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GD & T question? Weak Definition??
- Thread starter ryandias
- Start date
I'm not sure what the intent is here, but I'll bite.
In this 2-dimensional view, it's difficult to tell what the features are that have position tolerances on them. Are we looking at bosses of different heights, or are there some gaps in there too?
The 6.40 +/- 0.15 dimension is a classic case of applying a plus/minus tolerance to a "non feature of size". Several features share the nominal 6.40 spacing, and some of them are non-opposed, so inspecting it would involve some guesswork and assumptions.
Evan Janeshewski
Axymetrix Quality Engineering Inc.
In this 2-dimensional view, it's difficult to tell what the features are that have position tolerances on them. Are we looking at bosses of different heights, or are there some gaps in there too?
The 6.40 +/- 0.15 dimension is a classic case of applying a plus/minus tolerance to a "non feature of size". Several features share the nominal 6.40 spacing, and some of them are non-opposed, so inspecting it would involve some guesswork and assumptions.
Evan Janeshewski
Axymetrix Quality Engineering Inc.
ryandias,
I assume that you have more information on the other views, so I am not willing to point out missing details. We cannot see where datums[ ]D and[ ]E are.
The 6.40 dimension looks like it should be 2X[ ]6.40.
The watermark looks like part of the word "CONFIDENTIAL".
Your object lines should be thicker than your dimension lines.
It looks like an electrical connector. Since we do not know what your requirements are, we cannot comment on the validity of your specifications. If datums[ ]D and[ ]E are properly called up, I can interpret your drawing.
JHG
I assume that you have more information on the other views, so I am not willing to point out missing details. We cannot see where datums[ ]D and[ ]E are.
The 6.40 dimension looks like it should be 2X[ ]6.40.
The watermark looks like part of the word "CONFIDENTIAL".
Your object lines should be thicker than your dimension lines.
It looks like an electrical connector. Since we do not know what your requirements are, we cannot comment on the validity of your specifications. If datums[ ]D and[ ]E are properly called up, I can interpret your drawing.
JHG
- Thread starter
- #5
Damn you guys are Picky!!
Thanks for the replies.
I should have given more direction to my question.
I was told that the GD&T position call-outs are "a weak definition."
Unfortunately I was a bit embarassed, that I didn't know what he was saying explicitly.
Now can anyone mention why he deems this use to be "weak"?
Thanks for the replies.
I should have given more direction to my question.
I was told that the GD&T position call-outs are "a weak definition."
Unfortunately I was a bit embarassed, that I didn't know what he was saying explicitly.
Now can anyone mention why he deems this use to be "weak"?
Where are "D" and "E"?
Maybe "soft" would be a better term than "weak". Probably some yutz wants to see actual dimensions explicitly locating the features. Giving benefit of doubt for what is not seen, it appears the features are adequately defined.
You can go ahead and post more of the drawing now. Your secrets are not that impressive or important.
Maybe "soft" would be a better term than "weak". Probably some yutz wants to see actual dimensions explicitly locating the features. Giving benefit of doubt for what is not seen, it appears the features are adequately defined.
You can go ahead and post more of the drawing now. Your secrets are not that impressive or important.
- Thread starter
- #8
ryandias,
Several of your prositional tolerances are tighter than your size tolerances. So what? There is nothing in ASME Y14.5M-1994 that says you cannot do this.
What are you trying to do? If your part is what I think it is, it must mate with another connector. The mating features have to clear each other. This is where I like to show nominal dimensions and zero positional error at MMC, although this is probably a bad idea for RP and any sort of casting or molding.
You should be trying to call up the loosest tolerances possible.
Do a tolerance stack up with the mating part, and see if there are any problems.
JHG
Several of your prositional tolerances are tighter than your size tolerances. So what? There is nothing in ASME Y14.5M-1994 that says you cannot do this.
What are you trying to do? If your part is what I think it is, it must mate with another connector. The mating features have to clear each other. This is where I like to show nominal dimensions and zero positional error at MMC, although this is probably a bad idea for RP and any sort of casting or molding.
You should be trying to call up the loosest tolerances possible.
Do a tolerance stack up with the mating part, and see if there are any problems.
JHG
- Thread starter
- #10
Drawoh.
You are correct it is a connector.
It is a connector companies design. I want no part in the design or responsiblity for its function. The views shown are direct "copies" of the vendor drawing. We have incorporated our own part with the connector spec'd from the customer.
The supplier is now ripping appart the sections that show the vendor drawing details. I am not sure of all the vendor drawing details, but have incorporated them as is (Neither I or my seniors want to undertake connector design responsibilities).
You are correct it is a connector.
It is a connector companies design. I want no part in the design or responsiblity for its function. The views shown are direct "copies" of the vendor drawing. We have incorporated our own part with the connector spec'd from the customer.
The supplier is now ripping appart the sections that show the vendor drawing details. I am not sure of all the vendor drawing details, but have incorporated them as is (Neither I or my seniors want to undertake connector design responsibilities).
I don't know where to start. I see a lot of problems... GD&T, drafting, etc.
