Comments on: Position with Only One Datum? http://gdtseminars.com/blog/2010/05/18/position-with-only-one-datum/ Geometric Dimensioning & Tolerancing tips, questions and issues Sat, 19 May 2012 06:55:20 +0000 http://wordpress.org/?v=2.3.1 By: Steve Beals http://gdtseminars.com/blog/2010/05/18/position-with-only-one-datum/#comment-1113 Steve Beals Tue, 27 Mar 2012 17:11:19 +0000 http://gdtseminars.com/blog/2010/05/18/position-with-only-one-datum/#comment-1113 THANKS! But I have to add that I dont care if you refrence 15 datums, or a pattern. Say what you mean and mean what you say. Design engineers should use the orientation callout that makes proper sense for manufacturablility. In this and many cases : . PLEASE USE IT! or LEAVE IT OFF THE PRINT! Great article. THANKS!

But I have to add that I dont care if you refrence 15 datums, or a pattern. Say what you mean and mean what you say. Design engineers should use the orientation callout that makes proper sense for manufacturablility. In this and many cases : . PLEASE USE IT! or LEAVE IT OFF THE PRINT!

Great article.

]]> By: John-Paul Belanger http://gdtseminars.com/blog/2010/05/18/position-with-only-one-datum/#comment-1108 John-Paul Belanger Tue, 13 Mar 2012 18:20:05 +0000 http://gdtseminars.com/blog/2010/05/18/position-with-only-one-datum/#comment-1108 Hi Dave ... yes, you've nailed it. The standard calls the symbol itself "position." (I believe the symbol was at one time called "true position," but that's been several decades!) However, the term "true position" still has meaning. It is the theoretically perfect location that is desired. The "position" symbol then tells us how far from true position we may stray. It's not a huge deal, but yes, this is the idea that you were thinking of. Hi Dave … yes, you’ve nailed it. The standard calls the symbol itself “position.” (I believe the symbol was at one time called “true position,” but that’s been several decades!)

However, the term “true position” still has meaning. It is the theoretically perfect location that is desired. The “position” symbol then tells us how far from true position we may stray.
It’s not a huge deal, but yes, this is the idea that you were thinking of.

]]> By: Dave Zinn http://gdtseminars.com/blog/2010/05/18/position-with-only-one-datum/#comment-1104 Dave Zinn Thu, 16 Feb 2012 12:35:36 +0000 http://gdtseminars.com/blog/2010/05/18/position-with-only-one-datum/#comment-1104 A pet peeve of mine is when the (I think) uninformed refer to the position symbol as "true position." Am I correct in asserting that there is a concept of "true position" as mentioned in 14.5 and a "position symbol?" A pet peeve of mine is when the (I think) uninformed refer to the position symbol as “true position.” Am I correct in asserting that there is a concept of “true position” as mentioned in 14.5 and a “position symbol?”

]]> By: John-Paul Belanger http://gdtseminars.com/blog/2010/05/18/position-with-only-one-datum/#comment-1088 John-Paul Belanger Wed, 04 Jan 2012 05:10:36 +0000 http://gdtseminars.com/blog/2010/05/18/position-with-only-one-datum/#comment-1088 The only way to use position tolerancing with no datum references is if there are two or more holes involved in the same callout. Then I suppose it's possible: each hole simply becomes a datum for the other. The only example of this shown in the official GD&T standard is for coaxial (in-line) holes. In that case, they don't even need to be perpendicular to anything; the only thing desired is to keep them in line with each other. On your CMM, it wouldn't matter which hole you zero out on first. The only way to use position tolerancing with no datum references is if there are two or more holes involved in the same callout. Then I suppose it’s possible: each hole simply becomes a datum for the other. The only example of this shown in the official GD&T standard is for coaxial (in-line) holes. In that case, they don’t even need to be perpendicular to anything; the only thing desired is to keep them in line with each other. On your CMM, it wouldn’t matter which hole you zero out on first.

]]> By: Dale http://gdtseminars.com/blog/2010/05/18/position-with-only-one-datum/#comment-1087 Dale Tue, 03 Jan 2012 13:42:05 +0000 http://gdtseminars.com/blog/2010/05/18/position-with-only-one-datum/#comment-1087 I am relativly 'new' the the world of GD&T. I use a cnc controlled CMM and two different manual CMMs, with with cnc and manual CMMs having different software. I run into these type of things on print all the time and the people I report to can't understand why my software will not report the things being specified on the prints. By the way, how do you do true position of a hole with no datum specified? I am relativly ‘new’ the the world of GD&T. I use a cnc controlled CMM and two different manual CMMs, with with cnc and manual CMMs having different software. I run into these type of things on print all the time and the people I report to can’t understand why my software will not report the things being specified on the prints. By the way, how do you do true position of a hole with no datum specified?

]]> By: bjv http://gdtseminars.com/blog/2010/05/18/position-with-only-one-datum/#comment-786 bjv Tue, 27 Jul 2010 21:21:05 +0000 http://gdtseminars.com/blog/2010/05/18/position-with-only-one-datum/#comment-786 Finally!!!!! someone who knows what he's talking about when it comes to GD & T. I am so sick & tired of engineers using it incorrectly and then using their findings as the basis of rejecting parts. Finally!!!!! someone who knows what he’s talking about when it comes to GD & T. I am so sick & tired of engineers using it incorrectly and then using their findings as the basis of rejecting parts.

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