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Bilateral positioning in PLTZF

Bilateral positioning in PLTZF

(OP)
Hello,

Is there a way to bilaterally locate a pattern of holes? That is have a circular feature to feature tolerance zone but a rectangular pattern tolerance zone? I've encountered this scenario a couple times. One approach is to individually tolerance each hole with composite feature frames like mentioned in this thread: http://www.eng-tips.com/viewthread.cfm?qid=344419 but this approach doesnt seem to be very scalable.

Any thoughts?

RE: Bilateral positioning in PLTZF

I agree with CH's proposal.

The problem may arise (for this particular part and datum features configuration) if the intent is to additionally orient the pattern to B within dia.005. In that case "classic" position callout won't work.

RE: Bilateral positioning in PLTZF

(OP)
Thanks CH, thats exactly what I was looking for!

RE: Bilateral positioning in PLTZF

I agree with CH's approach as well.

Certified Sr. GD&T Professional

RE: Bilateral positioning in PLTZF

I am still curious, what would you, guys, suggest if the intent was to additionally orient the pattern to B within dia.005, not within the width of .010?

RE: Bilateral positioning in PLTZF

I am having hard time visualizing circular tolerance zone restricting location in only one direction.

"For every expert there is an equal and opposite expert"
Arthur C. Clarke Profiles of the future

RE: Bilateral positioning in PLTZF

Not sure I understand what you mean.

In the scenario you proposed position callout dia .005 wrt A does not assure that the line connecting centers of both cylindrical tolerance zones is parallel to the datum center plane B. So my question is, how to control the paralellism without constraining location of both cylindrical tolerance zones to B?

RE: Bilateral positioning in PLTZF

So, it's good old floating tolerance zone.

I don't think use of composite will be forbidden in this situation.

"For every expert there is an equal and opposite expert"
Arthur C. Clarke Profiles of the future

RE: Bilateral positioning in PLTZF

So doesn't it bring us back to the OP's question - technically, how to specify composite position callout if the PLTZF is a pattern of bidirecional tolerance zones and the FRTZF is a pattern of cylindrical tolerance zones?

RE: Bilateral positioning in PLTZF

Quote (pmarc)

So doesn't it bring us back to the OP's question - technically, how to specify composite position callout if the PLTZF is a pattern of bidirecional tolerance zones and the FRTZF is a pattern of cylindrical tolerance zones?

Here's my thought:

To specify the bidirectional pattern-locating tolerance zones, use two single-segment positional tolerances.

To specify the cylindrical feature-relating tolerance zones, use either a single-segment positional tolerance with a SEP REQT note and with a customized datum reference frame that only constrains rotation, or use a regular composite positional tolerance where the tolerance value in the uppermost segment is so large that it does not provide any further restriction beyond that established by the bidirectional bidirectional tolerances.

pylfrm

RE: Bilateral positioning in PLTZF

pylfrym,
I was thinking about customized datum reference frame too. Just nor sure why SEP REQT would be needed.

The other idea is really interesting, although if this was my drawing, I would probably hesitate to go with it (unless the drawing was per prior-2009 version of Y14.5).

RE: Bilateral positioning in PLTZF

pmarc,

No need for SEP REQT on the example posted by CheckerHater. I was just trying to fully duplicate the rules of composite tolerances for the general case.

What changed in 2009 that makes you hesitant to use the second option?

pylfrm

RE: Bilateral positioning in PLTZF

Quote (pylfrm)

or use a regular composite positional tolerance where the tolerance value in the uppermost segment is so large that it does not provide any further restriction beyond that established by the bidirectional bidirectional tolerances.

Is this "the other idea" ?

I am trying to understand it myself....... the differences between 1994 and 2009.

RE: Bilateral positioning in PLTZF

Quote (pylfrm)

What changed in 2009 that makes you hesitant to use the second option?

Well, in 2009 they introduced the customized datum reference frame concept. In other words, they gave us a standard tool that offers a solution of the problem without a need of using this tricky composite callout that technically is... how to say it... partially redundant.

RE: Bilateral positioning in PLTZF

Looks like has been a confusion on what " the other idea" means. At least I was confused.

I initially believed that first option was the customized datum reference frame concept and the second idea (or "the other idea") was the regular composite positional tolerance.


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