True Position, I don't understand.

[[Er...]]

I don't understand this one. U E and F has the same direction. How can I achieve this? Normally I don't work with ASME.

I thought the lower tier controlled orientation of the pattern as a group. Like the example on page 133, Y14.5-2009.
But as I said, ASME is not my regular cup of tea..

Any one that have time to expand my mind on this one.

[[Cl...]]

Looks like a Pratt & Whitney drawing.

Primary - Datum -U- Spatial & Z origin.
Secondary - Datum -E- XY origin.
Tertiary - Datum -F- planar (clocking)

Composite position. The upper segment is controlling the location of the holes relative to UE&F.
Second segment is controlling the position of the two holes relative to each other. Get rid of the
0.20 to UE&F, I don't think it belongs?

[[De...]]

This is a kind of deceptive / tricky call out.

There is two callouts actually if you look closely, the top portion - the first two lines is composite true position, and as was already stated, the first line is location and second line refines the orientation of the pattern.

The third line has its own true position symbol and therefore is a second true position callout defining location and orientation but not including the tertiary datum.

So the first line is location and orientation of the pattern to U E F and requiring all features in the pattern to be in a 2.00 diameter tolerance zone based on their nominal positions. So no fitting required, just check all holes to U E F.

The second line is refining only the orientation of the pattern to a tighter tolerance of 0.2 while disregarding location. so basically the pattern may be best fit in all translations and no rotations and must meet the 0.2 tolerance.

The third line is location and orientation of the pattern to U E and requiring all features in the pattern to be in a 0.2 diameter tolerance zone based on their nominal positions. So no fitting required, just check all holes to U E.

[[Er...]]

It's the 2:nd tier I don't under stand. How can I control orientation to E while still using U. Or cant they use UF, and skip E. Is that why its still there?
If I can translate in the lower tier, but don't rotate because of F, what point does the second requirement add? There I'm free to rotate..

So the point of this is: The actual location of the pattern based on basic is not that important. (2mm)
But the pattern it self must be within 0,2 in both rotation and translation within it self. Is that correct?

[[Br...]]

Please sign in to view this quote.

You are Correct. The upper segment should be treated as you normally would a position tolerance. The lower one controls orientation only. The pattern is free to translate. The result is a cylindrical tolerance zone with a diameter of 2mm at the true position of each dowel hole, with a smaller tolerance zone with a diameter of 0.20 that is inside of the Ø2mm tolerence zone.

I'm not sure if that answers your question though. What do you mean by " U E and F has the same direction"? Datum feature U is the plane on the face of this part that the holes go through, Datum feature E is a bore are the center of the part, and Datum feature F is a hole about 30° to the left of center. These 3 Datum features fully constrain all 6 degrees of freedom in the upper segment of the composite FCF. In the lower segment, they only control the 3 degrees of rotation. 3 degrees of translation is unlocked.

One confusing thing i noticed is a note that says "SECOND & THIRD PLANES OF THE DATUM REFERENCE FRAME ESTABLISHED BY THE 12 DOWELS HOLE PATTERN DATUM S". This might be true on a separate DRF that references Datum S, but for this DRF, those planes should be clocked in a manner that passes through datum features F and E simultaneously.

[[De...]]

You are correct, in the second line Datum E is not functionally required, as Datum U already constrains the same two rotations that Datum E would. I believe the spec says something about Datum Features being listed in the same order in subsequent lines, perhaps the engineer determined that meant they needed to include Datum E in the subsequent line.

Either way, as you already noticed, it has no effect on the callout that I can see.

And on your second point, yes the pattern must be good to itself within the tightest tolerance specified in order to meet the simultaneous requirement that is automatically created when the callout was made as a pattern that is related to the same datum reference frame.

[[Br...]]

Please sign in to view this quote.

I think Derek has probably hit what you're confused about on the head here. Any repeated datum references in the lower segment have to be repeated in the same order of precedence. So Datum E does actually have an effect here. the combination of E and F together establish the final degree of rotation. F alone cannot constrain that degree of rotation.

[[Cl...]]

Derek, you stated;

The second line is refining only the orientation of the pattern to a tighter tolerance of 0.2 while disregarding location. so basically the pattern may be best fit in all translations and no rotations and must meet the 0.2 tolerance.

Why, if it states the exact same callout as the first line (other than the tolerance) should it be interpreted a meaning something different? I'm just trying to follow you.

[[Br...]]

Please sign in to view this quote.

Because its part of a composite Feature control frame. Notice the Position symbol covers the first and second segment. That's establishing a composite feature control frame.

[[De...]]

Clarke, yeah exactly what Brett said, when a true position or profile symbol spans multiple rows in a callout, it indicates a composite true position / profile and the first line controls location and orientation and subsequent lines only refine orientation of the pattern.

After reading what Brett wrote that second line using Datum E makes more sense to me now, in order to have Datum F control rotation it needs a center point to rotate around and datum E provides a nominal position for that rotation to come from.

[[Cl...]]

So, in Calypso would you just report the position 3 separate ways as called out?
You couldn't do this w/in a single position characteristic could you?

[[De...]]

As far as I know, there is no way you could do this as one characteristic. I would report three results for each hole. One result for each tier of the callout.

In order to simplify the programming, I would most likely make the hole a pattern so it would only require 3 actual characteristics but it would report a separate result for each of the holes in the pattern.

[[Cl...]]

Thanks guy's!

[[Er...]]

Thanks Derek and Brett, I understand the purpouse of E now.

But I still think it looks awful and weired 🙂

How ever, Brett, I wish I could share the other 36 pages if you think that note looks strange.. (brittish engeneering)

[[Er...]]

Hum, another question. Is there any practical difference between the initial callout and this one then?

[[Br...]]

Those are two separate position FCF's. The top one references |U|E|F| as before, the Lower one is only to |U|. So since U can only control the two degrees of rotation and one degree of translation, the pattern is free to spin/rotate and translate in the remaining degrees of freedom. Pay close attention to any position and profile datum reference frames that have the exact same datums referenced, in the same order, and with the same modifiers. These are subject to a simultaneous requirement. In other words, If you have more than one set of features called out with just that "U" datum reference like you have shown, they need to be inspected at the same time. So if you best fit that hole pattern to get the position, you need to check any other features with that same DRF in the same alignment.

[[An...]]

Please sign in to view this quote.

This does not really explain the context between the two (or three) frames!

[[De...]]

Perhaps I should have just said the third line is a standard true position callout and should be treated as such.

[[An...]]

Here some thoughts about tolerance zones.
See attached.

Composite_True_Position_1.pdf

[[Er...]]

I really appriciate your effort Andreas.

So what you say is that datum E and F in the lower tier has no practical purpouse for the function of the part?

[[An...]]

Please sign in to view this quote.

Datum E and F define the orientation of the translatory tolerance gage.
See attached.

Composite_True_Position_2.pdf

[[Er...]]

Aaah, crystal clear now. Thanks.