Combining +/- tolerance & basic dimension to locate a hole.
Combining +/- tolerance & basic dimension to locate a hole.
(OP)
Hi All,
One more basic question. Please see the attached drawing.
Only one face of the block is mates with its counter part (datum feature B). the other side is open and does not mates with any surafces. The hole needs to be located with closer tolerances with respect to datum faeture B, the location of the hole from the other free face which can have a wider tolerance. In such case can we combine the +/- tolerance and basic dimensions to locate the hole.
Is it a legal specification in ASME? I have seen few drawings of this kind.
One more basic question. Please see the attached drawing.
Only one face of the block is mates with its counter part (datum feature B). the other side is open and does not mates with any surafces. The hole needs to be located with closer tolerances with respect to datum faeture B, the location of the hole from the other free face which can have a wider tolerance. In such case can we combine the +/- tolerance and basic dimensions to locate the hole.
Is it a legal specification in ASME? I have seen few drawings of this kind.





RE: Combining +/- tolerance & basic dimension to locate a hole.
ASME Y14.5-2009 para. 7.2.1.1:
"Dimensions used to locate true position shall be basic and defined in accordance with para.2.1.1.2"
One of the very few places where standard actually sais "shall"
I hope this helped.
RE: Combining +/- tolerance & basic dimension to locate a hole.
John-Paul Belanger
Certified Sr. GD&T Professional
Geometric Learning Systems
RE: Combining +/- tolerance & basic dimension to locate a hole.
I once saw someone clean a part by boiling it in gasoline on a kitchen stove. I wouldn't advise anyone else to do it.
RE: Combining +/- tolerance & basic dimension to locate a hole.
Belanger,
Per ASME Y14.5-2009 para. 7.2:
"Position is the location of one or more features of size relative to one another or to one or more datums."
The way I see it, if it is not located to the datum (or another feature of size), then it's not a "positon".
Your opinion?
RE: Combining +/- tolerance & basic dimension to locate a hole.
John-Paul Belanger
Certified Sr. GD&T Professional
Geometric Learning Systems
RE: Combining +/- tolerance & basic dimension to locate a hole.
And the "legal" definition of what it means is given where? How is the hole center to be related to the surface, all points, one point?
Frank
RE: Combining +/- tolerance & basic dimension to locate a hole.
This is actually very interesting.
I am a big fan of mixing GD&T with +/- dimensions myself, but this particular example looks like the worst way of doing it.
The question is "how to measure / gauge it?" Let say dim 50 is taken from "implied" datum. Is implied datum secondary or tertiary? How the resulting tolerance zone looks like?
I am really interested in seeing more opinions on this topic.
RE: Combining +/- tolerance & basic dimension to locate a hole.
I should add that the FCF probably shouldn't be pointing to the hole with the leader at an arbitrary angle. Better to show it with dimension/extension lines, similar to Fig. 7-28 of the standard, which are more clear about the direction of control.
John-Paul Belanger
Certified Sr. GD&T Professional
Geometric Learning Systems
RE: Combining +/- tolerance & basic dimension to locate a hole.
+/- dimensions are point-to-point. From what point on the left surface do you measure, and how do you establish the center of the hole horizontally?
Jim Sykes, P.Eng, GDTP-S
Profile Services www.profileservices.ca
TecEase, Inc. www.tec-ease.com
RE: Combining +/- tolerance & basic dimension to locate a hole.
John-Paul Belanger
Certified Sr. GD&T Professional
Geometric Learning Systems
RE: Combining +/- tolerance & basic dimension to locate a hole.
Why not to add tertiary datum feature C, then use basic 20 and 50 dimensions and assign bi-directional position callouts with 0.2 value in y direction and 1.0 in x direction? Would it create something confusing? Would it make measurements more difficult?
RE: Combining +/- tolerance & basic dimension to locate a hole.
Drstrole
GDTP - Senior Level
RE: Combining +/- tolerance & basic dimension to locate a hole.
Thanks, I think you covered the point I was trying to get at.
Frank
RE: Combining +/- tolerance & basic dimension to locate a hole.
Your drawing almost makes sense to me.
