Dimensional Measuring Interface
Standard
Standard Improvement Request
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SIR No. 97-56 DMIS Release 3.0 SIR Type Enhancement Severity Other Status Resolved Date Submitted August 13 1997 Date Validated August 13 1997 Date In Process Date Referred April 1 1998 Date Vote Pending August 20 1998 Date Closed August 20 1998 Action Clarifications Submitted By Thomas Kramer NIST Room B-124, Bldg. 220 Gaithersburg MD 20899 USA Phone: (301)975-3518 Fax: (301)990-9688 kramer@cme.nist.gov |
Problem Topic
DATSET: Reference to datums
Problem Description
Note: This is the first of four SIRs relating to DATSET on pages 113 and
114. I will also have several comments on DATSET on pages 17 - 19.
DATSET allows only three references to datums. This seems unnecessarily restrictive, since up to five datums might be used. For example, two lines could be used to establish the directions of the principal and secondary axes, and three points could be used to establish the coordinates of the origin.
References
None
Related SIRs
None
Suggested Resolution
Rethink DATSET and rewrite it.
To allow references to five datums, the input format of DATSET might be changed to:
D(label)=DATSET/var_1
Where: var_1 can be: MCS
or: var_2,var_3
var_2 can be: var_4,var_5
or: var_4,var_6
or: var_5,var_4
or: var_5,var_6
or: var_6,var_4
or: var_6,var_5
var_3 can be: XORIG,DAT(o1),YORIG,DAT(o2),ZORIG,DAT(o3)
var_4 can be: XDIR,DAT(d1)
or: -XDIR,DAT(d1)
var_5 can be: YDIR,DAT(d2)
or: -YDIR,DAT(d2)
var_6 can be: ZDIR,DAT(d3)
or: -ZDIR,DAT(d3)
The datums d1, d2, and d3 must be different from each other. The datums o1, o2, and o3 may be the same as each other (and may be the same as d1, d2, or d3) or may be different.
This intentionally does not allow for incompletely specified DATSETs.
Using this method, to specify a coordinate system from three planes, for example, the normal to one plane can be made the principal axis direction, and the normal to another plane can be used to establish the direction of the secondary axis. The point at the intersection of the three planes can be defined and used to set the origin.
This SIR has been referred to the Enhancements Subcommittee for resolution.
Support Documentation
None
Resolution
Warning!!
The following statement is only a resolution to a Standard Improvement Request (SIR) and is NOT part of the current DMIS standard, nor is it guaranteed to become part of the next revision of the DMIS standard even if voted and accepted by the DMIS National Standards Committee. This resolution is tentative because it may not be incorporated into the next version of the standard, it could be changed prior to the next release, or it could be changed as the result of the "public review and comment" period required for the next version of the standard. If you choose to use this tentative resolution, you do so at your own risk since at this time it is not part of the DMIS standard.
Rejected
This can be accomplished with two or more translates.
Furthermore, current tolerance standards (ASME Y14.5M) does not permit more than 3 datum features for a tolerance feature control frame.
Attachments
None
Notes
Added by Mike Holloway, hkm@ornl.gov on 7/31/1998
No reference was found to this SIR in any meeting minutes.
DATSET was meant to convey the association between datums on a part drawing (ANSI Y14.5) and the coordinate system used for measuring and locating the features. GD&T allows up to 3 datums to be defined (primary, secondary, and tertiary). The DATSET statement is there to associate the coordinate system axes and origin with the drawing datums. Do we want to break from this?