Chris
SolidWorks/PDMWorks 08 3.1
AutoCAD 08
ctopher's home (updated Aug 5, 2008)
ctopher's blog
SolidWorks Legion
Chris
SolidWorks/PDMWorks 08 3.1
AutoCAD 08
ctopher's home (updated Aug 5, 2008)
ctopher's blog
SolidWorks Legion
powerhound
Mechanical
If datum D is the bottom or top surface of the connector and datum E is the OD (left to right), I don't think there is anything wrong with this in terms of how the features are dimensioned and toleranced but attaching the FCF to the extension line is not right and having the FCF cross over them is not right either as ringster said, but I don't think you were asking for a critique of your drafting technique. You were asking whether or not your dimensioning and tolerancing scheme was sound. In the absence of the rest of the drawing and making a few assumptions, I believe it is. There is nothing inherently wrong with having your positional tolerance looser than the feature tolerance unless it renders the part non-functional, but the practice itself is perfectly GD&T legal.
Evan,
I have a question; you mentioned the 6.40 dimension as being a classic example of a plus/minus tolerance on a "non feature of size" as if it were wrong to do. Is this what you meant or am I reading too much into your comment?
Powerhound, GDTP T-0419
Production Manager
Inventor 2009
Mastercam X3
Smartcam 11.1
SSG, U.S. Army
Taji, Iraq OIF II
Evan,
I have a question; you mentioned the 6.40 dimension as being a classic example of a plus/minus tolerance on a "non feature of size" as if it were wrong to do. Is this what you meant or am I reading too much into your comment?
Powerhound, GDTP T-0419
Production Manager
Inventor 2009
Mastercam X3
Smartcam 11.1
SSG, U.S. Army
Taji, Iraq OIF II
Powerhound,
You're not reading too much into it, I was trying to point it out as something that could be looked at as wrong. "Wrong" is a strong word, but it's an example that exposes the limitations of plus/minus tolerancing.
For example, consider the round-ended feature at the far left of the part. If I'm the inspector measuring the 6.40 dimension to the bottom end of this feature, how do I measure it? There is no directly opposing feature. I would have to line up on one (or more) of the 4 features that are nominally 6.40 away. If those features are not all exactly parallel to each other and in line with each other, there is more than one way to line up on them. The measurement could be done several ways, each with a different actual value. Getting the "correct" actual value, if there is one, depends on "tribal knowledge" of what the designer intended or what the part function requires.
Evan Janeshewski
Axymetrix Quality Engineering Inc.
You're not reading too much into it, I was trying to point it out as something that could be looked at as wrong. "Wrong" is a strong word, but it's an example that exposes the limitations of plus/minus tolerancing.
For example, consider the round-ended feature at the far left of the part. If I'm the inspector measuring the 6.40 dimension to the bottom end of this feature, how do I measure it? There is no directly opposing feature. I would have to line up on one (or more) of the 4 features that are nominally 6.40 away. If those features are not all exactly parallel to each other and in line with each other, there is more than one way to line up on them. The measurement could be done several ways, each with a different actual value. Getting the "correct" actual value, if there is one, depends on "tribal knowledge" of what the designer intended or what the part function requires.
Evan Janeshewski
Axymetrix Quality Engineering Inc.
One thought as to why they might consider it weak, you don't have a third datum in the FCF for orientation.
You say it's drawings of a vendor part if I understand correctly, in this case do you really need to show it, and if so unless it's a source control or something, should they all be reference dimensions?
I agree with a lot of the other comments about poor drafting practices etc, it's difficult to see the wood for the trees as it were.
KENAT,
Have you reminded yourself of faq731-376 recently, or taken a look at posting policies:
You say it's drawings of a vendor part if I understand correctly, in this case do you really need to show it, and if so unless it's a source control or something, should they all be reference dimensions?
I agree with a lot of the other comments about poor drafting practices etc, it's difficult to see the wood for the trees as it were.
KENAT,
Have you reminded yourself of faq731-376 recently, or taken a look at posting policies:
cedarbluffranch
Mechanical
I think the part that jumps out at me as being wrong is the fact that the word "confidential" appears on the drawing and this is a publically viewable form.
powerhound
Mechanical
ringster,
I don't think a centerline won't help at all. How do you think a centerline will help?
As far as relating G to itself, I don't see what you're seeing. Can you elaborate more?
KENAT,
If datum D is the top or bottom surface (which it probably is), and datum E is the outside of the part, relation to datum G provides orientation.
Evan,
Did you mean to use the obround feature as your example? It is certainly a FOS but you then referred to the 6.4 dimension which is used on something that is certainly not a FOS. Maybe now I'm not reading enough into what you're saying...
Powerhound, GDTP T-0419
Production Manager
Inventor 2009
Mastercam X3
Smartcam 11.1
SSG, U.S. Army
Taji, Iraq OIF II
I don't think a centerline won't help at all. How do you think a centerline will help?
As far as relating G to itself, I don't see what you're seeing. Can you elaborate more?
KENAT,
If datum D is the top or bottom surface (which it probably is), and datum E is the outside of the part, relation to datum G provides orientation.
Evan,
Did you mean to use the obround feature as your example? It is certainly a FOS but you then referred to the 6.4 dimension which is used on something that is certainly not a FOS. Maybe now I'm not reading enough into what you're saying...
Powerhound, GDTP T-0419
Production Manager
Inventor 2009
Mastercam X3
Smartcam 11.1
SSG, U.S. Army
Taji, Iraq OIF II
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