Basic Dim for Stock? 2

[MadMango]

Can a Stock dimension be Basic? I have a Schedule 40 pipe I need to define Run Out on, with the OD being A.

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[Belanger]

I would say yes, and here's why: In a sense, stock sizes are already assumed to be basic. (See the part in ASME about every dimension having a tolerance, and notice that stock sizes are exempt from that rule!)

But I'm not sure what you mean about applying runout to the pipe. The stock size -- even if toleranced -- wouldn't have any bearing on the runout.

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

 

[MadMango]

There is a machined feature on one end of the pipe, and I want to ensure it is not warped or bent prior to going into a weldment.

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[KENAT]

Belanger, can you remind me where in ASME Y14.5M-1994 that is, I couldn't find it the other day when I was looking.

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[MadMango]

In the 2009 standard it is 1.4 (a) Fundamental Rules.

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[KENAT]

Doh, thanks, I was looking in section 2.

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[Belanger]

Kenat -- Off the top of my head, I think it's the first one given in paragraph 1.4.

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

 

[DeanD3W]

I'm wondering why there is discussion of a basic dimension and runout... For a runout tolerance datum feature(s) used to establish an axis of rotation is/are needed and the surface with either circular or total runout applied needs to be identified.

Basic size dimensions are not needed to apply a runout tolerance, so I'm confused....??

Dean

http://www.d3w-engineering.com

 

[MadMango]

Perhaps I don't need the Runout. How do I ensure the pipe is not bent? Apply Straightness in two views?

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[pmarc]

Apply straigtness with cylindrical tolerance zone.

 

[MadMango]

pmarc, right...

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[flash3780]

I'm going to have to disagree with stock dimensions being basic. Stock dimensions are defined by standards. So, a proper drawing of a part using unmodified stock dimensions may use reference dimensions, not basic. Basic dimensions imply that the feature has a geometric control associated with it on the drawing. The guy machining/welding/brazing/etc the piece of stock has no control over the stock dimensions that he's working with - it's simply as bought.

I believe that ASME B36.10 covers steel pipe.

 

[flash3780]

I forgot to mention in my previous post - If I'm establishing a datum against an as-received surface, I do use a reference dimension and attach the datum to the leader line.

You can also put the datum flag directly on the surface (per Y14.5-1994, I haven't gotten the new spec yet), but I find it to be clearer to place it on the leader lines and give a reference dimension.

Also, be careful using MMC modifiers on datum references; stock tolerances can be fairly large, which can lead to a bit of datum shift. You need to be sure that it's taken into account in your stackups.

 

[prdave00]

I agree with flash3780. If I buy a tube of a certain gauge, there is still a size tolerance associated with the outer diameter. There may also be a straightness or other geometric tolerance. I typically put the "listed" dimension and tolerance on the print and place the word STOCK next to the call out.

The OD can still serve as a datum feature (also as flash3780 pointed out).

 

[MadMango]

Thanks to all.

"Art without engineering is dreaming; Engineering without art is calculating."

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