Controlling depth of separate counterbore. Bottom surfaces act as surface for alignment

[Bux1986]

Hi,

Seeking for advise on how to control the depth of two separate counterbores bottom surface ( highlighted)?
The surfaces need to move together.
The bottom surfaces of counterbore need to be used as surfaces for alignment ( keep a plate horizontal).
Can I use CZ or continuous feature? Please advise

 

[greenimi]

Can I use CZ or continuous feature?

ASME or ISO?

 

[Bux1986]

ASME

 

[3DDave]

Use a composite profile tolerance, 2X, or one callout with two leaders.

The upper frame references whatever is the important surface as a datum feature to control the depth range and the lower frame also referencing that same datum feature controls the limits to their mutual offset while maintaining parallelism to it.

 

[greenimi]

3DDave,
Just a quick folow up: looks like you are saying that there is no need CF symbol, right?
Do you think that two leaders is able to create the pattern mechanism in ASME?

Per what I know (2018)-copy-paste

3.44 PATTERN
pattern: two or more features to which a position or profile geometric tolerance is applied and that are grouped by one of the following methods: nX, n COAXIAL HOLES, ALL
AROUND, ALL OVER, between A and B (A ↔ B), from A to B (A → B), n SURFACES, simultaneous requirements, or INDICATED, where n in these examples represents a number.


I am questioning your statement

.....or one callout with two leaders.

 

[Bux1986]

I have added the call out ( composite ) as in the attachment.

My concern with this is it will still allow the two bottom surfaces to have a height difference of 0.1in Max ( with +/-0.005 tolerance for 3 digits)

Is there any call out or way to minimize this height difference?

Thanks

 

[3DDave]

Sorry Grenimi, I could not hear you over SIMULTANEOUS REQUIREMENT.

However I see where the redundancy department of duplication committee shows this in figure 7-27 by not only explicitly defining which surfaces are to be toleranced by directing leaders to them, but also the number of leaders that are pointing to those surfaces.

So, you caught me and forced me to again point out another stupid dogmatic rule to be parroted by the copy-paste gang.

I would not use CF because that would FIX the location of the zone and therefore require the use of the DYNAMIC modifier, et al, because it would essentially create a single surface and a single surface cannot have a composite tolerance.

 

[3DDave]

Bux - don't change how the feature is displayed. Go back to the section and use the profile tolerance scheme I wrote up before and don't use the depth symbol when you want a feature control frame because that depth is no longer allowed in the latest version of the standard. Sure, they depict it, but DIRECT TOLERANCES on dimensions that locate surfaces are discouraged, and have been removed to Appendix I.

 

[Burunduk]

Sorry Grenimi, I could not hear you over SIMULTANEOUS REQUIREMENT

A simultaneous requirement does generate a pattern, but since it is stated that it does not apply to the lower segments of composite feature control frames*, the pattern should be indicated by another method, so that the callout is fully interpretable as intended.

*The intent was surely that there is no simultaneous requirement between lower segments of several different FCFs. But, the potential for confusion is nevertheless there.

 

[3DDave]

As there is only one feature control frame there is no possible confusion. Just dogmatic pile on.

 

[3DDave]

Oh - look at that: Figure 10-16, version 2018.

It's in the book - Dogma wins again.

 

[Burunduk]

The confusion that may be caused is about whether the simultaneous requirement concept as a pattern generation tool is even relevant to lower segments of composites or not, due to what the text in the body of the standard specifies in the definition of the simultaneous requirement in the datum references section.

In Figure 10-16, there is no doubt that the two planar surfaces are under a simultaneous requirement because the two are profiled with ref. to [A] and the FCF is not composite. It would even be the same if two separate FCFs were shown with the same requirement instead of the single FCF with two leaders.

 

[3DDave]

May be? Lots of things "may be." You don't get to back-drive the rules when an obvious extension of principles is allowed.

One tolerance applied to two surfaces simultaneously creates a pattern and is applied simultaneously.

Clearly the writers of the standard failed. Just like they failed to provide your single solution explanation.

 

[Burunduk]

When it may, probably it often does, or at best sooner or later it will.