If a feature is controlled by two tolerance, both tolerances must be met. Your positional tolerance requires your hole to be within 0.1mm of true position. Anything that meets this, meets to ±0.5mm from the side.
Your drawing actually would make sense to me if you called up a sloppy positional tolerance, and then called up an accurate ± dimension on the 20mm dimension.
You can do this directly with GD&T, and leave the ± tolerance out. How about a composite tolerance frame in which your positional tolerances to datums ABC was Ø1mm, with a second frame from datum AB, calling up 0.2?
RE: Combining +/- tolerance & basic dimension to locate a hole.
Composite positional tolerance makes no sense unless there are two or more FOS. See 7.5 and 7.5.1 of Y14.5-2009.
RE: Combining +/- tolerance & basic dimension to locate a hole.
Why not?
I am not trying to do the same thing as section 7.5. I am trying to create a rectangular (not square) tolerance zone, as opposed to the normal round zone.
I could apply ± tolerances to each coordinate to the hole. On a simple part, this would work. On a complex part, with several features controlled by the dimension line, it would be hopeless.
RE: Combining +/- tolerance & basic dimension to locate a hole.
RE: Combining +/- tolerance & basic dimension to locate a hole.
If you were trying to create rectangular tolerance zone look at fig. 7-28 in Y14.5-2009 or 5-41 in Y14.5M-1994 standard for clear example.
RE: Combining +/- tolerance & basic dimension to locate a hole.
Let say, operative word is "one or more datums", so as soon as we have just one datum the FCF becomes legit.
Please look at the picture.
In "A" case we only relate to one datum [A]. "Position" in this case will become Perpendicularity. We all agree that +/- tolerances will be ambiguous, but if they are larger than hypothetical "shop accuracy" we will probably get the good part (from hypothetical shop
In "B" case we have some weird desire to control position in 2 directions separately and only use 2 datums for each direction. The picture looks, say, questionable, but not totally illegal.
Any ideas - are those better or worse than layout suggested (or questioned?) by Madhu?
Don't get me wrong - I think we already have a good solution, but trying to explore the possibilities.
RE: Combining +/- tolerance & basic dimension to locate a hole.
The solution I previously posted is similar to the scheme which was widely accepted by automotive customers. It was usually applied to slot dimensions which could be allowed more tolerance in the length directin than the width direction. The key is that applying the FCF to a hole size dimension that has a directional inference.
RE: Combining +/- tolerance & basic dimension to locate a hole.
The second picture does not automatically imply what is desired. Though most people would know what you're getting at, the standard is clear on how to display position tolerances that are only meant for a specific direction.
John-Paul Belanger
Certified Sr. GD&T Professional
Geometric Learning Systems
RE: Combining +/- tolerance & basic dimension to locate a hole.
You stated that plus/minus tolerances for location are "illegal because Y14.5 clearly says that basic dimensions shall be used to define true position."
I don't quite agree with that statement. Maybe plus/minus is illegal for locating a hole (I might argue that illegal is too strong of a word), but it wouldn't be for that reason. Yes, basic dimensions define a true position, but the term "true position" goes hand-in-hand with the GD&T position symbol. IOW, that rule doesn't extend to the general desire of locating a hole on a part.
I think we all neeed to be careful of the implications of the two words "position" and "location."
If the standard said that basic dimensions shall be used to define a feature's location, then plus/minus tol on a location would be clearly forbidden.
John-Paul Belanger
Certified Sr. GD&T Professional
Geometric Learning Systems
RE: Combining +/- tolerance & basic dimension to locate a hole.
Using Position to single datum to indicate perpendicularity is perfectly fine in composite frames, so everybody knows what it means; see for example Fig. 7-38(c) in Y14.5-2009.
And TheTick, how could possibly second frame contribute "orientation" but not "direction"? Could you have one without another? Almost like "position" and "location".
RE: Combining +/- tolerance & basic dimension to locate a hole.
The lower frame of a composite zone does more than perpendicularity; it controls the hole-to-hole location (even though you don't see any datums explicitly referenced for that).
I agree that most people would get the idea, but rules is rules :)
John-Paul Belanger
Certified Sr. GD&T Professional
Geometric Learning Systems
RE: Combining +/- tolerance & basic dimension to locate a hole.
