True Position and datum B

[[An...]]

See attached.

Pic_4-32.pdf

[[Aa...]]

Ah, yes, the translation modifier. That was never included in the 1994 standard because it was the default behavior in 1994. This is probably the biggest difference between 1994 and 2009. In 1994, datum feature simulators are constrained rotationally (but not translationally) to preceding datums. In 2009, they are constrained rotationally and translationally to preceding datums unless they are followed by this modifier, in which case, they are constrained only rotationally to preceding datums.

In this example, without the modifier, it would be basically the slot's position relative to the axis of A that set the clocking about the axis of A. With the modifier, it is the slot's orientation only that sets the clocking.

[[An...]]

BSC versus Triangle.
See attached.

Picture_4-32_d.pdf

[[Aa...]]

The [BSC] modifier and translation modifiers are not opposites. The translation modifier is about releasing the location of the datum feature simulator. The [BSC] modifier is about establishing the size of the datum feature simulator. ([BSC] is just like MMB, except that the size of the simulator is simply the basic size, rather than being a product of the MMC size and other applicable tolerances. So, in your second example, the datum feature simulator is fixed at the size of 9.52. (If it were MMB instead of [BSC], that would be 9.22.)

[[An...]]

There might be a certain contradiction to picture 4-31.

[[Aa...]]

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4-31 applies [BSC] to a plane, not to a feature of size, like the datum in your example. Correction to my last post:

The [BSC] modifier is about establishing the size of the datum feature simulator if it's a regular feature of size. Otherwise, [BSC] is about establishing where within the tolerance applied to that feature the simulator must lie.

The ASME standard considers position to be a characteristic of features of size only, not of planes.

[[An...]]

1.) Secondary alignment of a plane
2.) Secondary alignment of two points

My personal point of view.
Not sure if this is according the rules.

See attached.

Picture_4-32_e.pdf

[[Aa...]]

I'm not sure what you're illustrating, there. At first glance, it looks like the green hatched area is the datum feature simulator, but that would not make sense, since the actual slots would violate the simulator. Moreover, the center plane of the simulator is required to go through the primary datum, namely, the center of the OD.

[[An...]]

Pictures 3a and 4a added.
See attached.

Picture_4-32_f.pdf

[[Aa...]]

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What is your basis for this?

[[An...]]

For reasons of technical logic.
See attached.

Picture_4-32_g.pdf

[[Aa...]]

You seem to be stuck with the assumption that absent any modifier, datum B is mobile. This is incorrect. (See 4.5.2(c).)

My guess is this assumption is based on 4-31(a). But don't confuse progression with translation. Progression is the nature of RMB datum feature simulators, moving proportionally from the MMB of the datum feature toward the LMB of the datum feature to maximize contact with the feature. Translation is what is allowed when the translation modifier is applied (or when the 1994 standard is used). The MMB and LMB of the datum feature are allowed to translate relative to preceding datums. When a datum feature is a plane, such as 4-31, a description of the simulator progressing sounds a lot like the datum feature is translating.

The [BSC] modifier is does not override the nonexistant assumed translatability. It indicates that the datum feature simulator is a maximum material boundary, meaning the surface of the datum feature can't violate it and it does not progress from MMB toward LMB, but rather is fixed as described by basic dimensions.

[[Aa...]]

To elaborate more on progression vs. translation, for 4-32 (which I think we've beaten to death), without the translation modifier, the progression of simulator B will be halted by contact with 2 points on the surface of the feature, as it is fixed at 5mm from datum A. However, with the translation modifier, allowing the MMB and LMB to translate to something other than 5mm from datum A will allow the simulator to progress further until it is halted by 3 points on the surface of the feature, ending with a larger simulator. (Note that in both of these scenarios, the RMB simulator progresses.)

[[Aa...]]

The translation allowed by the modifier is in order to allow the simulator to progress to a mating envelope that is constrained only in orientation.

I don't find any prohibitions of combining the translation modifier with a material boundary modifier, but it generally does not make sense, since the translation is supposed to maximize the progression of the simulator, and in non-RMB situations, there is no progression.

[[An...]]

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Yes,indeed!

Unfortunately paragraph 4.5.2 (c) produces an all-too-common nearly meaningless contents
that isn't helpful in this situation.

I think that Pic 4-32 (b) is wrong and has to be corrected.

A triangular modifier is applicable:
DRF Plane;Cylinder;Cylinder
both cylinders are parallel
DRF Cylinder;Cylinder
both cylinders are parallel

A triangular modifier is not applicable:
DRF Cylinder;Slot

The slot,as a "Direction-Giver", ensures the full rotatory mobility
until it comes to a "three-point-touching-situation" at the
expanding datum B-simulator and the actual surfaces.


See attached.

Picture_4-32_k.pdf

[[Aa...]]

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An expanding (progressing) simulator for a slot that is fixed at 5mm from the center axis will stop progressing (and lock rotation) at 2 points of contact. Depending on the situation, those arresting points might be both on the same wall of the slot, or they might be near opposite ends of opposing walls (like in 4-32(a)). Either way, the simulator could not progress as far as it could with translatability.

[[Aa...]]

[[An...]]

Well,I think Pic 4-19 brings it on the point.

(E.o.T.)