Datum Pattern Dimensioning
Datum Pattern Dimensioning
(OP)
When you have a pattern of holes as a datum, do the dimensions for other features come from the centerplane derived from the pattern, or from the center of one of the holes? I've been searching around and I keep finding it done both ways, are both ways really allowed? I believe inspection is done by establishing the centerplane, so I'm inclined to assume that dimensioning to the centerplane is the way to go.





RE: Datum Pattern Dimensioning
If inspection is going to establish center plane(s) then dimensioning from that might save a little math but that's about it.
It's a bit like when you locate a hole pattern from an edge. You can either go from the edge to each hole, or from the edge to the first hole, then from that hole to the next etc. The schemes have advantages & disadvantages in different stages of the design & manufacturing process.
KENAT,
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RE: Datum Pattern Dimensioning
RE: Datum Pattern Dimensioning
This is related to the often-discussed issue of where the "datum axis" or "datum center planes" or "origin" of a pattern of holes is. To me, it is arbitrary - the designer can pick a particular origin or let the inspector pick one. As KENAT said, different schemes have advantages and disadvantages to different users of the drawing. But functionally they are all identical.
Evan Janeshewski
Axymetrix Quality Engineering Inc.
www.axymetrix.ca