John-Paul Belanger
Certified Sr. GD&T Professional
Geometric Learning Systems
RE: Combining +/- tolerance & basic dimension to locate a hole.
I would propose a revision to your picture the first position callout to ABC with the larger gross location (to "C" so to speak) and a second separate position call out to AB (to "B" so to speak) wirh the tighter number. That I believe is also legal and does what you want.
Frank
RE: Combining +/- tolerance & basic dimension to locate a hole.
I will disagree with the other's and say I do not think what you have shown is a technical violation in any way.
Tick,
While not implying "directionality" the extent of framework control only exists to the extent the stated framework can actually extend control, the effect is the same.
RE: Combining +/- tolerance & basic dimension to locate a hole.
John-Paul Belanger
Certified Sr. GD&T Professional
Geometric Learning Systems
RE: Combining +/- tolerance & basic dimension to locate a hole.
I would certainly agree with you on the issue of not using Position to experess simple Perpendiculariy control. Just by its implication it makes someone expect more or think that they are missing someting that was intended to be implied when they would not be. The result is it tends to adds to confusion and not to clarity, violating the old KISS principle.
Frank
RE: Combining +/- tolerance & basic dimension to locate a hole.
I am not sure that I understand your remarks regarding one of my posts correctly, but that is the end of a hard week, so please forgive me if my answer makes no sense.
I do not think I ever used term "location" in any of my previous posts in this thread.
For me location is either position, symmetry or concentricity - at least this is how I understand fig. 3-1 in Y14.5-2009. Someone can say that runout and profile are indirect location controls and that is fine for me. But in this particular case - with this particular part geometry - I do not see anything applicable besides position. If you are trying to say that op's print is controlling hole's position in vertical direction and hole's location in horizontal direction, then I am asking what kind of location is he trying to control? Is there any specific standardized name for this geometrical characteristic?
RE: Combining +/- tolerance & basic dimension to locate a hole.
Whoops, Sorry, I guess I also agree with your position on the first of CH's examples. I do not agree on the second, particularly now that you are supporting the mixing of +/- and position as in the OP, we do not really know the design intent so can it be done, by the book, I have to say, yes.
Frank
RE: Combining +/- tolerance & basic dimension to locate a hole.
The OP's example never used ± dimensions in conjunction with a position tolerance, so I had to read into your question a little bit, and apparently went beyond what you really meant.
But I was saying that the rule you give doesn't apply to the OP because his position tolerance was held only to datums A and B, which already do have basic dimensions. So I presumed your statement was focusing on the location in the east/west direction. As it is, the OP's example doesn't violate any specific GD&T rule (other than a change needed for where the FCF is placed on the drawing).
Then you ask:
"If you are trying to say that op's print is controlling hole's position in vertical direction and hole's location in horizontal direction, then I am asking what kind of location is he trying to control? Is there any specific standardized name for this geometrical characteristic?"
My reply: Yes, I am saying that the print controls the position in vertical, and location in horizontal. There is no name for the geometric characteristic in the horizontal, simply because it's outside the realm of GD&T. So we must use the more generic term of location.
That said, I agree with everyone that ± should not be used for location! It's really for size, chamfer, and radius only. But we were getting down to what's "legal," not what's "wise."
John-Paul Belanger
Certified Sr. GD&T Professional
Geometric Learning Systems
RE: Combining +/- tolerance & basic dimension to locate a hole.
RE: Combining +/- tolerance & basic dimension to locate a hole.
Is any of you guys getting confused when approaching an airport?
Somehow you reminded me one of my favorite movie quotes:
Eddie: Okay, we gotta pick a road. Arrivals or departures? We're arriving, but then we're departing. Which one, Snake?
Snake: What do you think?
Big Trouble (2002)
Read the standard: Location is the common term for position, coaxiality, concentricity, symmetry.
Then Standard explains that location between FOS, or between FOS and other feature you pick as a datum, is called POSITION, OK?
You cannot have location along the X and position along the Y, like you cannot be arriving and departing at the same time.
Many times I asked myself to keep quiet on Mondays
RE: Combining +/- tolerance & basic dimension to locate a hole.
