Broken diameter dimension

[legrand01]

I'm having a discussion with a colleague regarding how to dimension a diameter that is broken into multiple segments. Imagine a cylinder that has slots machined down its length. Is it necessary to number the quantity of segments or is one diameter callout acceptable? i.e. do we need 3X Ø1.650 or can we just use Ø1.650?

 

[drawoh]

legrand01,

I do this sometimes. Move the diameter dimension off the feature. I know that SolidWorks will draw the radius line, making your drawing clearer. Using phantom lines to connect the diameter segments is even more clear.

How are you going to inspect this thing? Your calipers will not work. You will need a go-nogo gauge of some sort.

--
JHG

 

[legrand01]

We have a CMM. Inspecting isn't an issue. I am more concerned about calling it out "correctly".

 

[SeasonLee]

You may find out the answer at Fig.7-30 2009 Std (Ø64.6~Ø65.0).

Season

 

[Nescius]

Do you want it to be treated as one feature? The CF (continuous feature) symbol might be useful. Somebody on this forum posted an excerpt from the latest draft of Y14.5 that had a nice example. I'll try to find it...

 

[giggity]

Using the diameter dimension is fine.

 

[Nescius]

I couldn't find the thread, but I had a hard copy in my binder of GD&T resources...see attached for one way to do things.

 

[mkcski]

Pictorially you could "connect" the three areas by adding a circular extension between the surfaces and dimensioning to the extension circle. Although the standard does not define the extension line as "connecting" the three surfaces, the pictorial and dimensioning "imply" continuity.

Certified Sr. GD&T Professional

 

[pmarc]

Can I have a question or two?

Let's say that the cylinder in question has no interruptions. In other words, it is a regular feature of size. Assuming ASME Y14.5 is in charge, this means that two separate checks need to be performed:
1. Verification of actual local (two-point) sizes.
2. Verification of conformance to Rule #1.

Now, there is the cylinder with 3 interruptions, as shown in OP. According to Y14.5, what checks need to/can be performed in this case?

And finally, what requirement(s) on the OP drawing (regardless if 3X prefix is used or not) prevents the actual features in question from looking for example like this?

 

[Nescius]

Well, 2009 says this:

2.7.5 Limits of Size and Continuous Features of Size

The note “CONTINUOUS FEATURE” or continuous
feature symbol is used to identify a group of two or
more features of size where there is a requirement that
they be treated geometrically as a single feature of size.
When using the continuous feature symbol, extension
lines between the features may be shown or omitted;
however, extension lines by themselves do not indicate
a continuous feature. See Figs. 2-8 through 2-10.

Then, in figures 2-8 through 2-10, it's shown that rule #1 must be satisfied and that "each cross section shall be within the limits of size". The examples don't address what happens when there's no cross section to measure.

The excerpt from the new Y14.5 draft that I posted above does show a part with no opposing points, but a profile tolerance is used. I don't think CF is needed in this case. Coplanarity of independent planar surfaces can already be controlled without CF, as shown in Fig. 8-14 of 2009. I'd argue that coradiality (same center and same radius) of round surfaces could be controlled in the same manner. Even concentric round surfaces with different radii aren't a stretch; it would be analogous to the "stepped" planar surfaces shown in Fig. 8-16 of 2009. I suppose I'd argue that any number of independent surfaces, of any shape, could be controlled similarly as long as all the basic relationships are there, a sort of simultaneous profile requirement with no datum referenced.

Anyway, to answer some of your questions, pmarc: I think we can confirm Rule #1 in the same way that we'd confirm it for an uninterrupted cylinder. Regarding the size, I don't know. Y14.5.1M-1994 has an interesting way to define size, not a 2 point measurement, but sweeping balls through a part. I do not know the status of this document, though.

 

[pmarc]

Nescius,

Thank you for the aswer. I agree with you that Rule #1 could be confirmed, but would that be according to the letter of the current standard? Verification of Rule #1 is a must in case of regular features of sizes, but is the feature in question a regular feature of size?

Regarding the size verification (or actually the LMC size of the feature), per my knowledge Y14.5-2009 gives no information about how that kind of callout applied to that kind of a feature should be interpreted. In other words, the callout is subject to multiple interpretations.

In the draft of new standard the committee (finally) defined a method of interpreting size callout applied to regular feature of size with localized areas that do not contain opposed points (para. 5.7.1 and fig. 5-9), but this is good for a future, not for today.

 

[Nescius]

pmarc,

Could you post that passage and figure from the draft of the new standard? I don't have the draft, and I think that passage would be good "food for thought" in this thread.

Regarding Rule 1 and the cylinder with 3 interruptions: I agree that questioning if we "must" test for conformance is equally important to questioning if we "can" test for conformance. Even though I answered that, yes, I think we "can" test for conformance to Rule 1 in this case, I do not think the results are equivalent to a whole cylinder passing the same test. The interrupted shape can have poorer form while still fitting in a given envelope. So, what does passing the "test" actually mean? It would guarantee assemblability in "pin in a hole" situations, but is that all we rely on Rule 1 for?

 

[pmarc]

Nescius,

My apologies that it took me that long but here are two pics from the draft:

http://files.engineering.com/getfil...448a-bd24-d439c03fdf58&file=5_7_1_e_draft.PNG

http://files.engineering.com/getfil...819-4ccc-ab7b-096abb4b4462&file=5-9_draft.PNG

 

[Nescius]

Thanks, pmarc. So, according to the proposed draft, if a region is missing, the UAME takes its place for the purposes of a 2 point measurement.

 

[pmarc]

Correct, Nescius.

Without having this explicitly defined in the standard, I have been always wondering how people interpret that kind of callouts.

If I remember correctly even on this forum we had one or two discussions on that subject.