Question Regarding Multiple Datum Planes with Flatness Callout

[Kevin G]

Hi Everyone,

I have a question regarding how flatness should be check on multiple datum planes.


Side Section View

Top View

Would I check flatness of these areas locally excluding each other datum?

Or are they checked together. For example would I put the part on the checking fixture unclamped and slide a feeler under each Datum net pad area?

Or are the areas in between and around each datum considered in the flatness call out?

Thank you,

 

[drawoh]

Kevin G,

Your drawings are scaled rather small, which makes them hard to read. On your top view, I believe I see datum targets defining datum[ ]A. Since the datum is defined by three points, there is no concept of flatness.

The side section view shows another datum[ ]A feature. This is wrong. Datum[ ]A either is defined by datum targets, or it is defined by (I assume) those two surfaces. You can test those two surfaces for co-planarity and flatness. This is sheet metal, so the designer should have allowed for sloppy tolerances. The second datum[ ]A face requires a profile tolerance of around 0.8mm with respect to the other datum[ ]A face.

The drawing sucks.

You should call your customer/drafter and ask them what they really want.

--
JHG

 

[Belanger]

That flatness callout has nothing to do with datum A. The flatness is to be checked on the surface that is being pointed to.

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

 

[drawoh]

Belanger,

I am interpreting datum[ ]A on the left view, as two surfaces that must be maintained flat somehow. I could be wrong. It looks like a construction line is connecting the two surfaces, which also has a datum box attached to it. It is not a very good drawing.

If I apply flatness to two connected faces, they must be co-planar, right?

--
JHG

 

[Belanger]

drawoh... The answer to your last question is no. Flatness could be applied to multiples surfaces that are intended to be coplanar, but flatness is powerless to control coplanarity (unless they add CF). That would be a job for profile of a surface.

But I'm simply looking at the feature control frame for flatness. It's attached to an extension line that goes to that one flat surface. As soon as that surface stops (at the trough), then the flatness control stops.
Maybe the idea was to have the flatness apply across multiple surfaces (beyond the trough), but there is no note to that effect. And even if there were a 2X or 2 SURFACES note, it wouldn't control coplanarity.

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

 

[Burunduk]

It is allowed to use both a datum feature symbol and datum targets with the same letter on the same feature or group of features. Although in this particular case, it was executed in a very confusing way for many reasons, some of them were mentioned in the previous replies.

The main thing I'm concerned about is that the two views don't seem to belong to the same part. Either that or the "top view" is missing many lines. Where in the top view is the interruption between the two coplanar surfaces shown at the right side of the side view? And where is the transition between heights that should be at about one-third of the part length from the right?

 

[CheckerHater]

Looks like the "side" view is the view from the left, rotated:

Not like it helps a lot

"For every expert there is an equal and opposite expert"
Arthur C. Clarke Profiles of the future

 

[Kevin G]

Thanks everyone for your help.