Establishing hole pattern datums

[Kyle2]

Hello all,
I have a hole pattern on a plate; the pattern's location on the plate has a loose tolerance, as does the form of the plate, but the relationship between the pattern's holes must be tightly controlled to allow the mating part to attach properly.
What is the correct way to tolerance this hole pattern?

A colleague suggested the following scheme:
Let's say I have a 4x .500 hole pattern arranged in a square. The position of one of the holes is given by basic dimensions from the edges of the plate (Datums A and B) and the positions of the other 3 holes are given by basic dimensions from the first hole. The first hole is assigned Datum C. The tolerance block points at the first hole (Datum C), has two frames and looks something like this:
4X .500 Thru All
[position][.030][A]
[position][.005][C]

This seems vague and/or wrong to me, but I can't find a good example on how to dimensions something like this in Y14.5-2009.
Any suggestions on how I might proceed?

ps. appologies for the description, I can't upload files on account of my employer's gateway.

 

[pmarc]

This sounds to be a typical application for composite positional tolerancing. See paragraph 7.5 and figure 7-38 for instance.

 

[Kyle2]

Aha! so it is, thanks!

 

[SeasonLee]

Prosody

Would you mind to post a sketch? For a composite position tolerance, the lower segment datum reference must be a subset of the upper segment, it means any datum references must be repeats and in the same order of the datums from upper segment, but the lower segment datum reference C is not a repeat on the OP, so I will think it’s a multiple single-segment TOP tolerancing..

SeasonLee