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Re: Position w/ bonus & bonus/shift of datums
Re: true position w/ bonus & bonus/shift of datums -- Kyle Kraft	Post Reply	Top of thread	Forum

Posted by: kelly_bramble ® 08/20/2005, 19:43:26 Author Profile Mail author Edit

There isn't a geometric tolerance called "True Position", the tolerance is called "Position". True position the actual measured position of a feature. There will only be one bonus tolerance relative to the specified datum reference frame (DRF). Your specification seems to indicated that when the hole feature is manufactured at the maximum material condition (MMC), or smallest hole allowed within the stated limits of size, that the tolerance zone is diametric or cylindrical shaped, oriented and located relative the DRF. As the hole feature diverges from MMC, then an increase in the allowed position tolerance is allowed equal to the amount of hole size divergence from MMC. So, you state that your bonus tolerance is "0.1", this indicates to me that the hole was manufactured 0.1 larger than the allowed MMC for the hole. Therefore; your acceptable position tolerance is equal to 0.25 + 0.1 = Diameter 0.35. Assuming datum A is a feature which is perpendicular to the hole feature, then you have a cylindrical shaped tolerance zone 0.35 in diameter, which is oriented (perpendicular) to datum A, and located a specified distance from both datum B and C by basic dimensions. The 0.35 cylindrical tolerance zone is at least as long as the hole is required to be, either thru to the next surface, or a specified depth. With this cylindrical tolerance zone, the derived center of the hole (axis) must within the inside boundaries of the tolerance zone at all locations. The "Bonus tolerance" given by the datums allows for a shift of the cylindrical tolerance zone equal to one half of actual cumulative divergence from MMC of the specific datum feature. So, you will have at least 0.1/2 = 0.05 for each datum feature plus one half any size divergence of the datum feature MMC. Assuming the datum are features of size specified at MC. If you leave off the position symbol, then you do not have a complete feature control frame, and the definition is incomplete. Modified by kelly_bramble at Sat, Aug 20, 2005, 19:53:28

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Re: Position w/ bonus & bonus/shift of datums
Re: Re: Position w/ bonus & bonus/shift of datums -- kelly_bramble	Post Reply	Top of thread	Forum

Posted by: Kyle Kraft ® 08/21/2005, 13:10:04 Author Profile Mail author Edit

Ok - I understand the first part about the 0.35 position tol. On the 2nd part where the dat A hole is 0.1 bigger than min. and the dat B hole is 0.1 bigger than min. I would get an additional 0.2/2 or 0.1 shift allowance allowing my total tol. for the feature to be 0.35 (origional position tol.) + 0.1 (shift tol.) for a total tol of 0.45 ?? Thanks, KAK

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