Is this a pattern rule or simultaneous rule 4

[sendithard]

Hope you all are doing well, happy new year.

I'm questioning my understanding on whether this is a rule for a pattern or simultaneous rule. Seen below is a bolt hole pattern, no bottom datum as this is a quick example. There is some datum shift with the A datum, I just forgot to put the symbol in the model.

Because this is a pattern, we know you get your datum shift once, meaning you cannot best fit each hole individually, the moment you find your best fit, the tolerance zones as a pattern must remain there based on the basic angle and basic bolt hole circle diam.

Is this a rule under 'simultaneous' or is this a pattern rule? I know it may not make a bit of difference, but I just want to be able to describe it correct. We have a program that is best fitting each hole independently and there was an issue today and they didn't agree with me that the holes get a one time shot at a best fit, not 5 independent best fits.

Thanks.

 

[3DDave]

Pattern. Simultaneous applies across multiple FCFs.

 

[Burunduk]

I would use the more general term pattern.
According to the Pattern definition in Y14.5-2018 -3.44, a Simultaneous Requirement is just one way out of several to invoke a pattern. Also, according to the Simultaneous Requirement definition- 7.19 "In a simultaneous requirement, there is no translation or rotation between the datum reference frames of the included geometric tolerances, thus creating a single pattern".

 

[sendithard]

Appreciate the quick replies fellas. I'm getting beat up a bit in the QC department lol

 

[3DDave]

It a shame when QC is either illiterate or looking for a fight. Worse when it is both.

 

[Ryan6338]

If this were interpreted under ISO, simultaneity is not default - a CZ modifier would be needed in the FCF to specify this.

Ryan.

 

[sendithard]

Ryan,

Is there anywhere I can read a copy of the ISO standard for free? We may have one at work, but I'm sure you cannot Ctrl-F and search for a term as most pdfs we have seem to almost be scanned pdfs. I'm at the point where I could handle the brain damage from reading some ISO stuff.

BTW, are you certain that a basically dimensioned pattern should not have tolerance zones adhering to the basic dimensions from the drawing in ISO land? Would someone making a drawing of a pattern of bolt holes that need tolerance zones set at origin at the basic locations to not be adhered to somehow if they missed typing in CZ on the drawing?

 

[Burunduk]

Sendithard,
If the holes were fully constrained by the datum simulators, they would be forced to be fixed relative to each other within their tolerance zones, with or without CZ. Since datum feature A doesn't constrain rotation about the datum axis, the holes could vary in rotation and without applicable definitions each hole could rotate differently. In ASME it is taken care of by the pattern creation rules, whereas in ISO patterns aren't created by stuff like "nX" and there is no Simultaneous Requirement default, patterns have to be explicitly stated by the CZ modifier.

 

[pmarc]

sendithard,
Just to be clear, there is no single ISO standard that defines everything. ISO GPS is a multi-document system. When it comes to patterns, you may want to take a look at ISO 5458:2018 and ISO 2692:2021 for tolerancing at MMC (they call it MMR).

Just keep in mind that per the previous version of 2692 from 2014, the presence of the MMC modifier was enough to impose angular relationship between the features within a group. This changed in 2021 so one needs to be careful which version of 2692 is in use.

PS. It is good to see that the number of people in this forum that offer valuable insights about ISO systematically increases.

 

[3DDave]

I would welcome the elimination of Y14.5 to be replaced entirely by ISO GPS. The Y14.5 standard is riddled with words that are redefined from normal use, sometimes nearly opposite the accepted definitions.

A pattern, anywhere else, is composed of repeated identical features, usually at a uniform spacing along one direction or two. "Pattern" is sometimes adapted to refer to the item that is responsible for making identical features, such as a sand casting pattern or a clothing pattern. Not so in Y14.5 where it can be any group of anything at all.

Close the door on the Y14.5 process that comes to such agreements and makes them standard.

 

[Ryan6338]

Sendithard,

See the attached snipped from sections 5.1 & 5.3 of ISO 5458:2018. Basic dimensions do not impose any tolerance inherently. Under Rule A from section 5.3, not defining SZ, CZ or CZR is invalid when using a position specification and there are unlocked degrees of freedom.

