Non GD&T dimensioned features & assumed tolerances
Non GD&T dimensioned features & assumed tolerances
(OP)
We have several drawings that contain partial GD&T positional Tolerance. Most of the diametrical dimensions do not have any GD&T positional tolerance. The titleblock says the drawings are dimensioned and toleranced per ASME Y14.5-1994. There are also tolerances given for 2 and 3 place decimals (.03 & .010) and angular dimensions (+/- 1/2°)
My question is, what are the none GD&T dimensions held to positionally? See pic attached. Are they assumed located to a true center axes? What diameter do is used to find the center axes? Depending on the diameter you use, could it not change your inspection results? Are there assumed positional locations on these diameters or only size tolerances? Just a little confused as to what is assumed when there is no GD&T on a dimension.
Thanks,
John
My question is, what are the none GD&T dimensions held to positionally? See pic attached. Are they assumed located to a true center axes? What diameter do is used to find the center axes? Depending on the diameter you use, could it not change your inspection results? Are there assumed positional locations on these diameters or only size tolerances? Just a little confused as to what is assumed when there is no GD&T on a dimension.
Thanks,
John





RE: Non GD&T dimensioned features & assumed tolerances
Per ASME Y14.5M-1994 section 2.7.3 just showing diameters aligned by itself does not imply any relationship/invoke any tolerance.
Is there any not about assuming perfect form at MMC?
What is Engineering anyway: FAQ1088-1484: In layman terms, what is "engineering"?
RE: Non GD&T dimensioned features & assumed tolerances
RE: Non GD&T dimensioned features & assumed tolerances
That is correct. You will find a plethora of designers and engineers who insist that some sort of "industry standard" exists that restricts the positional location to the title block tolerance. This is not true. If the drawing invokes Y14.5M-1994 then one of the fundamental rules says that all tolerances must be stated.
Powerhound, GDTP T-0419
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Inventor 2010
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RE: Non GD&T dimensioned features & assumed tolerances
...I agree 100%; however, where in the standard is it stated that the tolerance block is not a valid statement? If it is not, what is its purpose?
I'm not saying that it wouldn't be much better to explicitly position the other diameter - far from it, just that, as poor as of a practice as it may be, the definition is still there and assumptions do not have to be made. I do not understand where "industry standards" enter into the question.
"Good to know you got shoes to wear when you find the floor." - Robert Hunter
RE: Non GD&T dimensioned features & assumed tolerances
Reading your response, my question would be: how many decimal places does implied 0 have? Which general tolerance - .03 or .010 controls the relation between cylinders?
RE: Non GD&T dimensioned features & assumed tolerances
pmarc pointed out exactly my rebuttal in those cases. The title block tolerances are based on decimal places and they are always "unless otherwise specified". In the case of these coaxial features, there are neither decimal places nor other specification.
Just assuming 2 or 3 decimal places is one assumption, assuming whether each cylinder should be coaxial to a single cylinder or whether each cylinder only needs to be coaxial to the one adjacent to it is another. There are plenty of assumptions to be made here.
Powerhound, GDTP T-0419
Engineering Technician
Inventor 2010
Mastercam X5
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RE: Non GD&T dimensioned features & assumed tolerances
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RE: Non GD&T dimensioned features & assumed tolerances
Thanks,
RE: Non GD&T dimensioned features & assumed tolerances
What's so difficult about concise, complete and unambiguous?
RE: Non GD&T dimensioned features & assumed tolerances
There is no clear answer to your questions, because the print you are showing is not clear, means it is ambiguous. If I had to measure a part shown on the print, I would be really confused what to do, except for the feature having positional tolerance applied.
First, I would not know if the coaxiality of other features is controlled relative to datum feature A or in a different way. Like powerhound mentioned, it is not precise whether each cylinder should be coaxial to a single datum feature cylinder or whether each cylinder only needs to be coaxial to the one adjacent to it. Having diameter dimensions on the print only is not clarifying the thing.
Second, even if we assume for a moment that coaxiality of all cylinders has to be controlled relative to datum feature A, it is not clear what controls the coaxiality - 1) general tolerance for linear dimensions (which, like I already described, is muddy enough for 0 dimension) or 2) general tolerance for angular dimension. These two can result in two different interpretations, so that makes things even worse.
I think the key to everything here is a word "assume". There are too many assumptions in this case. Even if I tell you that there is a positional relationship between features defined on your print, I cannot guarantee that my interpretaion would be the same as someone else's.
RE: Non GD&T dimensioned features & assumed tolerances
"Good to know you got shoes to wear when you find the floor." - Robert Hunter
RE: Non GD&T dimensioned features & assumed tolerances
Powerhound, GDTP T-0419
Engineering Technician
Inventor 2010
Mastercam X5
Smartcam 11.1
SSG, U.S. Army
Taji, Iraq OIF II
RE: Non GD&T dimensioned features & assumed tolerances
The answer is per my initial post and the section of 14.5 I refer to (assuming you're working to that standard).
