How would you create Datum B from these 4 holes

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How would you create Datum B from the 4 holes shown below?

2020-05-08 09_54_23-Window.jpg

[Mikeg]

My opinion would say this an error, but as we know all prints are different and even when it goes against all rules they still dimension however they want to and its up to us to translate what they mean. Is it possible to show pictures of the other datums so we can understand and hopefully help.

[[email protected]]

Datum A is the bottom of the part. There are no other Datums.

[A-machine-insp]

The two options I see are 1: Run the circles using 1 or 3 sample hits to set the actual height, construct points for each circle, then construct a plane. If that was their intent though, I would have called the place the datum. Or 2: Do the above but create a center point from the 4 points constructed at each circle.

What is being dimensioned to Datum B? If it is a true position I would lean towards option 2. They may be wanting to hold another set of circles to the Datum B circles.

I agree though, it is a bad callout.

[DAN_M]

Terrible callout. I would get clarification from the customer before you invest time in measuring something the wrong way.

[Schlag]

Am I missing something ? Don't you guys see hole patterns called as DATUMS on a regular basis ? What the print doesnt show would have to be a locator for B. Im guessing the Ends of the part would be a profile back to B ? I can only assume ? It's a different way of thinking. Rather than 2 edges being your 0.0. the Pattern is 0.0. THink of it this way. What if the part was bolted down and the entire outside edge of part was just clearance and served no function ? Why dimension the holes to an edge of the part ? Dimension the edge of the part to the holes. And thats what we cant see on this drawing. The callout we do see is for the pattern and the perp to A.

[Mikeg]

Then Datum B is useless anyways. you can report the 4 hole pattern using the dimensions you have or contact the customer and ask for clarification.

[Schlag]

How is the DATUM useless based on the portion of the print you are seeing ?

[Mikeg]

Its not useless if any other features relate back to it, I took it as nothing else did by comments. Hope I made your day better

[RandomJerk]

If the leader were attached to the FCF, it would be acceptable per the 2009 standard, para. 3.4.6, fig. 3-27. Patterns are acceptable datum features, in this case it would appear that, based on "usual" precedence, you would level to A then 2D best fit the pattern, rotation and translation, and that will become your rotational constraint. Only do that if the holes are programmed to the correct nominals, however.

[Schlag]

I think the leaders are attached but the print has been extremely sanitized with all the " white boxes " over portions of the print ?

[RandomJerk]

Schlag - possibly, but we both what happens if you assume something around here thought I'd just go with what was presented.

[SteveatNordson]

Settings editor ...DatumLevelToCircle...set the parameter to 1. I believe this will create points at the surface where the circle pierces the top plane. It also sounds like it was designed for exactly what you need to do.

[AndersI]

If you're using XactMeasure just create a group of the four holes, dimension the group, and call the group Datum B.

[vpt.se]

Like Matt said, just throw them into a feature set and define the set as datum B.

[dwade]

Best fit rotation and origin for the hole pattern. Should work in any version of the DEMON

[BIGWIG7]

^THIS. Best fit that B all day.

[balaji]

Hi
I got a part with 8 holes located on a eleptical form which is called datum B.DatA is a irregular profile .its a sheet metal part if 1.9mm thickness. Datum A is a form not a flat plane.Any suggestions for aligning the part will be much appreciated.

[Schlag]

start a new post. no one will help help out on a " post in a post "

[ogcharliebrown]

What I see is 4 .128 holes with one hole as datum B.

[jtrofatter]

Agree! true it could be a super **** print, but typically the datum symbol would be connected to the FCF, as RandomJerk mentioned above

[UKCMM]

The drawing as posted is ambiguous it would be normal practice to attach the Datum leader to the FCF if the pattern was to be used as the Datum, I would contact the customer for clarification.

[Schlag]

It says 4x right behind it. Use the pattern as B. We all know all 4 holes are 99.9% machined in same op so deep down it probably doesnt matter....

[Robert Hulman]

I would do feature set