Drafting: Datum on a curved surface

[DLH81]

I am wondering if there is a way to hang a datum off of a curved surface. See attached picture which shows what I want to do. I was able to accomplish the view in the picture by going into active sketch view, zooming in on the tangent point of the curve and putting in a tiny line that I could then hook the datum to. I'd prefer to be able to put it on the part itself so that it is associative if this is possible?

NX 8.0/TC8

 

[Xwheelguy]

So no dimensions on this surface, just a datum?

Tim Flater
NX Designer
NX 8.0.3.4
Win7 Pro x64 SP1
Intel Xeon 2.53 GHz 6GB RAM
NVIDIA Quadro 4000 2GB

 

[DLH81]

There are dimensions also. I didn't show them just for clarity. The dimensions are easy to tag to the tangent point of the arc.

Are you getting at hanging the datum off the extension line of the dimension? That kind of works, but I am unable to slide the datum down below the arrows of the dimension. I can slide it up along the extension line, but it needs to be down below all the dimensions.

NX 8.0/TC8

 

[Xwheelguy]

Firstly, while I will not debate what must and cannot be done on your drawing, I think it's important to note that if something with a datum callout cannot be done, then you are more than likely not violating any standard, as Siemens (and all of the previous NX "owners") are pretty diligent about abiding by existing standards. If you can fit the datum on one of the extension lines, then I'd do it. It's not "wrong", and you'd probably have a tough time convincing the powers that be that it needs to be added, since a dimension's extension line is "standard".

How about a leader with no text (or a [space]) with the datum coming off the stub, like a Radius dimension would have the datum on the stub?

If the suface is a true arc, you should be able to attach the datum flag to the arc. If not, then ignore this suggestion.

You can set the Type to Flag in the Datum Feature and pull that off of an extension line, but that's not what you're showing in your image.

In a manner of speaking, your initial method (as a sketch in drafting) should be associative, if you've geometrically constrained the line to the arc/surface properly. If the arc/surface moves, then so should the line, unless you completely delete the surface/face.

Tim Flater
NX Designer
NX 8.0.3.4
Win7 Pro x64 SP1
Intel Xeon 2.53 GHz 6GB RAM
NVIDIA Quadro 4000 2GB

 

[jerry1423]

Is what i attached a good, and legal, way to do it ?

 

[jerry1423]

I really don't think it is legal to have a curved surface as datum A.

 

[SvenBom]

OK, if you managed to place Datum Feature Symbol ('C') on a curved surface. But what kind of Feature control Frame or GD&T are you tring to place according to this Datum? Can you upload the image of the whole view?

 

[jerry1423]

Let's not get into that SvenBOM.

 

[DLH81]

Thanks XWheelGuy for the suggestions (and for not trying to debate what can and cannot be done!). You are correct, if the sketch line is properly constrained, it is associative.


I attached another example that has the same issue, but perhaps is a bit more of a common scenerio and I don't think anyone can debate the legality of it! It is just a simple extruded circle and I am calling one of the flat surfaces datum A. Since it is a circle, and in the right side view the edge is actually an arc, I cannot grab it to drag my datum down as shown. If it were an extruded rectangle, I would be able to grab that edge. The way I was able to create the datum A shown in this case was to put in a dimension across the width of the part, turn off all the arrows, the text and the left extnesion line, then hook the datum A to the right extension line. This just seems like a painful process to go through to get the desired result so I'm wondering if there is an easier way other than this?

Also, before anyone tries to tell me I can just hook the datum onto the face of the part, I'm aware that is a legal way to represent the datum, but as I'm sure many of you can relate to, there are many people at my work that have seen it done the way shown in the picture for 30+ years and refuse to change their ways.

NX 8.0/TC8

 

[jerry1423]

In the sitution you shown in this last image; I agree there should be a better way to attach the datum to this surface (when the curved surface is viewed as straight) but for now there isn't a way.
What I do is attach the datum to a dimension extention line.

 

[SvenBom]

Maybe it would be easier to draw a line and place Datum on this line:
1. right click on the view and select Activate Sketch View
2. draw a line from the appropriate end point (selection scope must not be set to Within Active Sketch Only)
3. finish the sketch
4. place the Datum on this line
With this method, it is much easier then placing the dimension first and then hiding all the geometry, that must not be shown.
Hope this helps in reducing the steps for placing the Datum.

 

[jerry1423]

I said nothing about hiding any geometry.
Just place the dimension and attach the datum to the extention line from that dimension.

 

[jerry1423]

and I hope you are using view dependent editing when working with "hiding" curves in a view instead of Hide.
You will run into trouble if you are not

 

[Xwheelguy]

Jerry,

I believe the OP was stating that the method he used in the second attachment involved hiding the dims - just as a way of letting us know the route he took for that datum feature appearance. Sven was just pointing out that adding a sketch or view dependent curve was probably eaier than going through the OP's hiding method.

I agree with you in that Datum Feature extension lines need to be addressed for a few things, especially the side view of a cylinder or curved shape like the OP has.

Tim Flater
NX Designer
NX 8.0.3.4
Win7 Pro x64 SP1
Intel Xeon 2.53 GHz 6GB RAM
NVIDIA Quadro 4000 2GB