Conical Datum Features

[drstrole]

If a conical tapered feature is a datum feature, do the angle and diameter(s) need to be defined with basic dimension, as opposed to a plus / minus angle angles and diameters? My thought is that it does because the datum feature simulator would collapse / expand as appropriate at the basic angle to contact the feature. That is how Figure 4-3(e) of Y14.5-2009 explains it in the chart, but there is not any further expansion that I can find to explain how simulation of the datum features happens in this case. With plus / minus tolerances on the angle and diameters how would you collapse / expand the datum feature simulator? Angle first, then diameter or vice-versa?

Drstrole

 

[powerhound]

I don't think you'll find a specific prohibition of using +/- tolerances on the angle of a conical datum feature but it doesn't make any sense unless the mating part is designed to conform to whatever angle the cone happens to be at. In that case, maybe a datum translation modifier is in order but that might be a stretch.

John Acosta, GDTP Senior Level
Manufacturing Engineering Tech

 

[greenimi]

http://www.geotolmeadows.com/newsletters/2009/nov2009.htm

Subject: Conical surface as datum

From Jim Meadows