1MAE 455 Computer-Aided Design and DraftingDatum Geometry & Engineering FeaturesAs well as: Primitives, Boolean Operations & Design IntentMAE 455 Computer-Aided Design and DraftingDatum GeometryDatum geometry is points, curves, and sur-faces that are used as reference to help the designer define locations and orientations for the placement of features.In NX there are three types :1)2)3)22MAE 455 Computer-Aided Design and DraftingDatum GeometryAs well, any point, curve or surface that is not part of a solid can be used as a datum – as long as it does not disappear in later modeling operations.For example:••3MAE 455 Computer-Aided Design and DraftingWhy use Datum Geometry?• Some shapes can only be created using datumgeometry.• Building on datum geometry is safer than building on solid geometry. Design changes can cause solid objects (faces, edges, points) to actually disappear!! Datum geometry will always be there for you!• Building on datum geometry is more flexible. You can re-order the sequence of features more easily since there are fewer dependencies between features.43MAE 455 Computer-Aided Design and DraftingDatum PlanesCan be used to:– Provide a planar location for a sketch– Position engineering features– Provide a trimming objectThere are two types:1. Fixed Datum Plane– Created automatically when starting a part.– Created by typing in coordinate parameters.– Use ONLY to start the part.5MAE 455 Computer-Aided Design and DraftingDatum Planes2. Relative Datum Plane– Use them extensively while creating parts. – Can be moved by adjusting parameters or dependent geometry– Various construction methods are available:••••– Only build on other datum if you can.64MAE 455 Computer-Aided Design and DraftingDatum AxesCan be used to help create:– datum planes– revolved features– extruded featuresLike datum planes, there are two types:1. Fixed Datum Axis– Created automatically when starting a part.– Created by typing in coordinate parameters.– Should be used only to start the part.7MAE 455 Computer-Aided Design and DraftingDatum Axes2. Relative Datum Plane– Use them extensively while creating parts.– Can be moved by adjusting parameters or dependent geometry– Various construction methods are available:•••– Only build on other datum if you can. 85MAE 455 Computer-Aided Design and DraftingDatum Coordinate Systems• Can be used to automatically create a set of orthogonal datum planes and axes• There are two types:1. Fixed (Absolute) Datum Coordinate Sys.2. Relative Datum Coordinate System• Automatically include:– Origin point for the coordinate system– X, Y, & Z datum axes– XY, YZ, & ZX datum planes9MAE 455 Computer-Aided Design and DraftingEngineering Features“Engineering Features” automate the construction of shapes commonly used in mechanical engineering:– Boss– Slot– Pocket– Hole(What are other ways of creating these solid shapes?)106MAE 455 Computer-Aided Design and DraftingEngineering FeaturesCreating an engineering feature involves:1) Specifying the feature parameters2) Specifying the position of the featureThe idea is that they save you time. How?It is also possible to create your own “user-defined” features.11MAE 455 Computer-Aided Design and DraftingPrimitives• Primitives are basic geometric solids– Block– Cylinder– Cone– Sphere• Not commonly used.• Can be created:1.in place (fixed)2.with reference to other geometry (associative).• Always create primitives associatively!127MAE 455 Computer-Aided Design and DraftingBoolean Operations in NX• Use Insert  Combine Bodies  Unite / Subtract / Intersect• When creating solid shapes (by sweeping or primitives), use the “Create” option, then create Boolean operations separately. This makes the shapes more independent, since you can just delete the Boolean operation and the two shapes will remain.(What is another way features can be made more independent?)13MAE 455 Computer-Aided Design and DraftingA Note on Design Intent• Yes, it does matter how you create a solid, even if the results look the same!• “Design Intent” is the rationale behind why you made the part the way you did. Shapes on a part are there to enable some functionality or fulfill some requirement. • Your modeling approach, the sequence of features you choose, must reflect your design intent.148MAE 455 Computer-Aided Design and DraftingA Note on Design Intent• Your model should satisfy the following criteria:1. Try for 1-1 mapping between design intent & feature. Each feature should embody one function or requirement. Each function or requirement should be embodied by one feature.2. All important dimensions must appear explicitly. If “wall thickness” is an important design parameter, it should appear in Tool  Expressions.3. Minimize the number of parameters.4. Minimize the number of