Does this print callout meet ASME Y14.5 1994

[Ron Rompen]

I have attached a copy of a print which I have received from a customer. Please note the location of Datum C, and the callout for the profile tolerance from Pt A to Pt B.

Is this in violation of ASME Y14.5(M)? I think that it is, but I'm not familiar enough with the standard to be completely sure.

Any opinions would be appreciated, as I have several more prints to review, all of which have the same type of callout.

(Never mind...can't attach the file for some reason. I'll have to figure out this problem first, and then try again).

 

[Wes Bucey]

I've put my copy of Y14.5 Dimensioning and tolerancing by my computer to answer a question.

The primary thing to determine is whether the dimension is understandable and thus buildable.

In terms of posting here, try taking a screen shot or converting the CAD to pdf.

Reality alert! I know a lot about GD&T, but I know enough to know I am NOT an expert. We may have to escalate the query.

My main question is why do you care whether the drafter has followed every convention of Y14.5? Is the drawing completely ambiguous and therefore unbuildable? In such a case, one simply goes back to each of the folks who signed off on the drawing and asks "precisely what do you mean?"

In my whole career, The only person I ever saw berate a drafter for not following GD&T was a drafting supervisor. Everyone else unable to understand the drawing did not bother to invoke GD&T, they simply asked for an explanation of the questionable section.

 

[Cari Spears]

Is the drawing completely ambiguous and therefore unbuildable? In such a case, one simply goes back to each of the folks who signed off on the drawing and asks "precisely what do you mean?"

In my whole career, The only person I ever saw berate a drafter for not following GD&T was a drafting supervisor. Everyone else unable to understand the drawing did not bother to invoke GD&T, they simply asked for an explanation of the questionable section.

I've seen some pretty silly things on drawings and have berated a drafter or two - but only to my own coworkers who were also trying to figure it out with me.

I agree - ask your customer what it means if it doesn't make sense. It means what the customer says it means regardless of what Y14.5 says.

 

[Jim Wynne]

Is the drawing completely ambiguous and therefore unbuildable? In such a case, one simply goes back to each of the folks who signed off on the drawing and asks "precisely what do you mean?"

In response, you’d likely get blank stares and incredulity at the idea that people who sign off on drawings are expected to understand what they’re signing off on. The reality of the matter is that drawings riddled with mistakes and ambiguities get approved all the time by people who have no clue what they’re signing off on. This doesn’t alter the fact that your premise—that questions need to be asked if the specifications are ambiguous--is certainly correct. The ones to ask are the designer and the CAD person (if they’re different people). I frequently find that the CAD person specified something that the designer didn’t intend, and neither of them are sure about how to frame the specification.

In my whole career, The only person I ever saw berate a drafter for not following GD&T was a drafting supervisor. Everyone else unable to understand the drawing did not bother to invoke GD&T, they simply asked for an explanation of the questionable section.

I’m not sure what you mean by “invoke GD&T.” The standard exists for good reason--to provide a uniform method for developing specifications that everyone can understand, and provide for a more precise method of designing the interface between mating parts. When the specifications are ambiguous, the system has failed, and correction is necessary. GD&T will often be used in ignorance, unfortunately, when there is no issue of mating or when the GD&T on one part doesn’t match up with the other. It’s not enough to just ask for an explanation. The intent needs to be documented, and if the drawing is indeed in error, it needs to be changed. This doesn’t mean that the world has to stop, but there should be a documentation system in place that allows for changes on the fly while the drawing is being updated.

A bit … Part of the problem lies in the fact that designers and/or CAD people are often loathe to admit that they’ve made a mistake, which leads to unnecessary delays while people argue back and forth. It’s a problem of expertise and authority. Every business that develops design drawings needs to have someone in authority who A) knows what he or she is doing, B) is reasonably objective, and C) has the unquestioned authority to make a decision when there is suspected error or ambiguity.

 

[Marc]

The reality of the matter is that drawings riddled with mistakes and ambiguities get approved all the time by people who have no clue what they’re signing off on.

Truer words were never spoken...

