huangyhg

datum target areas
hello,
i am trying to use datum target areas to define primary datum a on a sheet metal part. i have some questions about datum target areas.
1. can i choose three non-co planar surfaces as my datum target areas?
2. can i and how do i dimension and tolerance the distance between those data target surfaces?
thanks a lot in advance.
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you can dimension between parallel, non-coplanar surfaces to create what is called a "stepped datum". the dimensions between are basic, with no tolerance. this would be applied by having a fixture that touches the part with posts at the various heights.
ye368,
first, do you have a copy of asme y14.5m? the spec goes into great detail how to define datum targets, the associated rules and possible applications. in general, datum targets designate specific points, lines or ares of contact on a part that are used in establishing a datum reference frame. these are located on a drawing with a datum target symbol.
datum target points - is indicated by the symbol "x" which is dimensionally (basic dimensions) located on a direct view of the surface.
datum target line - is indicated by the symbol "x" on an edge view of the surface, a phantom line on the direct view or both. the length of the line must be controlled, its length and location are dimensioned (basic dimensions)
datum target areas - where it is determined that an area or areas of flat contact is necessary to ssure estblishment of the datum. the diameter of circular area is given in the upper half of the datum target symbol.
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heckler
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yes - absolutely but make sure that manufacturing engineering agree with the target locations. design engineering should reflect the datums per assembly of the part while manufacturing engineering should decided the method of producing the part and their datum targets.
hope this helps.
dd
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