Fig. 4-42 and para. 4.20 ASME Y14.5-2009

[Sem_D220]

1. Fig 4-42: why are all the datum target areas symbols used with dashed radial lines? For datum A, I understand that it means that the designated areas are on the bottom (hidden) side of the hood. But what do the dashed lines mean for datum areas B1, B2, and C1?

2. Para. 4.20 - Restrained Condition ends with the specification: "In a restrained application, it is permissible to use as many datum targets as necessary to establish the datum features."
How is that different from free state condition?

 

[Belanger]

Question 1 -- It simply means that those target areas are also on the far side of the piece as viewed.

Question 2 -- In the free state condition, those "extra" datum targets might not be contacted -- it depends on how well the part is formed and how floppy it is. But in a restrained condition, the part will be forced to contact all targets, even if it distorts the part from its free-state shape.

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

 

[Sem_D220]

Thank you Belanger.

I got it now regarding Q2 - makes sense!

Just to make sure regarding Q1 - does it really mean that B1 is located near A1 even though it is presented visually near A4, and C1 is actually at the rear edge rather than the front edge where the dashed leader is directed to?
I was thinking in that direction too but somehow it seemed to me as a too confusing way to show things on a drawing. Especially given that it is all shown on an isometric view and thus the sides of the part where the leaders point are unambiguous, to begin with.

 

[greenimi]

does it really mean that B1 is located near A1 even though it is presented visually near A4, and C1 is actually at the rear edge rather than the front edge where the dashed leader is directed to?

No. I don't think means that.
Means it is not on the visible side, but on the back side. It is not on your palm, but on the back side of your palm hand, so to speak.....

 

[Sem_D220]

No. I don't think means that.
Means it is not on the visible side, but on the back side. It is not on your palm, but on the back side of your palm hand, so to speak.....

Do you mean that datum area B1 is on the same surface as A4, and C1 is on the same surface as A6?

 

[greenimi]

Do you mean that datum area B1 is on the same surface as A4, and C1 is on the same surface as A6?

No. That is not what I meant.
The surfaces for B1 and A4 are normal/ perpendicular to each other (or maybe basic oriented to each other with any angle shown basic)
The same for C1 and A6. These surfaces are basic angled apart.

 

[axym]

Sem D220,

For what it's worth, I find the use of dashed lines on the datum target symbols in Fig. 4-42 very confusing as well. The target areas appear (to me) to be plainly on the near side of the part, particularly the B and C targets. I would have expected a mixture of solid and dashed lines, as in Fig. 4-54.

Evan Janeshewski

Axymetrix Quality Engineering Inc.

http://www.axymetrix.ca

 

[greenimi]

In fig 4-42 I see a hood of a car with its edges bent down (maybe 90 degrees from the top surface) then on these bent surfaces some datum targets place on the inside of the hood (where the engine is sitting and where the mounting points or feature are to be assembled).

As far as fig 4-54, hmmm , I do not understand it. Period. Much too complex for my own understanding.

 

[Sem_D220]

I would have expected a mixture of solid and dashed lines, as in Fig. 4-54.

Same with me. I thought the car hood is shown as if it has some significant thickness and that the datum target areas B and C are on the end surfaces along the periphery.

greenimi, thank you for clarifying. That's an interesting interpretation. I would probably not come up on my own with the idea of the bent down edges. If that is really the intent, then it explains the dashed lines indeed.

 

[SeasonLee]

As far as fig 4-54, hmmm , I do not understand it.

Glad to know I am not the only one lost here.

As for the fig 4-54, may I ask what's that means of basic dimension between datum targets A3 and B2? Is that means the thickness of the sheet metal?

Season

 

[Sem_D220]

As for the fig 4-54, may I ask what's that means of basic dimension between datum targets A3 and B2? Is that means the thickness of the sheet metal?

The basic dimension between A3 and B2 represents the height from the X axis (which passes through C1 and A3) to the B2 datum target line, that is supposed to be touching on the top end of the part.

 

[SeasonLee]

Ohhh,got it, I need to read it carefully.

Season