Datums on Angular Dimensions

[Under_Score]

Hi,

I'm currently working on a drawing for a part that requires two round studs to be centered on the part relative to the outside edges of the part. The two studs (Ø.063) are currently controlled using datums A and B, but I want to add a third datum C to control the last DOF. My initial thought was to add datum C to the 15.0° angular dimension, but SolidWorks indicates that "Only 1982 style datums can be placed on angular dimensions." What is a correct way to place a datum in the center of this part using the surfaces currently controlled by the 15.0° dimension?

 

[drawoh]

Under_Score,

When I select a feature of size datum feature, I prefer something accurate. How are you doing to fixture to an inaccurate angle? I suggest using one of your studs as an FOS datum feature. Use a profile tolerance to control your outline.

--
JHG

 

[greenimi]

....... but I want to add a third datum C to control the last DOF

The question is why? Why the remaning degree of freedom should be arrested or stopped? What is the physical reality of this assembly?

Can the simultaneous requirement do the job ?

Profile all around for the outside feature (along with basic for radii and angles ex: .060, 35°, 615, 15°, 365, 190) and I think you are good to go.

 

[TheTick]

Make one of the holes a datum and control the outline relative to the hole position.

 

[powerhound]

Leave datum A, change datum feature B to the 2-stud pattern, change the position callout to just the lower frame of the feature control frame, then use profile of a surface to control the outside edges of the part to A|B|.

John Acosta, GDTP Senior Level
Manufacturing Engineering Tech

 

[CheckerHater]

You don't have to use angular surfaces for datum.
Your datum A constrains 3 degrees of freedom
Your datum B constrains 2 degrees of freedom
To constrain 1 remaining DOF make dimension .365 datum C
Your part is now fully constrained

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

 

[pylfrm]

What is a correct way to place a datum in the center of this part using the surfaces currently controlled by the 15.0° dimension?

[ol 1]
[li]Add basic dimensions to define the relationship between datum feature B and the two angled surfaces. One option would be to change the 15.0° dimension from toleranced to basic, and add a basic dimension from datum feature B to the theoretical intersection of the angled surfaces.[/li]
[li]Apply a profile of a surface tolerance to the two angled surfaces, referencing datum features A (primary) and B (secondary). Use a single feature control frame with two leaders.[/li]
[li]Identify the two angled surfaces as datum feature C by attaching a datum feature symbol to the profile of a surface feature control frame.[/li]
[li]Reference datum features A (primary), B (secondary), and C (tertiary) in the upper segment of the position tolerance.[/li]
[/ol]


I'm not saying this is a good idea, but you didn't ask that.

pylfrm

 

[Under_Score]

Everybody, thank you for the help. The first four responses suggested to control the outside profile relative to the stud pattern, and I've tried to do that:

Also, thank you CheckerHater and pylfrm for your responses. Thank you pylfrm for most directly answering my question. I will keep your suggested steps in mind for the future.

 

[Belanger]

You'll probably want to add an MMB modifier to the profile's datum B reference (near right edge of drawing), because the datum is created from a pattern of features. It depends on function, of course.

 

[Under_Score]

Good catch, Belanger. An MMB modifier does make sense for the function of this part. I'll add it. Thanks.