From 5.1

From 5.3

Ryan.

 

[pmarc]

I would welcome the elimination of Y14.5 to be replaced entirely by ISO GPS. The Y14.5 standard is riddled with words that are redefined from normal use, sometimes nearly opposite the accepted definitions.

A pattern, anywhere else, is composed of repeated identical features, usually at a uniform spacing along one direction or two. "Pattern" is sometimes adapted to refer to the item that is responsible for making identical features, such as a sand casting pattern or a clothing pattern. Not so in Y14.5 where it can be any group of anything at all.

Close the door on the Y14.5 process that comes to such agreements and makes them standard.

The Y14.5 committee has been aware about that for a while and they have been working on redesigning the standard to be rule-based as opposed to being example-based today.

Surprsingly, I don't think they have recently considered the elimination of Y14.5. ;-)

Also, I wouldn't say ISO uses "pattern" and "pattern specification" only in the context of identical features.

 

[3DDave]

Slaying one dragon at a time. The words "group" or "set" are used in the remainder of society for items that may not be identical but are related in some way.

There is, no doubt, some cross-contamination for consistency. Maybe that's where Y14.5 got that notion.

They appear to have gotten the toilet plunger from ISO along with the space-taking extensive leader that adds no clarity.

They certainly have a vast vocabulary for keeping the barrier to entry very high.

I do see they understand that numbering simultaneous requirement statements so that sub-groups can be made is part of the standard, though it doesn't appear to be required.

It is so much friction, when it should be simple - are surfaces being grouped as if a single feature or are tolerance zones being grouped as if from a single coordinate system?

Instead there is SIM and CZ which are essentially singular and plural indicators for the exact same thing, but wait, there's more. Still head scratching over how 50 holes with 50 separate tolerance zones can be considered to have a common zone when all they have in common is the coordinate system, but maybe it's different in Europe.

Anyway, other dragons, other days.

 

[sendithard]

Ryan,

Thanks for that snippit. I see those modifiers all the time in our software and I need to do a better job learning them. They could come in handy at some point.

pmarc,

Do you like iso better for some reason?

 

[pmarc]

sendithard,

It is not that I like ISO better than ASME - both systems have some pros and cons, as I mentioned in the parallel thread. In perfect world, it would be great to have a single standard that would somehow combine strong sides of both systems, but unfortunately it does not look like the merge is going to happen any time soon or at all.

 

[3DDave]

There are no technical reasons preventing a merge; they cover the same area and, presumably, everyone in this area has the same materials, machines, inspection equipment, and mathematical knowledge, and problems to manage; similarity to the extent that the two standards are not affected by any minor differences among individual companies.

There are political and economic reasons not to.

As long as the majority of industry barely cares about the results, there won't be any pressure to fix the oddities or make syntax checking and tolerance analysis software integral to the CAD system.

 

[greenimi]

There are political and economic reasons not to

I agree wholeheartedly with that.
Sometimes the scope of hegemony (and maybe imperialism) spills over into other areas than they originally were designed and intended for.

 

[pmarc]

Political and economic reasons play important / main role, but there are also some underlying technical reasons why these two groups don't play the same game. For example, in the merged standard they would have to find a consensus on topics like: default independency or Rule #1, default independency of specifications or simultaneity, default size interpretation, etc.

Long story short, I am afraid the division has already gone too far to now be able to do a reasonable unification.

 

[greenimi]

pmarc,
I am not really sure which one was first, but I am afraid that this drift apart (between ISO and GD&T) came after certain point in the human history when if one picked one side then the other picked the opposite side (and the reasoning is: just because)
Otherwise stated, we are not doing this way because ISO has done it or ISO has it that way, even technically is controverisal way to do things.
How many times, did you hear in the committee meetings when an argument is shut down just because ISO has done it?
They are not seeing each other's perspective and are really trying to recreate "the other world" in their own image.
Isn't it the same thing happening in the world in the last 30 years or so?

 

[3DDave]

Can't make a career over agreement, yet the toilet plunger made it across the border.

The greater the gap the more money to be made straddling it.