Reporting true position of a hole pattern

[aliptpatel]

Hello everyone,

I have always seen a debate at least at the places I have worked about reporting true position of hole patterns. There have been many times that our customer asking to report the individual true position of 16X (a random number) holes instead of one single true position of the pattern. I also have tried to read ASME 14.5Y 2009 but can't find any introduction to that so I thought that this concept was introduced many years ago. Also we get our tools and molds made from outside vendors and they also report true positions of hole individually even though the callout is shown in the image below. So I wan to know how everyone else report the true position? I use TEXT ONLY for my measurement output. Also I CHECK-MARK ON Text mode dimension reporting and UNCHECKED Text mode dimension reporting. I have attached example of both of them.

[JacobCheverie]

You have MMB on datum -B-. This will allow for datum shift. Simultaneous requirement states the holes in the pattern must be measured simultaneously. There is an option in PC-DMIS for simultaneous evaluation, that is what you need.

[aliptpatel]

Thanks Jacob. I forgot to mention that I am using 6- axis Romer Absolute arm and Manual measurement. Also use Xactmeasure for GD&T. The MMB on datum B is incorrect as the feature that creates datum B has a reference diameter.

[Schlag]

I would dimension each hole individually. Yes, its simultaneous but it doesn't mean its a pattern. I mean it could be 7 x 2 hole patterns. Hypothetically, what if every hole is perfect except 1 ? It shows the pattern bad, now would adjust that ? You cant with a simple offset change. You need to know where ALL the holes are. The feature that creates B has a ref Ø ? If its ref it has to be a print mistake. You're not confusing REF with BASIC are you ? It happens.

[aliptpatel]

I have the similar concern that what if only one hole is way out of tolerance? Thats why I usually report the values in the format that shows all the values of true position individually( 2nd image in the attachment) but still report it as a hole pattern in Xactmeasure. But still don't know what does that callout actually mean in the standards? Does ASME 14.5Y says to report simultaneously? If yes then can someone show me the link or tell me article and page number of the version it says that?

[Schlag]

Anything controlled by the same DATUM STRUCTURE is auotmaticially simultaneous. Yes, the standard call this a pattern but I think that's kinda vague. Like I said, It could be 7 2 hole patterns as well. The design intent decides this and that is not always clear from a print. I wouldn't report it that way as that information is "usually" useless to manufacturing. If its truly a pattern it should be a composite but that is asking too much from most engineers / drafters. We could only wish GD&T was correct at least 51% of the time.

PAGE 76 Y14.5-2009 SECTION 4.19

[KIRBSTER269]

imagine putting a wheel on a car one hole at a time. actually that would be a pattern, but you get the jist of it

[Schlag]

Yeah. I have my certification on Y14.5 thru ASME. I get the gist of it.

[Schrocknroll]

When filling out a report when there is only one characteristic(balloon) number I will put the worst deviation. For the CMM report I always have all the holes reported individually, but simultaneously as has been mentioned by others.

[vpt.se]

It is the position of the 16 holes evaluated together that is interesting, which means the XactMeasure report. Think of how a gage would look - you'd have 16 pins for each hole and a pin for the datum - not one pin for the hole that you rotate to each hole 16 times. The text mode report is only reporting the centroid for the group which I doubt is interesting...

[MikeD6]

Controlling a pattern compared to individual holes allows you to control the pattern tighter to itself than to the datum structure. The hole pattern can drift around the part somewhat, but the pattern must be controlled tightly. I think of a sand casted flange with a secondary machining step to machine one side flat and drill a hole pattern. It may not matter if the hole pattern isn't perfectly centered on the flange, but the distances between the holes is important. So, you are still reporting out the position of the individual holes, not the centroid of the pattern. And Schlag is right, it should be an composite FCF.

[AndersI]

*IF* the datums lock all six DOF, *AND* there's no MMB, the result will be the same when dimensioning individually or as a group. In all other cases it's an error to dimension individually if they are marked as a group. Do note that (at least) in ISO-land, holes placed around a common center point/axis have always been an implicit group, and any MMB, or unlocked degree of freedom (as in the example picture in the OP) will cause individual dimensioning to be wrong, as there may be a separate datum fit for every hole.

The above goes for FCF (XactMeasure) - when you're doing legacy, you're always locking all six DOF with your alignment (and probably ignoring MMB), so the question is moot there.

[KIRBSTER269]

All You have to do is ask the engineer "Are these 14 holes for 14 individual mating parts, or are they for one mating part?"