Doubt on datum

[Vimalmechs]

Hi all,

PFA. this is a single part. After wire cutting done from a disc. There will be 3 pieces from one disc.
here my doubt is how this GD&T frame applies during production of this part(before wire cutting into 3 pieces).I wanto drill the holes before wire cutting.but c datum surface wont be there before wire cutting operation.
"C datum" is imaginary during production of the disc.

hope to hear back.

 

[pmarc]

Please remove "&" symbol from file name. We are not able to see it.

 

[CheckerHater]

how this GD&T frame applies during production of this part(before wire cutting into 3 pieces).

GD&T frame has nothing to do with the production of the part. You do no use GD&T "before" something happens.
Your drawing should always represent FINAL state of the part AFTER the manufacturing is finished.
With some exceptions, you should never place a reference to non-existing geometry on your drawing.
If you have no other choice, as an exception, you can use “NON-MANDATORY” note.
If you re-post your picture without using symbol “&” in the file name, we will be able to provide you with further advice.

 

[CheckerHater]

Another important thing to consider:

After your part is cut into 3 pieces, are they used independently from each other, or are they bound to work together as a set?
(As you can see, once we actually know how your part looks like, we can have lot of fun with it.)

P.S. Forgot the most important question of them all: ASME or ISO?

 

[Vimalmechs]

Hi CH,

Parts are functioning independently. As well its ASME.

 

[CheckerHater]

Thank you for the input.
You shouldn’t worry about datum C not existing before the final cut, because like I mentioned, we describe the final state. Let say you use datum C for measuring the part. Do you care where the rest of the circle is?
Using radius as a datum was discussed many times, opinions differ, but generally it’s considered possible.
What I don’t see on your drawing are basic dimensions connecting datums to holes (not all of them).
Unfortunately I have to leave now, but I will try to get back ASAP

 

[pmarc]

I agree with CH that you should not worry about datum feature C not existing before the final cut.

I got however more questions:
1. Is datum feature C selected based on how the part functions (that is, how it is oriented and located in an assembly) or does it just serve as "clocking" datum feature in order to control angular relationship between two holes and sides of the plate?
2. How are both arcs (inner and outer) dimensioned and toleranced?

 

[Vimalmechs]

Hi,

PFA.

I have received this drawing as per the fig 1. The three parts works independently (maintaining 120 degrees in one plane). The hole pattern can rotate as per fig 1. To arrest the rotation, i have suggested to define datum C as "clocking" datum.

Fig 2. represents the modified drawing.

 

[Vimalmechs]

Submitting with Attachment