Composite True Position Interpretation
Composite True Position Interpretation
(OP)
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
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





RE: Composite True Position Interpretation
Would you mind to post a sketch or print.
SeasonLee
RE: Composite True Position Interpretation
Here's a very rough sketch I drew up in Photoshop, as I'm at home right now, I don't have access to my CAD program. It should give you the idea though. I've simplified it a bit for the pic by removing a bunch of the holes.
RE: Composite True Position Interpretation
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.
http://www
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
RE: Composite True Position Interpretation
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.
RE: Composite True Position Interpretation
RE: Composite True Position Interpretation
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.
www.qmsi.ca
RE: Composite True Position Interpretation
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.
www.qmsi.ca
RE: Composite True Position Interpretation
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!
RE: Composite True Position Interpretation
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.
RE: Composite True Position Interpretation
Maybe another thread with a list of abbreviations?
Thanks
RE: Composite True Position Interpretation
Feature Relocating Tolerance Zone Framework - Plahtz
See ASME Y14.5M-1994 section 5.4
What is Engineering anyway: FAQ1088-1484: In layman terms, what is "engineering"?
RE: Composite True Position Interpretation
RE: Composite True Position Interpretation
I don't want to be picky but the FRTZF is really Feature Relating Tolerance Zone Framework per page 93 of the 94 standard.
Dave D.
www.qmsi.ca
RE: Composite True Position Interpretation
I am dyslexic though, does that get me any slack?
What is Engineering anyway: FAQ1088-1484: In layman terms, what is "engineering"?