|Re: Is this GD&T callout illegal?|
|Re: Is this GD&T callout illegal? -- Doug Bailey||Post Reply||Top of thread||Forum|
Posted by: John-Paul Belanger |
This is a legal callout, and is used to control the location of the holes only to each other. Whenever a pattern of holes is positioned, it automatically locks them in to one another -- no datum is needed for that; just the basic dimensions to tie them together. Other datums are often used to locate the holes from an edge or other feature. In this case, as Craig mentioned, the A datum provides the additional control of perpendicularity. But it does more than just perpendicularity: it controls hole-to-hole location (Craig -- it sounds like the other engineer you mentioned was missing that part, because you're right, why didn't they just use the perpendicular symbol if that's all they wanted!).The pattern as a group can then become a datum for something else on the print.
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