Datum interpretation 4

[SeasonLee]

Attached print is a fiber glass reinforced resin molded part, my question is:

1.The pivot hole is datum B, section B-B defined the datum, but I can’t image how to set up the datum, it’s a datum point, datum line or datum area?

2.There is a position callout on the pivot hole, can we use the pinot hole itself as a 2nd reference datum in the DRF?

Thanks in advance for the replies.

SaesonLee

 

[SeasonLee]

Don, thanks for your interpretation.

If the second plane passes through the two datum points (not the axis of the pivot hole), then I am imaging where is the datum point 0,0,0.

Thanks

SeasonLee

 

[GDTcoach]

The 0,0,0 is where the 3 datum planes of the datum reference frame intersect.
Is datum axis A the "axis derived from the datum feature simulator" as John-Paul said or is that the simulated datum axis? Some of these arguments, to the layman, are a distinction without a difference. In the 1966 Standard we showed datum planes as existing in a milling machine and a lathe. The standard talked about using datum features to immobilize the part and align it to the datum reference frame found in this processing equipment. The figures were removed because they were too practical. I think they are great figures to explain what we are trying to do with datum features. Getting hung up on some of the theoretical terminology doesn't help folks understand the important concepts, in my opinion. Of course, if you want to get certified, you better know them.

 

[SeasonLee]

Sorry for late to get the mating part print, please take a look on the Cover print, it will help us to have a better understanding on its function and the designer intent, my questions:

1. As we discussed earlier the Case pivot hole position callout is
|POS|Ø.020|A|B| where datum B is the pivot hole itself (and assigned as secondary datum feature).
The Cover pivot hole position callout is
|POS|Ø.024|A|C| where datum C is the width between holes (and assigned as tertiary datum feature)
My first question is why not to use the pivot hole (datum B) itself on the position FCF?

2. The secondary datum feature is defined by|POS|Ø.024|A|C|, can we use tertiary datum C to define the secondary datum feature B? I think we can’t, but I want to be sure.

3. Datum point B1 is located on a counterbore, B2 is on the through hole, so they are on a different feature, can we use these two datum points to establish second plane as we discussed on the Case earlier, I think we can’t. I will think B1 / B2 should be datum target lines (a circular line) here.

4. For the Case, I will image the datum point o,o,o at the center point of the pivot hole as shown on the attached print, from the design viewpoint, the datum point for the Cover should be at the corresponding point, is it correct?

5. Again, still need to ask: can we simply plug a best fit gage pin to simulate the datum B?

Thanks again for the inputs

SeasonLee

 

[SeasonLee]

Owing to the upload file size, have to upload separately, here is the Case datum point 0,0,0 print.

Thanks

 

[powerhound]

This shows the zeroes in two axes; let's say X and Y. Exactly where are you saying the Z zero point is?

Powerhound, GDTP T-0419
Engineering Technician
Inventor 2010
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[SeasonLee]

You are right, Powerhound
Thanks

SeasonLee