Runz, yes without some explicit control or an all over note about assuming perfect form at MMC for aligned/coaxial ... features, there is no assumed tolerance for features shown aligned/centered. As such yes they could be infinitely misaligned and technically meat drawing requirements.
Runz, take a look at 2.7.3 of the standard rather than relying on all us talking heads
What is Engineering anyway: FAQ1088-1484: In layman terms, what is "engineering"?
RE: Non GD&T dimensioned features & assumed tolerances
What you are saying with 2.7.3 in Y14.5 is totally correct as long as there is absolutely nothing on the print that implies such relationship. Unfortunately there are those very muddy general tolerances on it and I think this is why Runz wants to know if they are defining mutual relationship or not.
My vote is that depending on who is reading the print the relationship can be interpreted differently. One can say there is a relationship, the other that there is nothing that controls the coaxiality. And this is sufficient to state that the print is ambiguous enough to be rejected.
By the way, if there were two features of size shown at right angle to each other without any geometric control, would you consider the general angular tolerance as a limitation of their mutual perpendicularity?
RE: Non GD&T dimensioned features & assumed tolerances
That is the point. I personally have never seen a print that has every coaxial feature with GD&T controls. The critical features have it, but the less important features do not. The only other dimensioning notes on these drawings are the default decimal and angular tolerances. Thus the reason for my question.
Thanks to all for their posts!
RE: Non GD&T dimensioned features & assumed tolerances
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RE: Non GD&T dimensioned features & assumed tolerances
Powerhound, GDTP T-0419
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Inventor 2010
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RE: Non GD&T dimensioned features & assumed tolerances
Even if you ignore that or think around it and want to invoke the block tols, if they vary with # of decimals how do you know which one to choose?
The OP states "ASME Y14.5M-1994" so I'm not sure why iso came up, or why there's much argument.
As to the 90° issue, this is addressed by 1.4(i) & (j)
Runz, just because it's common for aligned axis etc. not to be controlled, doesn't make it correct per 14.5. I've seen many drawings without such controls.
I believe there was actually a significant legal case relevant to this and I believe it may have been posted in an earlier thread about this topic. Basically a company sent out drawings without explicit controls on the coaxiality of some features. The machine shop was a ways off perfect alignment and the company rejected them. The machine shop took them to court, saying they met the drawing requirements, and the company was forced to pay.
The drawing is incomplete, ask for clarification from the design authority.
What is Engineering anyway: FAQ1088-1484: In layman terms, what is "engineering"?
RE: Non GD&T dimensioned features & assumed tolerances
So for that particular question of two FOS that are shown perpendicular to each other, yes we would go to the general angular tolerance in the title block. That's still not a great way to do perpendicular tolerancing, but I don't think it's ambiguous.
Coaxiality, however, isn't as simple because it's a linear relationship, not an angular relationship. So the number of decimal places comes into play -- we must throw up our hands and say it's an ambiguous drawing since there are no decimal places in the notion of center lines shown aligned with each other.
John-Paul Belanger
Certified Sr. GD&T Professional
Geometric Learning Systems
RE: Non GD&T dimensioned features & assumed tolerances
You said:
This was a point of my first response within this thread. You do not know which general linear tolerance to choose because you do not know how many decimals implied 0 has. But that does not mean the control is not there. There is still general angular tolerance which may be used by somebody to control the coaxiality.
Don't get me wrong. I do really believe the print is poorly dimensioned. I just want to reveal how many different interpretations may hide behind this scheme, which - by the way - I see very very often. Too often, I should say.
As to 90° - paras. 1.4 (i) and (j) tell that 90° angle applies but do not say what defines the tolerance for this angle. So my question is still the same: what would limit mutual perpendicularity of those two features if there was nothing specified in the print area besides limits of size and only general angular tolerance defined in the title block?
RE: Non GD&T dimensioned features & assumed tolerances
Fact is the OP's drawing is incomplete per the invoked standard.
What is Engineering anyway: FAQ1088-1484: In layman terms, what is "engineering"?
RE: Non GD&T dimensioned features & assumed tolerances
Pmarc ... since you posed the question, now I'm curious about your own answer!
John-Paul Belanger
Certified Sr. GD&T Professional
Geometric Learning Systems
RE: Non GD&T dimensioned features & assumed tolerances
I asked the question to Kenat hoping he would say that for two features shown at right angle on a print the general angular tolerance controls their mutual orientation. Having this answered I would then say that in my opinion general angular tolerance could be applied to nominally coaxial features as well, because the only difference is that the features are shown at 0° to each other and not 90°.
Personally I think general angular tolerance also causes troubles. It may be enough in some cases, but contains at least two shortcomings:
1. It is ambiguous since it is not known which feature to use as a base for angle measurement;
2. The tolerance zone is not fixed in width, which in fact can significantly affect functionality. The zone increases as it gets farther from the apex of the angle.
RE: Non GD&T dimensioned features & assumed tolerances
I always thought that the general tolerances apply to the dimensions (linear or angular) that are actually shown on the drawing, and not to dimensions that are not shown. If the general tolerance depends on the number of decimal places shown, then it has to work this way.
