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true position calculations | |||
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Posted by: kep55 ® 02/07/2007, 18:07:25 Author Profile eMail author Edit |
I have a .005 tp to datum d, with datum d being 2 dowels. The feature the callout is attached to is the 2 dowels themselves. The calculated distance between the dowels is 83.03651 and the actual measurement is 83.0395. Would this produce a true position of .000 on the dowel to which the origin is set and .006 tp on the other or would I establish the origin at the midpoint and then have a .003 tp on both dowels? |
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Re: true position calculations | |||
Re: true position calculations -- kep55 | Post Reply | Top of thread | Forum |
Posted by: traingdt ® 02/08/2007, 17:17:02 Author Profile eMail author Edit |
First, I would say it's not quite right to reference datum "D" if the dowels themselves are "D". (However, it is common to reference a datum of the plane that the dowels project from, in order to cover perpendicularity.)
But as for your question, since the position is applied to both dowels, it doesn't matter which one you think of as your origin. Technically, the distance of 83.03651 establishes a fixed distance between two imaginary lines, perfectly parallel to each other. Then a tolerance is wrapped around each of those lines (was it .005 or .006?). Presuming there's a diameter symbol in front of the tolerance, then each dowel's actual axis can deviate in any direction from its perfect line by half of the given tolerance. So if they each go in opposite directions, the maximum measured distance cannot exceed 83.04251 (using the .006 number). The minimum would be 83.03051. So if no other datums are mentioned, it's basically a plus/minus of .006 of the perfect distance. |
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