Casting Definition via GD&T
Casting Definition via GD&T
(OP)
I have questions regarding casting definition.
I will try and describe the issue and the questions without a picture or drawing. I think this will be ok.
I have a complex investment cast part/shape with primary/secondary/tertiary datums. Two lugs defined by a basic radius of .XXX establish the primary 'datum axis' E-F through the two lugs. A third lug defined by a basic radius of .XXX establishes the secondary datum G. A .250 diameter spot defined by basic X/Y dimension from one of the lug radii on a surface of one of the lugs establishes the tertiary datum H and constrains translation.
The engineering drawing consists of iso views which show the part and the datum structure with a note that states " Geometry defined by solid model XXXXXX-D-1 Rev X. Cast cores shall lie within a profile tolerance of .XXX relative to datums E-F, G and H. Other cast features shall lie within a profile of .060 relative to datums E-F, G and H.
My questions:
Can the cast datum lugs vary in size by the profile tolerance of .060?
The answer leads to this summary.
If I mount each part (I pick 20 for a sample) in a fixture which adequately locates on the lugs E, F, G and the point H (lugs E-F establish a datum axis E-F). I would expect any feature on the surface of all 20 parts to lie with profile of .060 relative to datum structure? This includes variation in datum size.
I will try and describe the issue and the questions without a picture or drawing. I think this will be ok.
I have a complex investment cast part/shape with primary/secondary/tertiary datums. Two lugs defined by a basic radius of .XXX establish the primary 'datum axis' E-F through the two lugs. A third lug defined by a basic radius of .XXX establishes the secondary datum G. A .250 diameter spot defined by basic X/Y dimension from one of the lug radii on a surface of one of the lugs establishes the tertiary datum H and constrains translation.
The engineering drawing consists of iso views which show the part and the datum structure with a note that states " Geometry defined by solid model XXXXXX-D-1 Rev X. Cast cores shall lie within a profile tolerance of .XXX relative to datums E-F, G and H. Other cast features shall lie within a profile of .060 relative to datums E-F, G and H.
My questions:
Can the cast datum lugs vary in size by the profile tolerance of .060?
The answer leads to this summary.
If I mount each part (I pick 20 for a sample) in a fixture which adequately locates on the lugs E, F, G and the point H (lugs E-F establish a datum axis E-F). I would expect any feature on the surface of all 20 parts to lie with profile of .060 relative to datum structure? This includes variation in datum size.





RE: Casting Definition via GD&T
You might want to look at datum targets that correspond with the nominal centers of the lugs or some such.
What is Engineering anyway: FAQ1088-1484: In layman terms, what is "engineering"?
RE: Casting Definition via GD&T
John-Paul Belanger
Certified Sr. GD&T Professional
Geometric Learning Systems
http://www.gdtseminars.com
RE: Casting Definition via GD&T
Jim Sykes, P.Eng, GDTP-S
Profile Services www.profileservices.ca
TecEase, Inc. www.tec-ease.com
RE: Casting Definition via GD&T
Mike Halloran
Pembroke Pines, FL, USA
RE: Casting Definition via GD&T
I provide an attachment to continue this discussion. I'm still looking for guidance/feedback.
I provide the original message text.
Two lugs defined by a basic radius of .450 establish the primary 'datum axis' E-F through the two lugs. A third lug defined by a basic radius of .500 establishes the secondary datum G. A .250 diameter spot defined by basic X/Y dimension from one of the lug radii on a surface of one of the lugs establishes the tertiary datum H and constrains translation.
The engineering drawing consists of iso views which show the part and the datum structure with a note that states " Geometry defined by solid model XXXXXX-D-1 Rev X. Cast cores shall lie within a profile tolerance of .XXX relative to datums E-F, G and H. Other cast features shall lie within a profile of .060 relative to datums E-F, G and H.
The part mounts to the next assembly via the mount lugs and surface H, which is why I chose datum axis E-F, G, and H.
My original questions:
Can the cast datum lugs vary in size by the profile tolerance of .060?
The answer leads to this summary.
If I mount each part (I pick 20 for a sample) in a fixture which adequately locates on the lugs E, F, G and the point H (lugs E-F establish a datum axis E-F). I would expect any feature on the surface of all 20 parts to lie with profile of .060 relative to datum structure? This includes variation in datum size. Each cast part must satisfy profile tolerance with variation in lug size.
RE: Casting Definition via GD&T
Is there an inherent advantage in choosing the large, flat surface on the bottom of the casting as the primary cast datum? I do machine this surface flat, therefore, I would loose the original cast datum.
Is a surface inherently advantageous as a primary datum (cast or machined) given a surface is not a "feature of size".
RE: Casting Definition via GD&T
It might be worth you looking at ASME Y14.8 to see how castings are dimensioned.
What is Engineering anyway: FAQ1088-1484: In layman terms, what is "engineering"?
RE: Casting Definition via GD&T
I provide attachment.
RE: Casting Definition via GD&T
Tunalover