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Composite Position of bore pattern - ASME


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The first segment in the composite tolerance is Pattern locating tolerance where Translation and rotational degrees of freedom are constrained, they are not free to translate or rotate. So, we should not activate translation or rotation in the Best fit of bore menu.

The second segment in the composite tolerance is Feature locating tolerance where Rotation is constrained, but translation is not constrained. Part is free to translate. So, we should activate only translation in the best fit of bore menu.

If in the second or third segment, where no datum is specified, the part is free to translate and free to rotate, so we should activate translation and rotation in the best fit of bore menu.

Am i understanding correctly?

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Everyone seems to missing the MMB on the Datum C feature. As the datum C feature departs from its maximum material boundary, the position of the pattern is allowed to shift or translate. And because there is no tertiary datum or "timing" feature, the pattern is allowed to rotate, as well.

On the second tier, both translation and rotation are allowed.

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Just to further back up Tom's point here that seems to be getting overlooked--When an MMB(it's still called MMC though in the 1994 standard) modifier is applied in the composite tolerance, in the upper segment or PLTZF(Pattern locating tolerance zone framework), you do want to check those rotation and translation boxes, but you must have MMC selected on the datum feature along with the "View Tolerances" drop down active. This will only allow shift based on the size of the datum feature.

Then the lower segment or FRTZF (Feature Relating Tolerance Zone Framework.), you will check all those boxes again, but leave out the secondary datum all together. This will allow the part to shift any amount necessary, completely eliminating any constraints that could be established by the secondary datum.

Another thing to keep in mind is the simultaneous requirement that could be invoked here. If there are other tolerances of position or profile with the same exact datum reference frame, and the same modifiers as the DRF in the PLTZF does, there is a simultaneous requirement. So wherever the part shifts within the DRF, all the position and profile tolerances with that same DRF apply at that same shifted location. (Just a note: theres no simultaneous requirement for the FRTZF)

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We can refer to ASME Y14.5 - 2018 Section 10.5.1.8 and figure 10-41 to 10-46.

It looks like, rotation and translation will be constrained or not, does not depend on datum's boundary condition.
It only depend on, whether it is PLTZF or FRTZF.
Hello guys,
thank you for your answers, but i have final question. What is correct?

The Top tier miss third reference => i think the bore pattern rotation should be enable
The bottom tier is correct => i think the bore pattern rotation should be enable and bore pattern translation should be enable

Do i have right?

Regards
Lukas
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