u/Typical-Priority1976
The writing on this show is second to none. I literally laughed out loud when Elliot said this.
u/Typical-Priority1976 — 4 days ago
Question regarding Datum Symbol Placement
In 6 . 3 . 2 . 1 (it kept trying to make it a link) where it talks about the placement of the Datum Feature Symbol, it says:
>(b) placed on an extension line of the feature outline clearly separated from the dimension line, when the datum feature is the surface itself.
However, it goes on in a later paragraph to say:
>(d) placed on the dimension line or an extension of the dimension line of a feature of size when the datum is an axis or center plane. (Figure 6.4, illustrations (a) through (c).
>(e) placed on the outline of a cylindrical feature surface or an extension line of the feature outline, separated from the size dimension, when the datum is an axis. (Figure 6.4, illustration (e) and (g).
In the images, all the examples show the Datum Feature Symbol in line with the dimension, but does it mean something different if it's not when the part is round? I am curious if there is a distinction.
In other words, in this first example, my understanding is that Datum A is the center plane of the part, and Datum B is the bottom surface (but I believe this is only correct because the part is square):
This is because 6.4 (b) says "placed on an extension line of the feature outline clearly separated from the dimension line" which makes the Datum "the surface itself", which Datum B in this case clearly is.
However, is that true when the part is round? In this scenario, there isn't really a surface for B to be (unless it's a tangent plane or something). I interpret this as "placed on the outline of a cylindrical feature surface or an extension line of the feature outline when the datum is an axis" and therefore, when I read this, I interpret Datum A and Datum B to be referencing the same thing in this instance; i.e. the center axis of this part.
This is because 6.4 (e) says "placed on the outline of a cylindrical feature surface or an extension line of the feature outline, separated from the size dimension, when the datum is an axis."
Basically, my question is this: In the screenshot above of the round part, does it mean the same thing if I do A or B?
u/Typical-Priority1976 — 15 days ago