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-internal tapered radial slot

-internal round slot

-countersink

-internal spline

-woodruff keyseat

•A set of prismatic features might be,

•Macro Features,

-box

•External Features

-linear chamfer

-linear round

-linear v slot

-linear slot

-linear round slot

-linear t-slot

•Internal features

-rectangular pocket

-linear fillet

DQ:16.3 SOLID MODELERS

DO:16.4 MASS PROPERTIES

•A Numerical integration may be done on the geometry of a part by examining its components. From this mass, Polar and Cartesian moments of inertia, and centre of mass may be determined.

•An approximate division of space is often used called oct-trees. In this case the volume of the object is recursively broken down into finite parts. Other methods use an even division of space.

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• Is most successful with solids models.

DO:16.5 NON-MANIFOLD PARTS

•A manifold part makes sense mathematically. A non-manifold part may be interpreted in a number of ways, when dealing with general cases.

•Some examples below show manifold/non-manifold shapes

•Non-manifold parts have,

-vertices with less than 3 adjoining faces

-edges with more or less than two adjoining faces

-etc.

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•Non-manifold parts are required for,

-composite material modeling in a single part

-assembly modeling where parts touch or overlap (press fit)

-other Future Applications ????

DO:16.6 NUMERICAL ACCURACY

•Many CAD systems experience numerical problems based upon the nature of floating point arithmetic.

•This can result in points, and surfaces being distorted, and this may cause errors during comparison.

•To overcome the problem, most systems will allow a “point tolerance” value to be used to numerically compare, and join separated point.

A small numerical error results in a new edge

DO:16.7 PRACTICE PROBLEMS

1.Discuss the statement “Line trimming can be essential when constructing solid models”.

2.a) For the part below, describe how it would be represented with a winged edge B-Rep data structure. Draw the winged edges, then create data arrays.

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b) For the model in part a) suggest how tolerances could be added to the arrays.

3. Draw a B-rep solid model representation for the box below. Vertices have been drawn, you will need to add the other data elements to complete the model.

V4 V3

V7 V6

V8

V5

4.