Best practice to establish datums on injection molded part of which every all are drafted

[Shatawa]

Usually we pick surfaces that are mutually perpendicular to each other as datum planes. What's the best practice to pick datum planes if all of the surfaces of the part is drafted and there are no surfaces perpendicular to each other ?

 

[3DDave]

Are there any mating surfaces? Are there places with ejector pin marks?

It is difficult to give a general purpose answer to an infinite range question.

 

[Shatawa]

yes, there are mating surfaces. Mating surfaces and ejector pin mark places. I intended to specify the largest mating surface as datum A plane. Datum B and C will then be 88 deg with respect to A.

 

[3DDave]

Those are probably fine (considering I have no idea what shape the part is). Inclined datum features are supported; the datums themselves are considered to start from the intersection of the secondary and tertiary features with each other and the primary feature.

 

[SDETERS]

A couple of things we do, if possible have your datums on one side of the tool, do not have your datums cross the parting line. Also, look into using datum target points. Is there one surface that is "flat" on this part, or mates with another part? Do you have any cone or cores in this part?

 

[Eric Gushiken]

Datums can also be lines (edges) and points so you could use the edge along the wider side of the draft as a secondary datum. If symmetry was important you could pick both edges on the wider side as secondary datum B-C.

 

[Burunduk]

Datums can also be lines (edges) and points

Datum lines are supposed to be center axes of surfaces of revolution such as cylinders and cones. The intent of the inclusion of "line" in the datum definition is not the usage of edge corners as datum features. Another datum-related "line" is a datum target line, but that is typically the result of a tangent contact between a planar feature and the periphery of a cylindrical datum feature simulator or vice versa. Functionally, datum features are the surfaces on which the part is mounted.

 

[Eric Gushiken]

Datum target lines don't have to be related to cylindrical features. Using the sharp edges as a secondary datum is perfect for the Ops scenario where there are no perpendicular surfaces. Just lay the bottom flat surface on either the mill table or inspection table and use either an edge finder or inspection probe to pick up the edges.

 

[Burunduk]

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