I have a question / Question from Don day GD&THierarchy Workbook
I have a question / Question from Don day GD&THierarchy Workbook
(OP)
Hello Gents
I am preparing for GDTP cert now.
so,I have been studying ASME standard and Don day's Hierachy workbook.
I have a question.
This question came from Hierachy workbook.
The GD&T Hierarchy Y14.5-2009 workbook.
The question number is C.5.6
(I have a solution note also..but there is no explain how to solve it)
Q : C.5.6
answer: a) 0.15
I only understand that hole is produced at 20mm (so, perpendicularity is increased to 0.4 mm / but actual out of perpendicular is 0.1mm-->??
Did I understand correctly?)
and Question : The pattern of features( 4 X ∅10 +/-0.2)may be displaced radially from the datum axis by
a : 0.15
Is anybody knows about this question?
Would you explain how to solve it?
Please help me.
I attached the captured photo of question.
Thanks
I am preparing for GDTP cert now.
so,I have been studying ASME standard and Don day's Hierachy workbook.
I have a question.
This question came from Hierachy workbook.
The GD&T Hierarchy Y14.5-2009 workbook.
The question number is C.5.6
(I have a solution note also..but there is no explain how to solve it)
Q : C.5.6
answer: a) 0.15
I only understand that hole is produced at 20mm (so, perpendicularity is increased to 0.4 mm / but actual out of perpendicular is 0.1mm-->??
Did I understand correctly?)
and Question : The pattern of features( 4 X ∅10 +/-0.2)may be displaced radially from the datum axis by
a : 0.15
Is anybody knows about this question?
Would you explain how to solve it?
Please help me.
I attached the captured photo of question.
Thanks





RE: I have a question / Question from Don day GD&THierarchy Workbook
this is about "datum feature displacement", or called "datum shift"
have a look at 5.3.2.2 in 1994 or 4.11.9 in 2009
in your example, you should consider virtual condition of datum feature B and its related actual mating envelope because it relates to datum A and is referenced as secondary datum.
virtual condition is ø19.6 and related actual mating envelope is ø19.9 so datum feature axis can be displaced in cylinder of ø0.3 (0.15 radially)
thus, your pattern of holes has additional position error allowed in relation to datum feature B axis.
RE: I have a question / Question from Don day GD&THierarchy Workbook
In order to know how much datum shift B is allowed for position control of pattern of 4 holes, it is not enough to know the size of the hole B. You must know the size of Related Actual Mating Envelope (RAME) of hole B - this is the envelope that is perfectly oriented and/or located with respect to preceding datum. So in this case you must know size of RAME that is perfectly perpendicular to datum plane A, because this is the only datum that precedes B in position FCF applied to 4 holes.
If the hole Ø 20 has no perpendicularity error the answer would be different. Because if it has any perpendicularity, the size of RAME of hole B will be smaller than Ø 20 and the amount of datum shift allowed will also become smaller.
20 - 0.1 = 19.9 (RAME)
19.8 (MMC) - 0.2 (perpendicularity) = 19.6 (VC at MMB)
19.9 - 19.6 = 0.3; 0.3 / 2 = 0.15
Same answer as Woosang.
RE: I have a question / Question from Don day GD&THierarchy Workbook
So, we take diameter 0.30 from FCF, divide it by 2 and get 0.15 The same result. Datum shift is NOT a bonus (according to Don)
"For every expert there is an equal and opposite expert"
Arthur C. Clarke Profiles of the future
RE: I have a question / Question from Don day GD&THierarchy Workbook
So you are not using in your calculation datum feature B “ ACTUAL” size (20mm)?
Also you are not using in your calculation the ACTUAL perpendicularity error (0.1mm)?
If not, why not? Does not matter? I am asking, please be gentle!
RE: I have a question / Question from Don day GD&THierarchy Workbook
Keep in mind that the current GDTP certification exams are based on ASME Y14.5M-1994. Also keep in mind that third-party textbooks paraphrase the content of the ASME standard, with different emphasis and wording.
Regarding question C.5.6, I would say that Woosang and greenimi's calculations are correct and capture the intent of the question.
