Using only 2 datums to locate a hole.
Using only 2 datums to locate a hole.
(OP)
Hi All,
This is a very basic question, but just wanted to know all of your opinion on this.
Please see the attached drawing, the hole is located with only two datums. Like other cases it does not consider the bottom surface which is perpendicular to the hole axis.
I know this won't control the perpendicularity of the hole axis wrt to bottom surafce. Also this wont create a DRF.
1) Does this is legal representation in ASME Std??
2) Does it is always required to have 3 mutually perpendicular planes to establish a origion for measurement (Like DRF). if my functionality does not demands for perpendicularity of the hole can I use only 2 datums.?
3) In ISO std it is allowed to mention only 2 datums as shown in the drawing. but not sure wheter it is allowed in ASME, I have not seen new std ASME- 2009.
Could yu please clear this doubt?
This is a very basic question, but just wanted to know all of your opinion on this.
Please see the attached drawing, the hole is located with only two datums. Like other cases it does not consider the bottom surface which is perpendicular to the hole axis.
I know this won't control the perpendicularity of the hole axis wrt to bottom surafce. Also this wont create a DRF.
1) Does this is legal representation in ASME Std??
2) Does it is always required to have 3 mutually perpendicular planes to establish a origion for measurement (Like DRF). if my functionality does not demands for perpendicularity of the hole can I use only 2 datums.?
3) In ISO std it is allowed to mention only 2 datums as shown in the drawing. but not sure wheter it is allowed in ASME, I have not seen new std ASME- 2009.
Could yu please clear this doubt?





RE: Using only 2 datums to locate a hole.
RE: Using only 2 datums to locate a hole.
In my opinion this is legal, the other question is WHY? It is hard to imagine the design intent. Specifying location RFS also doesn't help. Just try to imagine fixturing of the part.
RE: Using only 2 datums to locate a hole.
John-Paul Belanger
Certified Sr. GD&T Professional
Geometric Learning Systems
RE: Using only 2 datums to locate a hole.
Frank
RE: Using only 2 datums to locate a hole.
...
(b) Dimensioning and tolerancing shall be complete so there is full understanding of the characteristics of each feature. ..."
The question then is whether the product definition is complete.
Jim Sykes, P.Eng, GDTP-S
Profile Services www.profileservices.ca
TecEase, Inc. www.tec-ease.com
RE: Using only 2 datums to locate a hole.
John-Paul Belanger
Certified Sr. GD&T Professional
Geometric Learning Systems
RE: Using only 2 datums to locate a hole.
Powerhound, GDTP T-0419
Engineering Technician
Inventor 2010
Mastercam X5
Smartcam 11.1
SSG, U.S. Army
Taji, Iraq OIF II
RE: Using only 2 datums to locate a hole.
Jim Sykes, P.Eng, GDTP-S
Profile Services www.profileservices.ca
TecEase, Inc. www.tec-ease.com