 

[Wes Bucey]

In the engineering environment I'm familiar with, there are usually 3 signatures on a drawing (apart from purchasing people who may be on the purchase order, but not on the drawing itself):

1. draftsman who executed the drawing (pen, T-square, compass, rule OR CAD)
2. drafting supervisor who is supposed to check the drawing for gross errors and adherence to the company "style"
3. design engineer who ensures the finished drawing meets his initial plan and requirements of the customer (internal or external)

In my business experience, each of those three is reasonably cognizant of GD&T and capable of catching a gross discrepancy in making callouts to datums which are impossible.

The most likely error I've come across since the wide introduction of CAD into the process is that the drafter will inadvertently leave the CAD software set at a default of three decimal places for tolerances when the design engineer only intended two decimal places for non-critical dimensions to save fabrication expense, thus EVERY dimension is listed at 3 decimal places (still buildable, but at extra expense.)

Sometimes engineers and draftspersons (many more females today than even 5 years ago) will go above and beyond GD&T by adding orthographic projections and isometric drawings or other 3D renderings to assure against ambiguous interpretations. (I've found this to be particularly helpful when dealing with some sheet metal fabrication shops in Europe.)

 

[bmccabe - 2006]

A bit … Part of the problem lies in the fact that designers and/or CAD people are often loathe to admit that they’ve made a mistake, which leads to unnecessary delays while people argue back and forth. It’s a problem of expertise and authority. Every business that develops design drawings needs to have someone in authority who A) knows what he or she is doing, B) is reasonably objective, and C) has the unquestioned authority to make a decision when there is suspected error or ambiguity.

You said it, JSW!

I've found this tack effective - Just say to the stonewalling cad jockey: "Look, Picasso: This product will never be static - Can't we just make the drawing easy to understand, and the part easy to manufacture? After all, your drawing is going to the shop floor, not the Louvre.


Ron, if you post the drawing, I’m sure I can make some sense of it.

 

[Wes Bucey]

Here's an example of two pages from my aerospace days when I made up a brochure for our engineers and purchasing folk to explain why we should go the extra mile in making drawings clear and unambiguous to our suppliers and installers.

Every engineer in our organization would have been able to sketch the 3 dimensional object just by looking at the 2 dimensional drawing on page 2, while no one in the purchasing department could come close. If our own purchasing department couldn't decipher the 2 dimensional drawing, we needed to be sure everyone at a fabricator could decipher it. Therefore, we added a 3 dimensional view to every drawing. Since our design engineers were already working in Solid Works, the extra view cost us nothing to produce and we found our turnaround time on quotations decreased nearly 50% with hardly any questions about interpreting the drawing compared with when requests for proposals and quotations only included 2 dimensional renderings.

 

[Jim Wynne]

Here's an example of two pages from my aerospace days when I made up a brochure for our engineers and purchasing folk to explain why we should go the extra mile in making drawings clear and unambiguous to our suppliers and installers.

Every engineer in our organization would have been able to sketch the 3 dimensional object just by looking at the 2 dimensional drawing on page 2, while no one in the purchasing department could come close. If our own purchasing department couldn't decipher the 2 dimensional drawing, we needed to be sure everyone at a fabricator could decipher it. Therefore, we added a 3 dimensional view to every drawing. Since our design engineers were already working in Solid Works, the extra view cost us nothing to produce and we found our turnaround time on quotations decreased nearly 50% with hardly any questions about interpreting the drawing compared with when requests for proposals and quotations only included 2 dimensional renderings.

That's a useful illustration, except for the fact that the 2D rendering on page 2 is in error; it doesn't show where the section is taken from, and the side view doesn't use phantom lines to make it clear that it's not a section view, if that was what was intended.

 

[Wes Bucey]

That's a useful illustration, except for the fact that the 2D rendering on page 2 is in error; it doesn't show where the section is taken from, and the side view doesn't use phantom lines to make it clear that it's not a section view, if that was what was intended.

You are correct. It was not a drawing to build a product. It was a drawing to illustrate a point about ambiguity. You'll note there are no dimensions in the 2D drawing, either. The task in the presentation mode was to ask folks to make a freehand 3D sketch of the product, no scale. Engineers took about 1 to 2 minutes, purchasing guys gave up after 15 minutes. It took me nearly 1/2 an hour when one of the engineers posed me with a different drawing, further illustrating why our turnaround time dropped so drastically in the quoting process. Even folks who had a clue what was wanted don't always easily grasp transition from 2D to 3D. Why not make it easy? After all, you want a finished product, not a contest to see who can interpret the drawing the fastest.