But I also share CH's concern about the wording of the question in terms of how much "the pattern of features may be displaced radially from the datum axis". I would say that this wording is very misleading, and possibly incorrect. It should say "the datum feature may be displaced radially from the datum axis". This would follow what I believe the intent to be, which was to quantify the datum feature shift/displacement that greenimi described.
I happened to look at question C.5.5, and I believe that there is a problem there as well. The question uses the term "axis of datum feature B", which is defined as the axis of the unrelated actual mating envelope. In order for the axis of datum feature B to have zero deviation with respect to the four holes' basic location, it would have to be perfectly perpendicular to datum A. The thing that would have zero deviation with respect to the four holes' basic location is the axis of the related actual mating envelope of B (because B is the secondary datum feature, not the primary). Again, misleading and possibly incorrect.
Evan Janeshewski
Axymetrix Quality Engineering Inc.
www.axymetrix.ca
RE: I have a question / Question from Don day GD&THierarchy Workbook
Greenimi, there are several aspects to datum shift forming sort of a "murky" area that is not always considered or fully understood.
First, yes, datum shift is real. If you imagine the most simple situation, say bushing with OD serving as datum MMD and ID controlled MMC wrt said datum, the shift will even act as bonus allowing grater eccentricity.
BUT as soon as part becomes more complicated, it is easy to create the situation when part cannot even "shift" although the datum feature is actually "loose". Here comes the:
Second, no, datum shift is not bonus, you cannot simply add it to other tolerances.
Third: for practical reason it is safer to ignore datum shift, especially if you are using CMM. This is why authors of several books on GD&T recommend to be very careful around datum shift.
I doubt if simple straightforward solution will be found anytime soon.
"For every expert there is an equal and opposite expert"
Arthur C. Clarke Profiles of the future
RE: I have a question / Question from Don day GD&THierarchy Workbook
But can't fine such description in 2009-4.11.9 Datum Feature Shift/Displacement.
RE: I have a question / Question from Don day GD&THierarchy Workbook
I went back and read the wording from 5.3.2.2 (and 5.3.4.2), and I need to temper my comments a bit. In Don's defense, the wording in the questions is more consistent with the wording in the 1994 standard than I had thought. The standard does describe displacement in terms of the pattern of features being displaced (personally I find this confusing). However, the standard says that they are displaced relative to the datum feature's actual mating envelope. Question C.5.6 says that they are displaced relative to the datum axis, which I do not think is correct.
The description of datum feature shift/displacement was clarified in Y14.5-2009 Section 4.11.9. But in Section 7.3.6.2.2 Departure of Datum Features From MMB, some of the original description remains:
"In Fig. 7-18, illustration (b), where datum feature B departs from MMB, relative movement can occur between datum axis B and the axis of the related actual mating envelope of datum feature B. See para. 4.11.9."
Evan Janeshewski
Axymetrix Quality Engineering Inc.
www.axymetrix.ca
RE: I have a question / Question from Don day GD&THierarchy Workbook
I do agree (fully agreement) that:
1.) datum shift is real.
2.) datum shift is not bonus, you cannot simply add it to other tolerances
3.) for practical reason it is safer to ignore datum shift, especially if you are using CMM
But all the above 3 reasons DOES not prove that just take Ø.030 tolerance zone and divide it by 2 (in order to get the “correct” answer for the OP question) is valid. Again, I just go as far and say it is just flat wrong.
RE: I have a question / Question from Don day GD&THierarchy Workbook
John-Paul Belanger
Certified Sr. GD&T Professional
Geometric Learning Systems
RE: I have a question / Question from Don day GD&THierarchy Workbook
Would you mind to explain a bit why do you think your answer is the right one?
Just curious and confused about your replay from 2 days ago.
Thanks
Gabi
RE: I have a question / Question from Don day GD&THierarchy Workbook
Perpendicular to the tilt direction the pattern can move 0.2 + (20-19.9) = 0.4 diameter or 0.2 radially.
Since one typically wants to know the maximum displacement possible (minimum is always zero) the answer should be 0.2. If the question was rephrased as the displacement with the greatest limitation, that is 0.15.
