Tolerance relative to datum lines

[edgeofmagic]

If I specify X and Y datum lines, and override the default tolerance on certain features with comments to machinist, is it safe for me to assume that those tolerances will be considered as positional tolerances relative to the datum origin (unless otherwise stated in the comments)?

[Tech2]

Please post an example.

[edgeofmagic]

I've attached an example, as requested. In the attachment, the datum lines are in top view, comments to machinist in top and back views. My intent with the top view comment was that the surface defined by the upper edge of the of the tr@pezoidal* shape (indicated by the arrow) should be within +/- 0.002" tolerance, relative to the datum origin. Similarly, on the back view, my intent was that the surface defined by the rightmost vertical side of the rectangle (indicated by the arrow) should be within +/- 0.002" tolerance with respect to the datum origin specified in the top view.

It may help to clarify if I explain the need for the constraint. The two surfaces indicated for tighter tolerances contact another part in an assembly. That part slides along the Z axis of the part in the attached file. The other part contains a circular feature whose axis must align with the datum origin on this part, particularly with the hole in the bottom view. I've tried (not being a mechanical engineer) to calculate the tolerance stack across both parts to keep the necessary alignment within +/- 0.01".

Thanks very much for your help. I hope this description was sufficiently clear.

*I had to misspell tr@pezoidal intentionally, because the forum posting filter interpreted it as "r@pe" and wouldn't let me post. Sorry for the awkward orthography.

[Tech2]

You should label the datums (e.g. A,B) and should specify that your tolerance applies to Position.
Also you should clarify in the Back view that you are controlling only the one side of the feature by showing an explicit dimension between that side and the datum in addition to the tolerance designation.

[edgeofmagic]

Thank you very much. When specifying that tolerance applies to position (as per your message), should I indicate this in text, or attempt to reproduce the GD&T symbols?

By the way, when I log into the forum, I'm told that I have a new private message (I also received a notification email). When I click on the link to get the message, I'm told "Private messaging has been disabled on this board." Is there something I can do to read this message?

[Tech2]

It is preferred to use the symbols. I don't know why you might have received a message and am not aware of any way to get msgs.