Good morning! I am very green to PC-DMIS and I need help. I have a part that has an ID -A- and ribs on the outside with slots cut into them. The width of the slots must be symmetrical to -A- within .010. I picked 1 point on each side of the slot and measured a cylinder around -A-. It is not working when I pick the two points alone. How do I properly dimension the symmetry callout? The part looks similar to the picture below. Thank you!
This symmetry callout is a bit confusing, as are most symmetry callouts. Hence why it was pulled from ASMEY14.5M in 2009 revision. Effectively, all that symmetry can control is perpendicularity of each slot width back to A. Create a mid-line perpendicular to Datum A for each slot. Measure symmetry to each line, back to A Datum Plane.
You could argue that it's implied to control polar rotation of the "4 places" orthogonality to each other, but that's ambiguous and ultimately up to the beer-holder (beholder).
If you want to pursue this interpretation, i'd construct two midplanes between the two mid-lines 180° apart, then I would construct an intersect line between the planes. I'd then dimension the perpendicularity of the intersect line to A, and measure angularity to 0.010 between the two planes (with 90° as nominal). Again, this is totally ambiguous interpretation, so maybe get guidance from engineer or customer on interpretation, prior to taking it to this level.
This symmetry callout is a bit confusing, as are most symmetry callouts. Hence why it was pulled from ASMEY14.5M in 2009 revision. Effectively, all that symmetry can control is perpendicularity of each slot width back to A. Create a mid-line perpendicular to Datum A for each slot. Measure symmetry to each line, back to A Datum Plane.
You could argue that it's implied to control polar rotation of the "4 places" orthogonality to each other, but that's ambiguous and ultimately up to the beer-holder (beholder).
If you want to pursue this interpretation, i'd construct two midplanes between the two mid-lines 180° apart, then I would construct an intersect line between the planes. I'd then dimension the perpendicularity of the intersect line to A, and measure angularity to 0.010 between the two planes (with 90° as nominal). Again, this is totally ambiguous interpretation, so maybe get guidance from engineer or customer on interpretation, prior to taking it to this level.