I would also have worded it as the amount the A|B(M) datum reference frame can be shifted relative to the axis of the 20.0 hole. While more accurate describing the situation, I'm sure it doesn't parrot the words in the standard closely enough to be acceptable
Ignoring datum shift is a mistake. In many cases I have seen the greatest contribution to variation is due to bad datum selection leading to excessive shift. It might make inspection easier, but when the parts get installed the assemblers have to take time aligning unrelated features for workmanship.
RE: I have a question / Question from Don day GD&THierarchy Workbook
I'm not following you when you imply that the direction of tilt affects the answer. A datum simulator will be 19.6 in diameter. The 20mm hole tilted at 0.1 will result in a 19.9 inner boundary relative to datum A. You will only get 0.15 of radial displacement no matter how you move the part. In one direction, the datum simulator will hit the top of the hole and in another it will hit the bottom.
John Acosta, GDTP Senior Level
Manufacturing Engineering Tech
SSG, U.S. Army
Taji, Iraq OIF II
RE: I have a question / Question from Don day GD&THierarchy Workbook
I don't think my answer is the right one.
Huni said 0.15 is the right answer.
I was just saying that pattern displacement may have nothing to do with datum shift, hence radial displacement is the half of allowable diametrical displacement.
I didn't take bonus tolerance into consideration, but then it wouldn't be 0.15
"For every expert there is an equal and opposite expert"
Arthur C. Clarke Profiles of the future
RE: I have a question / Question from Don day GD&THierarchy Workbook
RE: I have a question / Question from Don day GD&THierarchy Workbook
Thank you for everyone
I'm reading every user's opinion carefully.
Thank you!
RE: I have a question / Question from Don day GD&THierarchy Workbook
RE: I have a question / Question from Don day GD&THierarchy Workbook
Hats off to Dave on this one. He's absolutely right, and to see it you have to go a couple of levels deeper. Forget what the standard says for a minute, and look at the geometry itself.
The picture that needs to be drawn is three-dimensional, with the tilted hole interacting with the datum feature simulator. The tilt brings the surface of the hole closer to the simulator surface and decreases the radial dispacement to 0.15 - but only in the direction of the tilt. In the "transverse" direction, the surface of the hole is not brought closer to the simulator surface and the amount of shift is still 0.20.
Evan Janeshewski
Axymetrix Quality Engineering Inc.
www.axymetrix.ca
RE: I have a question / Question from Don day GD&THierarchy Workbook
John Acosta, GDTP Senior Level
Manufacturing Engineering Tech
SSG, U.S. Army
Taji, Iraq OIF II
RE: I have a question / Question from Don day GD&THierarchy Workbook
"For every expert there is an equal and opposite expert"
Arthur C. Clarke Profiles of the future
RE: I have a question / Question from Don day GD&THierarchy Workbook
". Keep in mind that the writers of GD&T textbooks and exercise books (and even standards) can only get into the intricacies to a certain extent, without losing most of their audience"
I am lost!!
RE: I have a question / Question from Don day GD&THierarchy Workbook
"For every expert there is an equal and opposite expert"
Arthur C. Clarke Profiles of the future
RE: I have a question / Question from Don day GD&THierarchy Workbook
You're right, the tilt does bring the surface slightly closer in the transverse direction and reduces the displacement. No argument there.
greenimi,
I think I remember saying that in some other thread. The issue that Dave raised is one of those intricacies, that would lose 99% of GD&T people (committee members included). The MMB of datum feature B isn't really cylindrical - we only treat it as cylindrical because Y14.5 says it's cylindrical. The hole can be tilted in any direction, but it can only be tilted in one particular direction. Kind of an "or" versus "and" thing. So the datum feature shift has a directionality to it. But this is deeper than most people want to go.
Evan Janeshewski
Axymetrix Quality Engineering Inc.
www.axymetrix.ca
RE: I have a question / Question from Don day GD&THierarchy Workbook
Yes CH. I also have to hire a Certified Road Sign Professional
""""So far, in the world of GD&T, one has to hire Certified Road Sign Professional every time one takes car out for a spin."""""