Tapered Datums

[AMontembeault]

Y14.5 specifies the use of a conical taper as a datum candidate, arresting 5 degrees of freedom - 3 translational, 2 rotational. It makes me wonder, why couldn't the same apply to a wedge shaped, extruded feature - a dovetail, for example. Such a feature would also constrain 5 degrees of freedom, 2 translational, 3 rotational. Y14.5 doesn't explicitly call out such a feature, so I'm left questioning if this is indeed applicable as a logical extension that's just overlooked in the standard, or if I'm missing something that makes this impossible.

 

[mfgenggear]

Y14.5 specifies the use of a conical taper as a datum candidate, arresting 5 degrees of freedom - 3 translational, 2 rotational. It makes me wonder, why couldn't the same apply to a wedge shaped, extruded feature - a dovetail, for example. Such a feature would also constrain 5 degrees of freedom, 2 translational, 3 rotational. Y14.5 doesn't explicitly call out such a feature, so I'm left questioning if this is indeed applicable as a logical extension that's just overlooked in the standard, or if I'm missing something that makes this impossible.

Good question. And it brought out past issues as you stated. I will defer on this as far as the merits of ASME. But when it was difficult to measure a taper, but it was normally a gage point. I would draw in cad the actual geometry. And calculate the theoretical sharp internal or external edges or internal corners. And add a reference dimension or diameter. While this doesn't answer your question directly. Point is I would do work a rounds. As you stated conical I normally would design a gage with sharp corners for internal or use spherical ball that would contact at the exact
Gage point.

 

[Burunduk]

It is the same type of datum feature as "Linear Extruded Shape". Look that up in your copy of Y14.5.

 

[AMontembeault]

It is the same type of datum feature as "Linear Extruded Shape". Look that up in your copy of Y14.5.

Derp! Got it, thanks!