Quantity callouts 1

[AMontembeault]

Hello, I was wondering if some of you all might be able to clairify or perhaps share some "best practices" with respect to calling out quantities on engineering drawings when it comes to features (lets say holes) in a pattern.

Here is the confusion: In the GD+T standard, sections 1.9.5 and 1.9.5.1, a numeric callout of quantity "May" be used to indicate the number of features to which that dimension is applied. My interpretation of that is if, for example, I had a square 4-hole pattern (lets say 100 mm spacing in both the horizontal and vertical, I could either dimension it as 100 x 100 (basic of course) or 2x 100 x 2x 100 (again, basic), and either is technically correct.

But suppose I had multiple patterns with holes of various sizes laying on the same line? What then? What should I do if I have a number of holes of differing sizes which I'd still like to control as a pattern?

(See attached crude and hastily drawn sketch for clarification of what I'm asking)

 

[2JL]

Hello

Good questions here! I will be really interested on what other people do in these situations.
I think what should be considered is not how many patterns you have but how many times the dimension is repeated.
Also when I have a serie of holes linked through centerlines as in you sketch, I do not usually add a multiplier.

2JL

 

[ewh]

If your holes are in line and connected by a centerline, no quantity is needed. As in your example, you are dimensioning the distance between centerlines and to add a quantity would "muddy" the drawing. Even if there were one hundred holes on that centerline, no quantity is required to locate the centerline.

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

 

[KENAT]

100 x 100 works if you are showing common center-lines

2x 100 x 2x 100 works if you don't show common center-lines (but it's obvious the features are inline and hence what the '100' applies to)

It doesn't matter if the holes or other features are not identical so long as it's clear they are inline and so the '2X' dimension applies to them.

Likewise if using center-lines you can just put '100' and it applies to every feature on that common center-line regardless of individual feature size.

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[AMontembeault]

If your holes are in line and connected by a centerline, no quantity is needed. As in your example, you are dimensioning the distance between centerlines and to add a quantity would "muddy" the drawing. Even if there were one hundred holes on that centerline, no quantity is required to locate the centerline.

See, thats part of our confusion. Our design drafting department has been told numerous times from at least 2 different GD+T trainers/traning organizations that centerlines "Don't mean anything" - yet the standard itself does exactly what you propose. So do we trust the trainers, both of which are or have been on the GD+T committee, or do we trust the standard, understanding that the callout is optional? Are there times when it really shouldn't be optional?

 

[KENAT]

Center-lines by them selves do nothing (2.7.3 of ASME Y14.5M-1994).

Center-lines in association with a position (or maybe surface profile) tolerance on the features of size that share that center-line (hence saying how far you can deviate from that center-line) does have meaning*.

I would say combining 2X with center-lines is confusing and shouldn't' be done at all - pick one or the other. Most illustrations in ASME Y14.5M-1994(for what they are worth) show center-lines but no '2X'. Quick flick & I didn't notice any that had 2X + center-lines.

[*There is also an option of a general note covering feature alignment but I don't want to muddy the waters here.]

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[KENAT]

By the way, many folks religiously show center-lines in the type of pattern you're talking about - even if it leads to a messy drawing with lots of crossing center-lines etc.

I tend to think a bit more about it and pick either center-lines or '2X' depending on which will give a clearer less cluttered drawing.

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[ewh]

I have never heard that centerlines "don't mean anything" and would tend to trust the actual standard more than interpretations that seem to defer from it.

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

 

[KENAT]

ewh, all I can think is that the instructors were really meaning that just showing features aligned on center-line doesn't imply any tolerance to their permissible deviation from that center-line hence I flagged 2.7.3.

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[CheckerHater]

Our design drafting department has been told numerous times from at least 2 different GD+T trainers/traning organizations that centerlines "Don't mean anything"

The only way to deal with the experts like that is to ask them to show, where exactly ASME Y14.5 book says that cenerlines don't mean anything

"For every expert there is an equal and opposite expert"
Arthur C. Clarke Profiles of the future

 

[Belanger]

Yes, I'll bet the point was that center lines don't imply any tolerance among the shared axes. But center lines do at least imply that the the axes are designed to be aligned.

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

 

[fsincox]

It would be helpful if they did clarify what to do for complex parts where the "inline" may not be as obvious.
I have said it here before that, do to the simplified examples in the standard, things like this get missed and it is a headache for those of us out in the real world doing real parts if they do not.
Frank

 

[tbuelna]

I might argue that it would be more correct to use solid dimension extension lines rather than dashed center lines to indicate alignment between the hole centers as shown. A center line implies an axis of rotational symmetry, while a dimension extension line implies location of a surface or point relative to some other surface or point. And if extended implies location of a coincident surface or point along that extension line or curve. The use of center lines between the axes of hole features as shown does not define an axis of symmetry. The straight/parallel dimension extension lines shown imply that adjacent hole centers should be located in relation to those lines. Using center lines between the other hole axes would not necessarily imply they must be located along those straight lines. Just that the center lines must pass thru the axes of the holes, regardless of whatever shape they might take.

 

[Belanger]

tbuelna -- a center line doesn't necessarily imply an axis of rotational geometry. It could also be a center plane. See the attached snapshot from the Y14.5 standard, showing a planar block type of part.
And I'm not sure what you mean by "solid dimension extension lines." There are dimension lines and extension lines. (I think you mean the latter?)

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

 

[ewh]

I have to disagree with using a solid extension line through the center of a hole. The purpose of a centerline is to denote an item(s) center with a dash... to use a solid line defeats that purpose, and you may as well not use a centerline at all using that logic.

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

 

[Gilmiril]

Not only should the 'extension' lines between the holes be center lines, but also the extension lines outside the part to the actual dimension should also be center lines. This is consistently shown in Y14.5-2009 in, for example, Figures 1-6, 1-8, 1-14, 1-23, 1-32, 1-49, 1-50, et al.

At my work, however, I've been unable to get people to follow that because default dimensions in ProE always use solid extension lines, so it would require extra work.