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Medium planes of angle dimension as datum feature

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jassco

Mechanical
Feb 22, 2011
537
Hi, Folks:

Please take a look at image attached. I have 3 questions. I have been thinking about this for a while. I want to see if you have any suggestions.

Item #1: Is datum feature A valid (see top right)? Can I consider these two partial cone surfaces as a "Complex" datum feature?

Item #2: Is it OK to use "D - E" as a multiple datum feature (see bottom right)?

Item #3 and 4: Datum symbol B and F are obviously invalid (see left side). How do I use center plane of an angle as a datum feature?

This is a dummy drawing. I have a few features that need to be located in reference to datum feature A, B, and C.

Have a nice weekend!

Alex
 
 https://files.engineering.com/getfile.aspx?folder=0408c780-d8ad-444d-96f6-071f432b8ad9&file=Capture.JPG
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In your item #1 (section A-A) A is a valid datum feature, under the condition the angle between the two partial cones is basic and either is added to the drawing or the drawing indicates that basic dimensions are queried from the model.

The same is true for: multiple datum feature D-E at item #2 (section B-B) where a profile tolerance is needed to control the angle, and datum features B and F, for which the 112° needs to be basic and also controlled by profile.

Also note that:
In the feature control frame that references |A|B|C| C is redundant as A primary and B secondary establish a 6 DOF constraining DRF.
In the feature control frame that references |D-E|G|F| G as secondary is redundant as it is unable to constrain any DOF that were not already constrained by D-E.
 
Hi, Burunduk:

Thanks a lot for your quick response! Yes, you are correct that the 3rd datum are redundant datum feature, and should be removed.

Now, I do have another question. Please take a look at this image attached.

Item #3 and #4: I use Solidworks 2020. It does not allow me to attach datum symbol B and F to the BASIC angle dimension (120 degrees). Is it Ok to attach datum symbol B and F to align with dimension lines as shown with items #5 and #6? I want to interpret them as derived medium planes of angles. Or, is there such a thing? Generally, derived medium planes are meant for features of size, like a tab or a slot. Are placements of these two datum symbols (B and F) allowed by ASME Y14.5-2009, or 2018 standards?

Best regards,

Alex
 
 https://files.engineering.com/getfile.aspx?folder=055dd255-7288-48f4-8b71-651dfdd416f6&file=Capture.JPG
Jassco, there is nothing in ASME Y14.5 (any edition) that defines the meaning of a datum feature symbol aligned with the dimension line of an angle dimension.

I would suggest one of the following:

1. Specify the two faces which are at 112° to each other as a Complex datum feature similarly to datum feature A.

2. Specify the two faces as a Multiple Datum Feature similarly to D-E.

3. To define datum feature B (or F) designate one of the faces as datum target area B1 (or F1) and the face at the other side of the angle as datum target area B2 (or F2). Show a direct view of each of these faces with hatching of the complete surface and attach a datum target symbol with a leader that ends with a filled dot on the surface.

The third option may be considered a bit unusual as datum targets are usually used to designate limited areas or elements of a surface but not full surfaces, but I think that this method is nevertheless perfectly interpretable per the Y14.5 standard.
 
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