Drawing standards 2

[jdubya66]

I am going round and round with our Eng Mgr over our General Arrangement (GA) drawings. We build horizontal pumps that mounted on a skid, we dimension the location of the intake and discharge flanges, on our GA drawing, but we do not have a "tolerance block" in the tile block area of our drawing, and we do not have a +/- tolerance on the location dimensions. With that being said, our Eng Mgr tells me, since we do not have a "tolerance block", that all dimensions on the GA drawing are REFERENCE ONLY, but no where on the drawing do we state this. Is the Eng Mgr correct or not ??

 

[MikeHalloran]

If the drawing does not specify an external organization's standards for drawing interpretation, e.g. ASME or ISO or ???, then interpretation of the drawing is pretty much up to the beholder.

Your EM's interpretation is whatever (s)he wants it to be, but if there is no direct or indirect vector to a standard for interpretation, it becomes inevitable that a customer will disagree with your EM's interpretation, and that always turns out badly.




Mike Halloran
Pembroke Pines, FL, USA

 

[ewh]

I agree with Mike, and want to add that I think your EM is correct... untoleranced dimensions are "exact" as there is no tolerance range provided, and since there is no such thing as "perfect", they should be considered reference.

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

 

[LittleInch]

If I got a drawing with dimensions and no accuarcy block I would take it that that is exactly what I would get, emphasis on "exactly". Is your EM confusing "For reference" with "For information"?? For reference means you can refer to it no??

My motto: Learn something new every day

Also: There's usually a good reason why everyone does it that way

 

[1gibson]

Not very helpful to send a final GA that is usually considered "certified for construction" if it only includes "reference" dimensions.

What would you do with a warranty claim for nozzles that were 1/4" off from the drawing? 1/2"? 1"? Customer's problem? How would you fight a backcharge if piping was fabricated per your GA and customer had to rework once the unit arrived? You can't exactly say it is "close enough" if in fact, it isn't. Using ambiguity as a defense will only work one time per customer, if it works at all. Not a very good plan.

Ask a lawyer if 12.0" means 12.0", or 12.25".

 

[ewh]

A GA is a "general" arrangement; the only hard dimensions generally used are those to locate or install the assembly.
The reference dimensions are (or should be) derived from other drawings along with their applicable tolerances.

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

 

[BigInch]

Tolerance is only required for fabrication drawings.

Independent events are seldomly independent.

 

[Gator]

0.0625" for design, 0.125" for fabrication. It's always a joke when I see auto-generated isos calling-out 89.95 degree elbows in the Bill of Materials for sloped lines.

Paul
calgary.spedweb.com



Piping Design Central

http://www.pipingdesign.com

<a href="

http://www.gulfpub.com/product.asp?PositionID=campaign&ProductID=10679">The

Planning Guide to Piping Design</a>

 

[BigInch]

I see that, but ... not autogenerated.
Reminds me of the kind of engineer that always writes numbers to an accuracy of 5 significant digits, the first one wrong.

Independent events are seldomly independent.