Opinion on True Positions

[firehaus]

Hi All!!

I have an opinion question about true positions and look forward to everyone's feedback. We have one group that prefers to true position the hole with auto features, one point on the plane, four points inside the hole, then true position the hole. Now a second circle is added further into the hole, but not dimensioned and is used as a reference if there is a potential perpendicularity issue. The second group prefers to measure the hole with auto features, cylinder, three rows with five hits per row. No point(s) are taken on the surface and true position the cylinder as worse case on the axis. The part is either steel or aluminum about 1" thick with two machines/reamed .375 holes on either end of the part with the plane as the Datum -A-. Not going into to much detail on the part or GD&T as this is more about principal on true position accuracy.

If this was your part, how would you true position these features? Holes or cylinders? TIA

[dph51]

The TP extends the length of the feature.

Cylinder.

Fundamental Rule:

Unless otherwise specified, all dimensions and tolerances apply for full depth, length, and width of the feature.

[TheBradish]

^ What he said.

Although I can't speak from actual experience here. Most of our milling work consists of through-holes in relatively thin flanges. We measure them as circles.