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Assembly Drawings - Arrow tip for part callout on the outline of part 1

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renasis

renasis

Mechanical
Dec 29, 2002
56
Hello,

The arrow tip for a part callout on an assembly drawing should be coincident with the outline of the part, correct? This is recommended over the arrow tip pointing to the surface of a part, correct? Reference attached example of both methods. Is this specified in the ASNI Y14.5M standard, if so where?


Thanks,

renasis
 
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I couldn't find anything myself. But common since what say arrow should point to the part, that least i would do it. Interesting to see what other say.

Solid Edge V20
 
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This wouldn't be in 14.5 as it's not dimensioning as such. I can't recall if 14.24 says much.

If putting a leader to a surface rather than outline our CAD defaults to a 'dot' instead of arrow and I've seen this elsewhere, not sure it's in an industry standard and I don't have any of them to hand.

Coverage of assy drawings really is pretty sparse in the asme stds. 14.24 covers them and there's another which covers parts lists as I recall but I can't think of the number. Even 14.100 has a few relevant things. However, there really isn't that much on assy drawings all things considered.

KENAT,

Have you reminded yourself of faq731-376 recently, or taken a look at posting policies: What is Engineering anyway: faq1088-1484
 
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In all my areas of CAD work (electrical, civil, architectural) I have always used, and seen, a dot for a leader to a surface, as KENAT said. A dot will read "surface" and the arrow would read "this point on the surface", but I don't know if this in a standard anywhere.
 
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See ASME Y14.5M 1.7.4:

"...Normally a leader terminates in an arrowhead. However, where it is intended for a leader to refer to a surface by ending within the outline of that surface, the leader should terminate in a dot...

Marcelino Vigil
GDTP T-0377
CSWP
 
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Well what do you know, I was wrong about it not being in 14.5. Sorry. While it's probably not explicitly talking about balloons I'd be happy to read it across.

KENAT,

Have you reminded yourself of faq731-376 recently, or taken a look at posting policies: What is Engineering anyway: faq1088-1484
 
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Yes, I am aware that when referring to a surface that the leader should terminate with a dot.

I think that this thread is getting off track. What I am trying to determine is what standard specifies that the tip of the arrowhead should touch the outline of the part in an "assembly" drawing? Perhaps there is no standard for this?

 
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That seems to answer it. An arrowhead terminating in "space" is too ambiguous - was an item removed but the balloon left behind?. Termination with a dot removes that ambiguity, denoting the surface of an item as the termination.
Good luck finding that in the standards though.

"Good to know you got shoes to wear when you find the floor." - [small]Robert Hunter[/small]
 
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Thanks for all of the responses thus far. I guess my question gets more complicated with the introduction of hidden lines being used in an assembly drawing. Which I believe is allowed in the ASNI standard.

For instance, you have two parts which overlap in an assembly drawing. Lets say, a fan cover and a fan. The fan is drawn with hidden lines, while the cover is drawn with solid lines. If you were to use a leader that terminates with a dot(indicating surface) and that dot is coincident the fan and the fan cover, which part would you be referring to?

I would suspect the fan cover, but I could be wrong. If a leader arrow terminated on the outline of the fan cover and a leader arrow terminated on the hidden outline of the fan, there would be no ambiguity, as I see it.

So, my preference would be to use a leader with an arrow that terminates on the outline of the part, rather than using a leader with a dot that terminates somewhere on the part surface. However, I cannot find a standard to back up this claim. If anyone can find it, I would be interested in learning about it.




 
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You shouldn't be terminating to hidden lines. I would create a break-out on the cover to show a portion of the blade, then use an arrow termination on both cover and blade. If you didn't want to go through that trouble, and if it is not ambiguous, I would use a stacked balloon and only point to the cover. People will see the Part List and be able to determine what they need.

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

Have you read faq731-376 to make the best use of these Forums?
 
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I agree with MM. As in dimensioning, you should not point to hidden objects, but create a breakout. If there is no breakout, then the cover would be the item referenced.

"Good to know you got shoes to wear when you find the floor." - [small]Robert Hunter[/small]
 
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I'd be inclined to agree with MM & ewh. I don't think the standards are explicit about not ballooning to hidden detail (they really don't saty that much about assy drawings) but I would read across from ASME Y14.5M-1994 1.4g which says dimensions should be shown in true profile views and refer to visible outlines. If you use 14.41 things might get muckier but I still doubt ballooning to hidden line items is a good plan.

KENAT,

Have you reminded yourself of faq731-376 recently, or taken a look at posting policies: What is Engineering anyway: faq1088-1484
 
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Yes, I agree with MM, it would be better to have a breakout when identifying the part. I probably should not have used this as an example, because it is really not good practice to identify parts that are hidden on the assembly.

I believe my point/question keeps getting muddled with other arguments. My point, simply, is that it is better to have the part identification leader arrow point terminate on the outline of the part, rather than to have a dot on the surface of the part. I think there is less ambiguity when identifying the part this way.

 
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The closest you'll probably get to that is the "Normally" in vigildesigns quote above. To me this implies a preference for this technique.

KENAT,

Have you reminded yourself of faq731-376 recently, or taken a look at posting policies: What is Engineering anyway: faq1088-1484
 
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I think some of the reason that the argument is getting muddled is that you are looking for a standard saying one way is "better" than another. The standards don't really specify what is better, they way what is allowed and how to interpret drawings. They may imply a preferance in some cases, and as Kenat states, that's about the best you will find for a case that one way is better.

-- MechEng2005
 
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Renasis, I agree with your assessment that leader lines should only terminate to the solid object lines of components in an assembly drawing. About the only time I have ever seen the dot or "squiggly line" used in assembly drawings were when an area of a part was being referenced. One set of assembly drawings had an area that needed to be painted post-assembly, and it was this area that used the dot as an indicator instead of the outline of the area.

Wow, and if what I just wrote wasn't muddy enough...

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

Have you read faq731-376 to make the best use of these Forums?
 
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A lot of our parts fit very closely inside or are completely encapsulated by another part. In those cases pointing to the boundary with an arrow is unclear because two parts share the edge. That is when I use a filled dot or the squiggly line to a surface.

So is there any spec on the use of squiggly lines?
 
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