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Composite True Position Interpretation 1

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cjohnso0

cjohnso0

Mechanical
Jul 17, 2001
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I've been scouring the internet all afternoon looking for some insight into a true position callout we are dealing with.

I am trying to inspect a threaded hole pattern (20 holes equally spaced around a circle) to the following composite true position:

[TP|0.0157|E|C]
[ |0.0157]

Datum -C- is a diamter, along the same axis at the bolt circle, while Datum -E- is a diameter, which is perpindicular to the bolt pattern, with the axis intersecting that of datum -C-

From my understanding, the top portion of the FCF is the position of the bolt pattern. This would check every hole's position in relation to -E- and -C-

The second portion of the FCF is what is confusing us here, with the tolerance the same as the upper portion, is there really anything additional to inspect?

If anyone has any insight as to what this means, or how to best inspect it (we've been using a CMM, but I don't think it takes the second part of the FCF into account). Does the second component yeild a 'bonus tolerance'?

Thanks in advance
 
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1. There are two problems on your composite position callout :
First, the tolerance zone is a cylinder located at the true position of each hole, so the diameter symbol should be added both at PLTZF and FRTZF.
Second, the tolerance value of the lower segment must always be a refinement of the tolerance value of the upper segment, so the tolerance value at lower segment should be smaller than .016.

2. I will recommend you to go through this thread and I believe you will have the answer from Mr. Jim Sykes’ posts.

3. I will recommend you to convert bolt circle diameters to coordinates for inspection of each bolt circle, attached chart is very useful.

4. There isn’t any material modifier MMC or LMC on the FCF, so no bonus tolerance will be yielded.

SeasonLee
 
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Thanks for the quick reply SeasonLee. I'm still confused as to how to interpret this. I may have to go back to the OEM who made up the print for this one to try to get clarification.

In regards to (1.) above, there actually is a diameter symbol on the drawing, I missed it. According to the drawing both PLTZF and FRTZF have the same 0.016 requirement.
 
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Sorry but the datums are incorrect and one cannot confirm the hole position as it stands right now with the biggest problem being datum B as a thru hole. We need a plane.

The primary datum should be the face and not the ID as shown. The secondary should be the ID which is shown as the primary. The through hole should not be a datum in this situation.

The top section of the composite feature control frame is the pattern location (PLTZF) relative to the datum structure. It can be confirmed quite easily now.

The bottom section is within the pattern (FRTZF)but just at the top of the features. If one had it referencing datum A as I suggested, then each of the holes can be confirmed not only at the top but also at the bottom.

Hope this helps.

Dave D.
 
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My previous answer is not totally correct. One can check the pattern relative to the primary and secondary datum as shown but is the datum setup practical.

Is either face of the part mounted on the mating part? If it is, then the face should be the primary datum with the secondary as the centre hole and the tertiary datum (for clocking around the secondary) as the hole perpendicular to the centre hole. I believe that this would be a better datum structure.

Dave D.
 
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dingy2 - This part is not mounting on the mating parts. Unfortunately, we didn't come up with this True Position callout, the part manufacturer somehow put it on their blueprint. We are repairing this part with weld, and need to inspect it after the welding process to ensure it's still serviceable.

I'll be contacting the part manufacturer on Monday about this one. In actuality, there are several bolt circles on the real part at various locations, and according to the blueprint, the majority of them have a similar True Position requirement.

Thanks for the help so far!
 
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The part is completely constrained by the two datums. The A datum constrains the part in the x and y direction as well as rotations about the x and y axes. The hole clocks it. It's odd, but perhaps the flange is like a packing gland where it doesn't mate against a face, and is located and oriented with respect to the flange bore.

As mentioned above, the tolerance zone shapes should be cylindrical, so a diameter symbol should preceed the tolerance.

The first line locates the pattern, the second the interrelationship between them. It appears to me, that even with the same number in them, it is not wrong. Just a waste of ink to write the extra lines.

Of course, as stated, the symbol could be replaced with a single one line location (true position) callout which would locate the pattern and it's individual elements in one shot and better describe engineering intent.

It sounds like the person applying the symbol was unclear about their functional needs.
 
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I'd hate to start a new thread, but can someone explain to me what PLTZF and FRTZF stand for?

Maybe another thread with a list of abbreviations?

Thanks
 
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Pattern Locating Tolerance Zone Framework - Fritz
Feature Relocating Tolerance Zone Framework - Plahtz

See ASME Y14.5M-1994 section 5.4

Posting guidelines faq731-376 (probably not aimed specifically at you)
What is Engineering anyway: faq1088-1484​
 
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