Gage Design on DRF through two holes

[SeasonLee]

Attached is a snap shot from page 66~68 of ASME Y14.43-2003 Dimensioning and Tolerancing Principles for Gages and Fixtrues, few questions arose while I studied the gage design on this part, anyone who can give me your comments and interpretation on the following questions. There is no doubt on the 1st gage, my question is on the 2nd gage on page 3.

1. The diamond pin on datum E is moveable sliding design, does datum E always designed in movable sliding base? The other book mentioned the datum pins are fixed on the base plate if the datum modified with MMC, the book also said the datum pin is movable if the datum is RFS, it seems there is a conflict on this gage design.

2. If the two holes (datum D and E) changed as a datum feature D, the four holes Ø5.1~5.2 position callout will be: |Position|Ø1MMC|A|D circle M|.
How about the datum pin gage design now? Are there any differences on the gage design?

Thanks for all inputs

SeasonLee

 

[Belanger]

It's late at night, so my thinking might not be terribly solid, but my first inclination was that this has something to do with the idea of "translation." Of course, the Y14.43 standard was around before Y14.5 came up with the translation modifier. But this still might play into that very idea.

However, the translation modifier seems of use mainly for when the datums are RMB. And that is the idea that your "other book" is mentioning, even if it was before the datum translation modifier came around: RFS/RMB would require the datum simulator to center itself on the tertiary datum feature, even if it's off center. So I think that you are on to something: if these datum references D and E are modified with "M," then the pins simulating those datums should probably be fixed in location, since their location error will already be factored into the size of the pins simulating them (virtual condition).

If the holes currently labeled as D and E were the same size, and also paired up as a single datum callout, then I agree their location would also be fixed.

John-Paul Belanger
Certified Sr. GD&T Professional
Geometric Learning Systems

 

[CheckerHater]

Didn't have enough sleep last night, so I can relate to John Paul .

I see it as discrepancy between "theoretically perfect" fixture design and "good enough for real life".

If your part has features intended for precise location, say, to be engaged with dowels; they will be accurate enough to fit over fixed diamond pin. The diamond pin being "relieved" in two directions should be good enough to clock the part, so it's either sliding round pin, or fixed diamond.

The drawing actually sais that sliding pin could be cylindrical. But wait, there is more! (tm) Look at diamond pin top view. There is diameter symbol in FCF! how could sliding pin have cylindrical tolerance zone?

I guess at some point "sliding round or fixed diamond" was considered, but last minute changes were made when preparing standard for release, leaving loophole allowing for multiple interpretations.
After all, nobody is perfect.

Just my 2 cents. Like I said, cannot think clearly just yet.

 

[pmarc]

SeasonLee,
Datum feature E simulator is not fixed in location wrt datum feature simulator D, because on part's drawing the lower FCF for two 6.5-6.6 holes does not control position but perpendicularity. Per nature such callout does not fix the distance between simulators D & E.

CheckerHater,
The diameter symbol for position of diamond pin is there because the requirement is that the pin cannot violate cylindrical virtual condition boundary. It is in fact not important whether the tips of the diamond pin are oriented horizontally or vertically to higher precedence datums. Everything will be fine as long as they do not violate dia. 6.5 boundary.

 

[pmarc]

Of course there should 6.51 in the last sentence of my previous post. Appologies for mistake.

 

[Belanger]

That makes sense regarding datum E -- I knew that Daylight Savings change affected my brain somehow. Only if E itself were positioned back to D would the distance between them need to be fixed when gaging the 1 mm FCFs.



John-Paul Belanger
Certified Sr. GD&T Professional
Geometric Learning Systems

 

[CheckerHater]

pmarc, would you please clarify: are you saying orientation of diamond pin tips is irrelevant?

 

[PaulJackson]

Diameter [E] has to be perpendicular to [A] within 0(M) in all rotational directions the same as [D]... therefore since the dowel spread's translational freedom has been provided in the slide... I believe it would be proper to use the round pin rather than the diamond pin on the second gage.

Paul

 

[pmarc]

CheckerHater,
I am saying that immaginary line connecting quadrants of both diamond pin round tips does not have to be parallel to datum plane C of the part like it is shown in Figure B10(c). In reality the pin can be mounted in a gage in a way that this virtual line is at any angle to C. The only thing important is that those tips cannot extend the virtual condition boundary.

 

[SeasonLee]

Thanks for all inputs.

Are there any changes on the gage design if DRF change to hole pattern as datum feature :
| Pos | Ø1 M | A | D circle M |

SeasonLee

 

[pmarc]

Yep, two cylindrical pins simulating datum feature D would have to be fixed in size and location with relation to each other (basic 70). The size of those pins and their positional tolerance value would depend on chosen gaging policy.

 

[SeasonLee]

Thanks for your prompt input, pmarc. Further questions :

If the four holes Ø5.1~5.2 FCF change to RFS : |pos|Ø1|A|D|, any changes on the gage design as compared with |pos|Ø1 M|A|D circle M| ?

SeasonLee

 

[pmarc]

Yes, changes would be needed.
The gage pins would still be fixed in location relative to each other (basic 70) but their size would have to be adjustable to assure maximum possible contact between simulator pins and datum feature holes.