So if I choose to use ± to locate a hole (which is fraught with issues, I realize, but we're just dealing with the concept right now), I would discourage you from calling it a position tolerance. Anyone else agree?
John-Paul Belanger
Certified Sr. GD&T Professional
Geometric Learning Systems
RE: Combining +/- tolerance & basic dimension to locate a hole.
You cannot call it "True Position", but it's still a Position.
Vote?
RE: Combining +/- tolerance & basic dimension to locate a hole.
Again, there is nothing in the standard indicating how to find the center of a hole when a +/- location tolerance is used. Perhaps "illegal" is too strong a word, but "indefensible" surely applies here. That ISO makes this somewhat clearer (though still not outlawing it) is a step. In '03, Y14.41 indicated the appropriate uses for +/- tolerances, and location of a FOS was not one of them. It is unfortunate that the list was not carried forward into Y14.5'09. One of the issues with a consensus standard is that good and seemingly-obvious items are sometimes diluted or dropped completely to achieve at least temporary closure.
Jim Sykes, P.Eng, GDTP-S
Profile Services www.profileservices.ca
TecEase, Inc. www.tec-ease.com
RE: Combining +/- tolerance & basic dimension to locate a hole.
So, no basic dimension, no true position. Did I say differently?
RE: Combining +/- tolerance & basic dimension to locate a hole.
Jim Sykes, P.Eng, GDTP-S
Profile Services www.profileservices.ca
TecEase, Inc. www.tec-ease.com
RE: Combining +/- tolerance & basic dimension to locate a hole.
RE: Combining +/- tolerance & basic dimension to locate a hole.
(Jim, I ain't defending the +/- but merely saying that it's there.)
John-Paul Belanger
Certified Sr. GD&T Professional
Geometric Learning Systems
RE: Combining +/- tolerance & basic dimension to locate a hole.
Shouldn't the conclusion be short: do not use +/- dimensions just for your safety because it is ambiguous and someone can misinterpret it?
Location vs. position discussion is important but not the clue of op question here.
RE: Combining +/- tolerance & basic dimension to locate a hole.
John-Paul Belanger
Certified Sr. GD&T Professional
Geometric Learning Systems
RE: Combining +/- tolerance & basic dimension to locate a hole.
RE: Combining +/- tolerance & basic dimension to locate a hole.
RE: Combining +/- tolerance & basic dimension to locate a hole.
RE: Combining +/- tolerance & basic dimension to locate a hole.
Jim Sykes, P.Eng, GDTP-S
Profile Services www.profileservices.ca
TecEase, Inc. www.tec-ease.com
RE: Combining +/- tolerance & basic dimension to locate a hole.
Using those as design inputs, you can remove the positional tolerance altogether and locate the hole using toleranced dimensions to both the horizontal and vertical surfaces. Then put a Perpendicular control to Datum A.
It will accomplish the same thing with no ambiguity's.
RE: Combining +/- tolerance & basic dimension to locate a hole.
RE: Combining +/- tolerance & basic dimension to locate a hole.
For shim with irregular outline contour do you think geometrical tolerance was applied wrong?
RE: Combining +/- tolerance & basic dimension to locate a hole.
This is why -- despite my seeming to defend ± location in earlier posts -- I always discourage it.
John-Paul Belanger
Certified Sr. GD&T Professional
Geometric Learning Systems
RE: Combining +/- tolerance & basic dimension to locate a hole.
But when I represent design in drawing I try to proceed from function. In my sample important only relationship between holes and datum surface.
Dimensions from corner just find location one of them. It is why I mentioned what is a piece.
I have been discourage too sometimes with GD&T standards because some info with samples just pure extract to show possible solutions but do not specified for particular cases.
Anyway I always come back to listen expert and learn lessons :)
RE: Combining +/- tolerance & basic dimension to locate a hole.
John-Paul Belanger
Certified Sr. GD&T Professional
Geometric Learning Systems
RE: Combining +/- tolerance & basic dimension to locate a hole.
Jim Sykes, P.Eng, GDTP-S
Profile Services www.profileservices.ca
TecEase, Inc. www.tec-ease.com