Flatness and Target Datums

[TigerShark]

Hello Frineds,

There is a question here : when we have 3 target area for datum-A, ( 3 circles)on drawing and there is a flatness call for datum-A as well ( all points are in same level, actually datum-A is flat plane). target datums for A are just small areas of plane. I have used those 3 zones for alignment ONLY but to measure Flatness I have taken more points outside of Datum Zones. otherwise the part functioin will be absolutely affetced ( if you leave the Plane and only conside 3 zone for target A). Some body say, NO, we have to only measure flatness by using the Target Area points only. I do not belive so, what you think?

Thank you

[bw_bob]

In my opinion the 3 datum targets are datum -A-. They were put on the print to create datum -A-. I would measure 3 targets & report flatness.

I would also report the total flatness for reference only.

[Farmer]

What bob said.

You are fully covered then.

[Matthew D. Hoedeman]

Well, take more than 3 hits. Take several in each of the target zones. A 3-hit plane will ALWAYS be perfectly flat.

If the print calls out the 3 zones as DATUM A, and has a callout FOR Datum-A for the flatness, then ONLY those 3 zones are for the callout.

[TigerShark]

What bob said.

You are fully covered then.

I will be covered for datuming only But the problem is, part is Abviously Bended on some areas ( not in target zones), and by this way I report that it is OK ( if I measure only Target Area to measure flatness).

[bw_bob]

I will be covered for datuming only But the problem is, part is Abviously Bended on some areas ( not in target zones), and by this way I report that it is OK ( if I measure only Target Area to measure flatness).

But the target zones represent datum -A- they may be the only area that actually touches. It really does'nt matter because thats how it is defined on the print....and like Matt said take numerous points for each area & create datum -A-

[VONDY]

I disagree, if you have a surface called datum -A- and it has 3 target points for it. You can't use only those 3 points as then it would always be perfectly flat, you would need to check the whole surface. Flatness for this type of call out to me should not be used, either straightness or cylindricity should maybe have been used. This is my opine and without actually seeing the print I can't be certain that I am on the same page as you.

Tigershark and the rest of the forum - Sorry for the bad reply - I had a flash back to when one of our Engineers came down with a tube that had 3 target circles in it - I lost it then and this time I didn't completely read your whole question - I should have had the drugs - and probably a little, um' a lot of beer. Not sure about the lady though

I do agree that a print would be nice. Normally target points are for a fixture to sit on a certain sized locator's, then the flatness usually covers the rest of the surface. Then again, looking at the print might change my mind.

[Farmer]

I disagree, if you have a surface called datum -A- and it has 3 target points for it. You can't use only those 3 points as then it would always be perfectly flat, you would need to check the whole surface. Flatness for this type of call out to me should not be used, either straighness or cylindricity should maybe have been used. This is my opion and without actually seeing the print I can't be certain that I am on the same page as you.

There are 3 target circles, not points (If I'm reading it right). So as long as he takes more points than the mathematical minimum he will be able to measure the form.

[bw_bob]

Datum-A- is defined by 3 target zones. That is datum-A-.....but i worship shrubs ????

[craiger_ny]

Datum-A- is defined by 3 target zones. That is datum-A-.....but i worship shrubs ????

I agree, and I do drugs.

[Matthew D. Hoedeman]

I agree, and I do drugs.

AND, old tattoo'd ladies with multiple body piercings.

[craiger_ny]

AND, old tattoo'd ladies with multiple body piercings.

Yes but not before doing the drugs though.

[cmmguy]

Without the drawing it is impossible to say what the real answer is.

I would agree, the targets represent datum A, BUT does the flatness actually apply to datum A or the surface that contains datum A?

[craiger_ny]

Also worth noting is that flatness as a callout can be attached in more than one way. How it is attached denotes the effect of flatness in regards to the size of the feature. Perhaps a drawing or sketch would help.

[Jan d.]

What Craiger said. Please attach the exact call.

Jan.