#Datum definition engineering full#
#Datum definition engineering iso#

The method is based on a constrained L2 (L2) minimization, which, when seen mathematically, elegantly combines the desirable contact properties of the constrained L1 (L1) minimization with the stable properties of the unconstrained least-squares and does so in a manner that avoids the drawbacks of either of those two definitions. This paper describes a completely self-balancing method for datum plane establishment that matches traditional surface plate mating while automatically stabilizing rocker conditions.

#Datum definition engineering iso#

We also show that the constrained least-squares solution has clear benefits over the shifted least squares solution.įor years (decades, in fact) a definition for datum planes has been sought by ASME and ISO standards writers that combines the contacting nature of traditional surface plate mating with a means of balancing rocking conditions when there is a centrally positioned extreme point or edge on the datum feature. Yet they also maintain close adherence to the maximum-inscribed solution when such solutions are stable. This datum definition maintains stability in cases where the maximum-inscribed fits are not unique and thus not stable. We demonstrate that the constrained least-squares is an excellent choice for several known problematic cases. With that success as motivation, we now investigate using this definition for circles, spheres, and cylinders.

#Datum definition engineering full#

The use of this definition for datum planes has already elegantly solved the problem of providing a full contact solution when that solution is stable, while providing a balanced, stable solution in the case of rocker conditions. This paper investigates a new datum definition based on a constrained least-squares criterion. However, we show this shifted least-squares solution has its own drawbacks.

For these problematic cases, many resort to using a least-squares fit whose diameter is scaled to be just inside (or just outside) the datum feature. Examples of these problem cases include cylindrical datum features having an hourglass shape, barrel shape, or the shape of a tapered shaft and circular or spherical datum features that are dimpled. The maximum-inscribed and minimum-circumscribed definitions that have often been used have known problems relating to stability in many common, industrial cases. For engineering drawings and CAD definitions, the problem of a suitable datum definition for datum features of circles, spheres, and cylinders has been sought by standards writers over decades.