight holes, you must increase the size of the holes OR use true position to control the pattern or both of BOTH parts. Else, if just two holes are slightly off position the fit goes away in a hurry, "about" TWICE AS FAST as the error in position. Thus you question.

-randy-

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Subject: Re: Re: True position calculation

Comments:: : Why is true position of a feature calculated as twice the distance (not just the distance)between the dimensioned exact position and the actual position? : Also: Don't confuse true position as a linear measurement system. We are talking about a system that is designed to control the positions of several features with respect to each other so that the mating part will fit. This is especially true of parts that must mate with their mate in the field with complete confidence in interchangeability. Therefore the system is designed to be a strict tolerance controling method, not a linear tolerancing method. Each time you add in an additional feature the effective misalignment grows. Example, it you have a hole pattern of eight holes, you must increase the size of the holes OR use true position to control the pattern or both of BOTH parts. Else, if just two holes are slightly off position the fit goes away in a hurry, "about" TWICE AS FAST as the error in position. Thus you question. : -randy-

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