Datum Feature Symbol placement
Datum Feature Symbol placement
(OP)
I have searched through my GD&T books and have come up short on certain situations. All per ASME Y14.5M-1994.
1) Datum Center Plane (see http://i18.tinypic.com/68j3ode.jpg )
I know that datum B would be valid in defining the center plane datum from the .325 dimension. But does datum A also work in this same instance?
2) Datum Axis (see http://i10.tinypic.com/6cyanif.jpg)
For the shown shaft, I know that Datum C is correct. But would datum A,B also be correct?
I know if you are looking at the ends of the shaft, you can define a datum by placing it on the circle of the shaft. Which makes me believe that A would also be valid because you have a center-line defining that the object is cylindrical.
I am still fairly new to GD&T so any help would be appreciated.
1) Datum Center Plane (see http://i18.tinypic.com/68j3ode.jpg )
I know that datum B would be valid in defining the center plane datum from the .325 dimension. But does datum A also work in this same instance?
2) Datum Axis (see http://i10.tinypic.com/6cyanif.jpg)
For the shown shaft, I know that Datum C is correct. But would datum A,B also be correct?
I know if you are looking at the ends of the shaft, you can define a datum by placing it on the circle of the shaft. Which makes me believe that A would also be valid because you have a center-line defining that the object is cylindrical.
I am still fairly new to GD&T so any help would be appreciated.





RE: Datum Feature Symbol placement
1: Your assumptions are correct.
2: Only Datum A & B can be used as a datum axis. Datum C would be interpereted to be the outside surface of the shaft.
I looked this up in a book and referenced a few files of mine. A few years ago my GD&T checker and I had an argument about a situation similar to #2. I thought that datum C could also be a datum axis, however after many wasted hours of arguing I conceeded that he was the expert and it was not.
hope this helps.
RE: Datum Feature Symbol placement
As far as refering to the outside surface of the shaft as a datum, this is still correct. The surface would be the datum feature and the centerline would be the datum axis (of that feature). Datum axis' are extensively used but you don't call out the axis (centerline) as a datum.
I know others will feel free to correct me if I'm wrong.
RE: Datum Feature Symbol placement
Powerhound
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RE: Datum Feature Symbol placement
Marcelino Vigil
GDTP T-0377
RE: Datum Feature Symbol placement
RE: Datum Feature Symbol placement
In addition to the GD&T:
Outside machining, arrows on outside; inside mach, arrows on inside; Holes, arrows on inside or point to hole.
Can be the same for GD&T symbols.
This reduces second guessing by machinists as is more clear.
This is my drafting practice for past twenty years and vendors/machinists like it.
Chris
SolidWorks 07 4.0/PDMWorks 07
AutoCAD 06
ctopher's home (updated 04-21-07)
RE: Datum Feature Symbol placement
see axis_as_datum http://tinypic.com/625sq6s.gif
see center_plane_as_datum http://tinypic.com/6g9if7l.gif
RE: Datum Feature Symbol placement
-- placed on the outline of a feature surface, or on an extension line of the feature outline, clearly separated from the dimension line, when the datum feature is the surface itself.
-- placed on an extension of the dimension line of a feature of size when the datum is the axis or center plane.
-- 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 the axis.
-- placed on a dimension leader line to the feature size dimension where no geometrical tolerance and feature control frame are used.
-- placed on the planese stablishedb by datum targets on complex or irregular datum features ....
-- placed above or below and attached to the feature control frame when the feature (or group of features) controlled is the datum axis or datum center plane.
GDT_GUY