If a general angular tolerance applied to undimensioned angles, then it would control the angle between any two features on the part. This seems impractical - you could pick any two features and say that the angle between them must be within +/- 1 deg or whatever the general tolerance is.
What if the general tolerance for linear dimensions didn't depend on the number of decimal places, and was just a constant amount like +/- .030" or something? Would this apply to dimensions that are not shown on the drawing, or only to the ones that are shown? Again, it seems impractical for this tolerance to apply to dimensions that are not shown - then the distance between any two features would be subject to it.
I know we're not talking about ISO, but how do the general tolerances in the ISO 2768 standard apply? Do they just control dimensions that are explicitly shown on the drawing, or unspecified dimensions as well?
Evan Janeshewski
Axymetrix Quality Engineering Inc.
www.axymetrix.ca
RE: Non GD&T dimensioned features & assumed tolerances
As to iso2768 based on the standard I'd think only dimensions explicitly shown (at least part 1). However, my first encounter with that standard involved folks that thought otherwise.
What is Engineering anyway: FAQ1088-1484: In layman terms, what is "engineering"?
RE: Non GD&T dimensioned features & assumed tolerances
Pmarc, I see coaxial relationships as linear, so the general angular tolerance doesn't apply. General linear tolerances could apply, if we didn't have the issue of decimal places. The angular tolerance (usually) doesn't deal with decimal places.
John-Paul Belanger
Certified Sr. GD&T Professional
Geometric Learning Systems
RE: Non GD&T dimensioned features & assumed tolerances
To axym:
ISO 2768 Part1 is dealing with non-toleranced dimensions, Part2 is dealing with non-specified geometric relations, including circular Run-out. Coaxiality is not specified.
I like to refer to this picture:
http://www
It shows "invisible" GD&T implied by invoking 2768 very nicely.
RE: Non GD&T dimensioned features & assumed tolerances
1. Hole controlled by position callout suddenly interpreted as a datum feature C per main view of bottom sketch;
2. Perpendicularity callout 0.2 wrt C shown on the right view of bottom sketch. How somebody can even suppose that this tolerance must be considered relative to C and not to A for instance?
RE: Non GD&T dimensioned features & assumed tolerances
Powerhound, GDTP T-0419
Engineering Technician
Inventor 2010
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RE: Non GD&T dimensioned features & assumed tolerances
On the other hand, THERE IS view showing flats being perpendicular to axis of the hole, so perpendicularity is implied.
Good enough for me.
RE: Non GD&T dimensioned features & assumed tolerances
Frank
RE: Non GD&T dimensioned features & assumed tolerances
I see your point, however do not buy it. Would you really interpret it in this way if there were no dashed (general) tolerances shown? Look at a flat surface at the very left of the part. The interpretation is that circular runout 0.1 controls its relationship to datum feature B. My question is could not it be parallelism to A instead since both features are shown in the same view too?
powerhound,
Parallelism callout on the left view has datum reference. Notice that black triangle is attached to one of two faces which means this face is considered to be a datum feature. This way of FCF presentation was legal up till 2004 when new revision of ISO 1101 was issued. Since then it has been withdrawn. Unfortunately the picture we are talking about right now comes from ISO 2768-2:1989, so way before the method was clearly forbidden.
RE: Non GD&T dimensioned features & assumed tolerances
Nobody pointed out that there is a missing diameter symbol in the one position tolerance that does appear in the drawing the Runz referenced in his original post.
Just add a few more position tolerances and all would be well.
All good comments regarding how unwell we are if the ambiguity of "default tolerances" are allowed to exist.
Dean
www.d3w-engineering.com
RE: Non GD&T dimensioned features & assumed tolerances
Powerhound, GDTP T-0419
Engineering Technician
Inventor 2010
Mastercam X5
Smartcam 11.1
SSG, U.S. Army
Taji, Iraq OIF II
RE: Non GD&T dimensioned features & assumed tolerances
Powerhound, GDTP T-0419
Engineering Technician
Inventor 2010
Mastercam X5
Smartcam 11.1
SSG, U.S. Army
Taji, Iraq OIF II
RE: Non GD&T dimensioned features & assumed tolerances
Yes, I was also thinking about parallelism callout on the right view. Do not why I said it was on the left view.
RE: Non GD&T dimensioned features & assumed tolerances
RE: Non GD&T dimensioned features & assumed tolerances
Powerhound, GDTP T-0419
Engineering Technician
Inventor 2010
Mastercam X5
Smartcam 11.1
SSG, U.S. Army
Taji, Iraq OIF II
RE: Non GD&T dimensioned features & assumed tolerances
Powerhound, GDTP T-0419
Engineering Technician
Inventor 2010
Mastercam X5
Smartcam 11.1
SSG, U.S. Army
Taji, Iraq OIF II
RE: Non GD&T dimensioned features & assumed tolerances
Can you show us an updated drawing view that is more complete, based on this discussion and your own research into the design intent of the part? :)
Matt Lorono, CSWP
Product Definition Specialist, DS SolidWorks Corp
Personal sites:
Lorono's SolidWorks Resources & SolidWorks Legion