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I think Alex will admit that he might have slipped in this case. I agree and acknowledge that it has to be in print. I pointed out that the Standard explains the purpose of additional datum references where it is discussing all 3 orientation tolerances. That is pretty clear to me. But...

Hey powerhound, I am with you. The most important thing is to clearly communicate to the reader (customer). There are a lot of tricky things you can say on a drawing that would baffle the best of them. This was an interesting thread. Attaboys to all who participated.

Attaboy, caseynick. One comment, though. If a hole is parallel to the primary datum feature and perpendicular to the secondary feature, I could see a secondary datum feature referenced in a parallelism callout in order to "stabilize" a cylindrical tolerance zone. But, like caseynick said,"It...

Hi All, This was an interesting thread. Having attended the Y14.5 meetings where this was discussed I found it interesting that you all had the identical discussion. The line about "Relation to more than one datum feature is specified to stabilize the tolerance zone in more than one...

Hi Ringster Thanks. But, it is just another example of simultaneous and separate requirements. When I heard someone say simultaneous requirements only applies when datums are modified at MMC, I took that example to the committee. As a result, the 2009 revision has a prettier version of that...

Paul, the default is stated in 4.5.12 of the 1994 standard. Where two or more features or patterns of features are located by basic dimensions related to common datum features referenced in the same order of precedence and at the same material condition, as applicable, they are considered a...

In the 1994 standard Position requires a datum reference except in the lower segment of a composite position tolerance. In the 2009 revision: "7.6.2.3 Coaxial Features Without Datum References. A coaxial relationship may be controlled by specifying a positional tolerance without datum...

First, DesignBiz, in addition to my standards work and the Prof next to my name I own and operate a small manufacturing business producing pneumatic clutch/brake units. So unlike many engineers, not only am I responsible for the design, I also work with suppliers and am responsible for solving...

Not to worry, Ringster. People often say that if a part is controlled by ± tolerances the mating part should be also. Just because one part is poorly defined doesn't mean that poorly definning the mating part will make it OK. The newer revisions allow us to better define our parts. If...

Regarding Ringsters comment on "doublespeak": It is unreasonable to believe that when a concept is introduced, all possible applications and extensions of that concept can be addressed. When composite tolerancing was first introduced, no thought was given to what it would mean to have...

Ringster is right that the standards stand alone. However, the standards do evolve. As each concept is introduced, the users find applications that were not anticipated by the developers of the Standard. GD&T is a language. And like any language, it is determined by usage. Otherwise we...

Well, as an active participant of Y14 standards since 1988 and a member of the Y14.5 committee since 1995 assigned to the datums section, yes, I have read para. 5.3.2.2 pg 85 numerous times. In all fairness, this was a confusing area of the Standard for a lot of folks. We have spent a lot of...

If DesignBiz or anyone else thinks the drawings do not have the same meaning, please explain how the gage would differ. The gage shown does, in fact, automatically provide the datum shift. If datum feture B is produced at its LMC size of 30.2 it could "shift" a total of 0.4 on the Ø29.8 gage...

Datum shift occurs between the datum feature and the simulator. In both cases the gage elements for B and C are made at their virtual conditions (maximum material boundaries per 2009). This will allow the part to "shift" on the Ø29.8 pin and inside the 100.7 width in order to allow the other...

Great discussion! Zero basic was implied in the 1994 standard. See Figs. 4.26.5.45.18, 5.23 and others. The Standard shows both ways. With or without "half" dimensions. Since they are basic, it doesn't matter. Even the 1982 Standard has examples. Old figures that have been carried over from...

Interesting thread! I believe the original question has been answered by MechNorth and others. The first example is legitimate. The second example has a couple of problems. However, putting the lower tolerance on top is not one of them. The lack of the diameter symbol in the FCF without...

ISO and ASME Y14.5 were getting closer together until about 2004 when a revised ISO 1101 came out. ISO is very metrology based, especially with regards to CMMs. They like to talk in terms of extracted features. Y14.5 focuses on design intent to assure that parts assemble and work. Y14.5...

I found it!! Under Tools, System Options, Display/Selection I had to uncheck the box for "Display notes flat to screen."

juergenwt brought up a good point regarding fits. Where the fit is size on size you can refer to the American National Standards for both metric and inch in: B4.1 Preferred Limits And Fits For Cylindrical Parts B4.2 Preferred Metric Limits And Fits B4.3 General Tolerances For Metric Dimensioned...

MMR and LMR in ISO have the same meaning as MMC and LMC in the ASME Y14.5M-1994 standard. There are many changes that have been made to the ISO standards lately. My observation is that the ISO standards are becoming very metrology based to make it easy for CMMs to inspect parts. The Y14.5...