When all three datums are center planes and are perpendicular to each other 2

[rollingcloud]

This is a spherical part, with two holes that are perpendicular to each other. First of all, I know you cannot legally label datums on centerlines, so this drawing is incorrect. (And I would disagree with setting the mid planes as the datums. I would probably set the flat surface as the main datum and use the hole to establish the secondary datum axis.)

https://imgur.com/a/B6KufhV

But let's say it had properly established these center planes as the datums, I made an attempt shown in the relines. I am confused on whether not datum C and B create a datum axis at the intersection for the true position of the fastener holes. My guess is yes? Can someone please confirm?

 

[Wuzhee]

Datum plane A does not pass through the sphere center. It is offset by how much is the "flattened" part.
Datum plane C is correct.

What makes sense to me is the center hole as Datum B, then position the 4X hole pattern to A|B|C.

 

[Burunduk]

Please explain datum feature B.

 

[jassco]

Your datum features make no sense. These two views don't appear to show the same object. What is datum feature B?

Have a nice weekend!

Alex

 

[rollingcloud]

Wuzhee - Are you referring to the original datum A or the redline datum A?

 

[rollingcloud]

Datum B is supposed to be the center plane perpendicular to the other two datums planes. The redline datum B is also incorrect, as it still attempting to create the datum off a centerline. I am not sure how to legally callout that datum B. For the purpose of my original question, assume that the blue line is flat surface, and datum B is now legal as shown below:

https://imgur.com/a/5DBWUTb

And assume datum A pass through the center.
On the true position call out, does datum B and C create a datum axis through the center of the hole? I ask this because that basic dim 1.900 needs to be from the axis of the hole or a datum axis through the center of the hole. So, if datum B and C does not create the datum axis, the true position callout seems to be invalid due to the basic dim being invalid.

 

[Burunduk]

There will be no direct relationship to the hole axis because the center plane datums are derived from the flats, not the hole. As a result, the origin of measurements will be misaligned with the hole axis by a certain amount.

 

[jassco]

Hi, rollingcloud:

Datum features have sequences. According to your logic, datum feature B is related to datum feature C. Therefore, datum feature B should not precede datum feature C in your feature control frame for the hole (dia. 1.550/1.540).

Best regards,
Alex

 

[rollingcloud]

Thank you Alex. Good catch!

 

[rollingcloud]

Burunduk,
Thanks! That answered my main question! I wonder where I got the idea from, must have been confused with something close to it

 

[Brian Malone]

Rollingcloud,
this is an inquiry, not a dig: Is there a reason you do not use the Insert Image function (camera icon)?

The Imgur website is a sea of ads and clips that have nothing to do with what you are trying to present for review. Your original post had two images, and the latest has one, yet that has to be figured out by scrolling to ensure pertinent views are not missed in the sea of Imgur randomness . . .

 

[rollingcloud]

Brain - When I click on the link, it only shows my images, I am not seeing other ads. However, if Imgur is inconvenient, I will try to use the insert function as much as possible or maybe use Dropbox/Google services. This forum takes away the option to edit posts after certain amount of time I think. Just in case I make a bad mistake.

 

[Brian Malone]

I think the Eng-Tips Insert Image function works fairly well. Click on the Camera icon

and select the image file, click Done.

Your image is inserted directly into your text. Everyone will see exactly what you are trying to discuss without all the static of Imgur links.

Test image:

Some of the long-timers here can explain details on how they size images, etc.