continuous feature and datums

[djhurayt]

A have a pin that I am struggling with the best way to control this thing. This is a precision pin with tolerances down in the single digit micron level.

1) In the attached image (upper one), does my use of "3X", "CF" and the dimension for the fourth feature of the same size diameter properly show that the three diameters to the left are to be treated as one feature and that the fourth diameter is its own entity?

2) Is it then implied that when location on datum A to find the relative position of the other end, that all three of these surfaces need to be held by the collet/chuck/holding fixture?

Or is something like in the lower part of the image, and controlling E to a datum C-D be a better idea?

Ultimately the three surface of the left end have to fit into a slip fit precision hole and the other end needs to be concentric to the axis of these three surfaces.

 

[pylfrm]

djhurayt,

1) Although the text doesn't say one way or another, the figures in ASME Y14.5-2009 do not show a quantity when the <CF> modifier is used. I'd remove the "3X". The separate dimension on the fourth feature should make the intent clear.

2) Datum feature A would include all three surfaces. I think it would be more clear if the dimension line (and associated datum feature symbol) weren't inside the part outline though.

Based on your description, the continuous feature approach is probably the better idea of the two.


pylfrm