GD & T question? Weak Definition??
GD & T question? Weak Definition??
(OP)
What is wrong with the following drawing view??
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GD & T question? Weak Definition??
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RE: GD & T question? Weak Definition??
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.
www.axymetrix.ca
RE: GD & T question? Weak Definition??
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
RE: GD & T question? Weak Definition??
The min dims would seem inadequate. Not seen positional tol applied to ext line. Extension lines should not be interrupted with the FCF.... and more.
RE: GD & T question? Weak Definition??
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"?
RE: GD & T question? Weak Definition??
You asked us to be picky!
I would ask for a better definition than "weak". Maybe he thinks your tolerances could be made tighter. Maybe you used the wrong colour ink.
JHG
RE: GD & T question? Weak Definition??
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.
RE: GD & T question? Weak Definition??
RE: GD & T question? Weak Definition??
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
RE: GD & T question? Weak Definition??
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).
RE: GD & T question? Weak Definition??
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RE: GD & T question? Weak Definition??
RE: GD & T question? Weak Definition??
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
RE: GD & T question? Weak Definition??
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.
www.axymetrix.ca
RE: GD & T question? Weak Definition??
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: Eng-Tips.com Forum Policies recently, or taken a look at posting policies: http://eng-tips.com/market.cfm?
RE: GD & T question? Weak Definition??
RE: GD & T question? Weak Definition??
RE: GD & T question? Weak Definition??
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
RE: GD & T question? Weak Definition??
The datum feature G has a FCF attached, improperly, to the extension line on the right side.
The addition of the centerline is in reference to the lates tip of the month on Tec-Ease. Have you seen it?
RE: GD & T question? Weak Definition??
RE: GD & T question? Weak Definition??
The Edge... there is no honest way to explain it because the only people who really know where it is are the ones who have gone over. - Hunter S. Thompson
RE: GD & T question? Weak Definition??
KENAT,
Have you reminded yourself of FAQ731-376: Eng-Tips.com Forum Policies recently, or taken a look at posting policies: http://eng-tips.com/market.cfm?
RE: GD & T question? Weak Definition??
I agree that the FCF is improperly attached, but your comment stated that datum G was referencing itself and I wasn't seeing that. I also don't see the correlation of the centerline comment and the latest tip of the tec-ease website.
Powerhound, GDTP T-0419
Production Manager
Inventor 2009
Mastercam X3
Smartcam 11.1
SSG, U.S. Army
Taji, Iraq OIF II
RE: GD & T question? Weak Definition??
To be quite honest, I did not see the need for the centerline in the Tip Of the Month. But somehow things like this get disseminated by some people and it becomes the way to do it.
The statement was intended to be thought provoking.
RE: GD & T question? Weak Definition??
This is a lot of guesswork, mostly to try and figure out why someone would have an opinion about the relative strength of a GD&T callout. I am a newbie to GD&T, and I have discovered that there are about a thousand and one different ways to call anything out.
Some people like positional tols, some like surface tols, if you know what you are doing, you can make just about anything say what you want.
To make matters worse, we here are all going to pick on different things to nitpick as well.
My advice, go back and ask the original critic why they say that it is weak and see if you agree. It is entirely possible that your drawing is fine and the other person is wrong. You are not doing yourself, the critic or your company any favors by not following up directly. There is no reason to be embarassed either, if the critic is unwilling to help you, find someone else there who will.
GD&T is NOT an exact science, more of an art form that will take years of practice to master.
If you need a good text on GD&T, I recently bought "Dimensioning and Tolerancing Handbook" by Paul Drake and I have found it to be a very good reference.
Good Luck
RE: GD & T question? Weak Definition??
They position tolerances are assuming we want everything symetrical. BUT the keying feature on the left side is non symetrical.
A centerline would have made the implicit locations a bit more explicit, but the keying feature would violate that.
RE: GD & T question? Weak Definition??
RE: GD & T question? Weak Definition??
I have no clue.
RE: GD & T question? Weak Definition??
The drawing looks symmetrical to me. I cannot come up with any interpretation other than that. A centreline would make it look a little more symmetrical, which does not change the fact that there are no other possible interpretations.
One asymmetric detail does not affect any of this.
Perhaps the carbon fibre centrelines could run from corner to corner, creating a truss!
JHG
RE: GD & T question? Weak Definition??
Thus, Datum G is the 16.05±0.05 feature, constrained by Datums D and E (another feature of size, indicated by the MMC symbol), and the centerline is what all the other features are positioned to in a 0.25 tolerance zone. The only symetrical relationships are those that are related to Datum G.
The little thingus/doohickey on the left isn't an issue.