Component and assembly drawing drafting intent standard 5

[DaveJFT]

Hi folks,

I'm not sure if I've titled this thread correctly, but...

Is there a standard anywhere that states what the drafting intent should be for component and assembly drawings?

For instance, is there a standard that states whether a component or assembly drawing should be detailed (inc.GD&T) with a view to manufacture, inspection or purely to fully define the form of the finished item without consideration for how it will be manufactured or inspected?

The reason I ask is that when I'm detailing a drawing I come under pressure from both sides. Manufacturing engineers ask me to describe how the part is to be made. Quality engineers want me to dimension and tolerance the part how they would like to have it inspected.

Taking the latter case in point. I want to put total runout on a surface to ensure the whole surface conforms to my requirement but apparently that cannot be readily checked to the letter of total runout on the QE's preferred tool - a CMM, as it can only touch on points rather than scan the whole surface. Instead the QE's demand that simple runout be used on a set of defined diameters, or planes through a cylinder. However, this does not ensure my design intent is being achieved as no information is obtained from the surface between the planes. It could be as wibbly-wobbly as the face of a jelly baby, but we wouldn't know.

What I'm looking for is a clause in a standard that describes the intention of a component or assembly drawing to show to both parties that 'this' is he purpose of a component drawing and 'that' is how it has been detailed. Thus, if they each have further/different requirements then those should be described in a different manner.

Thanks for any advice,

Dave

 

[ewh]

Per ASME Y14.5, you define the part, not how to achieve it. There are exceptions when the method may affect some aspect of the part, but other than that, a drawing is not supposed to explain how to make the part, just what the part is. There should be separate manufacturing documentation to cover that.
That said, it is always a good idea to be aware of how the part is going to be made, as well as how it is going to be assembled. This may change how you approach your part definition.

“Know the rules well, so you can break them effectively.”
-Dalai Lama XIV

 

[KENAT]

Assuming you're in the US working to ASME stds then yest 14.5 would be the first place I checked. 1.4 is a good section for this kind of thing.

In ISO I'm not sure if it's as clearly stated. I believe the old BS308 said or implied this but now it's BS8888 I'm not so sure. Certainly some standards in the ISO system seem to lean more towards dimensioning for manufacturing.

Posting guidelines faq731-376

http://eng-tips.com/market.cfm?

(probably not aimed specifically at you)
What is Engineering anyway: faq1088-1484​

 

[pmarc]

Dave,
Just some excerpts from Y14.5 standard:
- Para. 1.4(d) - "Dimensions shall be selected to suit the function and mating relationship of a part..."
- Para. 1.4(e) - "The drawing should define a part without specifying manufacturing methods"
- Para 4.9 - "A datum feature is selected on the basis of its functional relationship to the toleranced feature and the requirements of the design"

There are some exceptions to these rules, but basically this is how parts should be dimensioned. Each other approach (that is satisfying manufacturing and/or inspections depts.) will most likely lead to a definition of requirements that in the end will not reflect how your part works in an assembly.

 

[Belanger]

And another rule from ASME paragraph 1.4:

"Dimensions and tolerances apply only at the drawing level where they are specified. A dimension for a given feature on one level of drawing (e.g., a detail drawing) is not mandatory for that feature at any other level (e.g., an assembly drawing)." para. 1.4(o)

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

http://www.gdtseminars.com

 

[TheTick]

Manufacturing engineers are very busy people. As such, they like to push work off to other departments whenever possible. Thus, it is common for manufacturing to try to push as much as possible back to design/drafting.

Another problem is "CAD myopia" (or "drawing myopia" for those still in the pre-digital age). This is the malformed idea that 100% of a part's information needs to be crammed onto a single drawing or in a single CAD file. This leads to all kinds of problems that could simply be solved with proper use of an MRP system.

 

[KENAT]

DaveJFT - if not in the USA working to ASME stds if you let us know what standards you work to someone may be able to point you in the right direction.

Posting guidelines faq731-376

http://eng-tips.com/market.cfm?

(probably not aimed specifically at you)
What is Engineering anyway: faq1088-1484​

 

[drawoh]

..."CAD myopia" (or "drawing myopia"...

Another problem is office politics. Manufacturing will seize control of the drawings if they can. This especially happens if engineering does a crappy job of documentation, or no job at all.

The OP should remind manufacturing that they understand the process. If the drafter tells them what to do, it is an insult.

--
JHG

 

[DaveJFT]

Hi All,

Thanks for all the replies. We're in the UK but working to ASME (as is becoming more and more common). Indeed, I'm working on one of the first drawings at our company to be done to ASME. Up until very recently it was BS 8888 - but no more. I missed the ASME training here earlier last year so I'm using my knowledge of ASME Y14.5M from my previous companies - anyhow I digress.

I'll use all the quotes from ASME Y14.5 above to defend my position that the drawing should fully define the part as is my design intent and ensure that the note specifying the drawing standard used is in place on the drawing - at least until the old BS standard drawings are obsoleted.

I've also seen elsewhere where it is stated that total runout (circular runout too) should not be measured on a CMM so I'll quote that too.

Cheers all!

Dave

 

[Belanger]

In the UK, ASME is becoming more common? Wow-- I keep hearing of more companies (even here in the US) that are adopting ISO. Interesting!

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

http://www.gdtseminars.com

 

[CheckerHater]

It may also be that OP’s company bought into sales pitch that ASME and ISO are the same.

More common than one may think: link

 

[Belanger]

Yes, the problem is that everyone's all eager to be "international," so they hear about ISO dimensioning/tolerancing and think that they must go that route. Ugh.

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

http://www.gdtseminars.com

 

[truckandbus]

I gave your initial post a star because I think

"It could be as wibbly-wobbly as the face of a jelly baby, but we wouldn't know."

is a brilliant description.