Dowel holes alignment tolerancing/dimensioning

[vlg426]

I have two mating plates that need to be aligned using 2 dowl pins. Each plate has 2 H7 dowel holes and the dowel pins are m6. Datums are mating surfaces(A) and the sides(B&C). My question is in order for the plates to be properly aligned and assembled, the position of the feature must be within ?? diametrical tolerance zone relative to Datum ABC. Whats the value? How to decide/calculate?

Thank you

 

[KENAT]

You should be able to work it out from first principles but ASME Y14.5M-1994 appendix B actually walks you through it (you'll have to take into account that you have male pins not mating holes but shouldn't be too tricky). I once posted a excel with the calculations in it over in the GD&T forum.

To avoid overly tight tolerances I suggest keeping the protrusion of the dowel pins fairly short.

You might also want to consider if one of the mating holes can be slotted, this may help depending on your functional requirements.

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