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GD & T question? Weak Definition??
- Thread starter ryandias
- Start date
Powerhound, orientation may have been the wrong word looking at it again, however there are only 2 datums specified in any of the FCF visible, which leaves one unconstrained degree of freedom.
KENAT,
Have you reminded yourself of faq731-376 recently, or taken a look at posting policies:
KENAT,
Have you reminded yourself of faq731-376 recently, or taken a look at posting policies:
powerhound
Mechanical
ringster,
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
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
Powerhound,
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.
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.
Ryandias
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
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
- Thread starter
- #26
After discussing with them during a meeting. My understanding of why he called it "weak" is that;
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.
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.
- Thread starter
- #28
ryandias,
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
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
Why there could be a centerline. By attaching a datum in-line with the dimension arrow it indicates that the feature is a datum (also, the fact that Datum G is accompanied by MMC in all the FCF). And that feature creates a datum plane at the center of the feature, represented on the drawing by a centerline.
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.
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.
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