Composite TP questions 1

[cjccmc]

I have been asked to revise a data set that has a composite TP callout on two holes in-line as:
2X DIA .250-.253
TP DIA .030 /A/B/C
DIA .005 /C

The two holes are drilled normal to the flat datum C surface, so I can see why they want them perpendicular to C, but is it legal to make C primary in the lower frame when it is third in the upper?

As a separate question, is it legit to have a three line composite block? I had someone show me this several years ago who stated it was an "extension" of 14.5. It was used in a situation with multiple holes in line where you can allow say: .030 for the group, .010 perpendicular to datum A, but need all holes in-line by .002 The composite block would have the following for this:

TP DIA .030 A/B/C
DIA .010 A
DIA .002

I guess you could achieve the same with the first and third line shown above in a more typical two line composite and then apply a separate perpendicular DIA .010 /A. True? I like the look of the three line block, seems a bit more elegant than slapping that extra perpendicular FCF below the two line TP.

 

[PaulJackson]

See Attached

 

[axym]

cjccmc,

The separate Perpendicularity to A would apply a slightly different control than the Position to A in the second segment. Perpendicularity applies to each feature individually, so there would be two zones that would not be constrained to be coaxial to each other. Each zone would be perpendicular to Datum A, but each could float independently of the other. The coaxiality refinement in the third segment minimizes the impact of this, however.

Evan Janeshewski

Axymetrix Quality Engineering Inc.

http://www.axymetrix.ca

 

[fsincox]

Paul,
Nice graphic

 

[cjccmc]

Thanks for the visual aid Paul! It was more than I could digest at first but now I see the difference in the various callouts that might seem applicable. Now when I re-read 5.4.1 (1994 std) the words make sense.

I couldn't find any example of the 3 line composite in 14.5 I want to use it on a dataset I'm preparing but it's likely to get some questions around here as to legality. Is there any verbage in the std that supports it?

 

[Belanger]

If you have the 2009 edition, check out Figs. 7-44 and 7-45 (page 140).

John-Paul Belanger
Certified Sr. GD&T Professional
Geometric Learning Systems

http://www.gdtseminars.com

 

[SeasonLee]

cjccmc

Y14.5M-1994 only allow 2 segments on the composite position control, but it changed in 2009 standard, the new standard allows more than two segments as J-P mentioned above.

There is a composite position tolerancing rule according to Alex’s “Advanced concepts of GD&T”:
Any datum references and datum modifiers in the lower segment must be repeats and in the same order as the datum references and datum modifiers of the upper segment. So your concern is right, datum C cannot be as a primary in the lower segment.

SeasonLee

 

[cjccmc]

Thanks again all. I'm stuck with the 1994 std. Probably be 2023 before we adopt the 2009 if past is prelude

Does 1994 also limit the number of stacked single line TP to two? If not I can go with the three single lines that Paul illustrated on his sheet 1.

Other option seems what Evan described, but I would need to have the second line of the composite with no datum reference and again I'd be doing something I can't find an example for yet it seems correct in principle. So the two line TP composite with the Perpendicular below would look like:

TP DIA .030 A/B/C
___DIA .002
PER DIA .010 A

Is that as good as I can get it for what 1994 allows?

 

[bxbzq]

SeasonLee,
Can you direct me where in the '94 std it states only 2 segments allowed in a composite position control?

 

[SeasonLee]

bxbzg

Very good question, I quoted from composite position tolerancing rules from Alex's “Advanced concepts of GD&T” page 19-9, rule #2 states "A composite position control can only contain two segments".

Actually, you may find out the same statement from 94 std at page 95 top left : The position symbol is entered once and is applicable to both horizontal segments.

BTW, there is no limit on the maximum number of segments for multiple single-segment position tolerancing. but it rarely contains more than three segments in application, however it must have two segments at least.

SeasonLee

 

[Belanger]

I would say that you can have more than two, even in the 1994 rules. Those examples convey the idea of having the lower segment control only orientation to the datums (in addition to the hole-to-hole location, of course).

So what would be problematic about fine-tuning the orientation to two datums, and then just one? This would create three segments. Granted, there's no fancy acronym such as PLTZF or FRTZ, but to me this seems like one of the easier paths called "extension of principles."

John-Paul Belanger
Certified Sr. GD&T Professional
Geometric Learning Systems

http://www.gdtseminars.com

 

[SeasonLee]

bxbzg

You will notice the change and difference between the two stds when you make a comparison:
94 std : The position symbol is entered once and is applicable to both horizontal segments.
09 std : The position symbol is entered once and is applicable to all horizontal segments.

SeasonLee