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# Parametric Modelling Strategies

• A sketch is made up of three parts; sketch entities, geometric relations and sketch dimensions. The optimum way to create a fully defined sketch is to first draw the sketch geometry capturing automatic relations, then add in any required extra sketch relations and finally dimension the sketch.
• Build design intent into sketch geometry as you proceed by using appropriate tools such as horizontal, vertical, tangent arcs, axes of symmetry and coincidence to automatically capture relationships.
• By exaggerating sketch geometry initially and then using dimensions and constraints to refine and control it, correct design intent will be realised.
• Select the best (most descriptive) profile for the model base part and sketch this on the corresponding sketch plane to maintain model orientation.
• Use symmetry in both the sketch and in the extrusion to place the model origin in the centre of the model where parts are symmetrical in two directions.
• For rotational parts place the origin on the axis of symmetry to make the additional of subsequent features easier.
• Avoid dimensioning, constraining or extruding geometry to fixed values if that does not reflect the design intent.
• Create important part features as high up the design tree as possible to permit maximum design flexibility.
• For thin walled parts complete one side of the material and use the shell tool to automatically take care of the other side.
• Apply cosmetic fillets and chamfers as the last model features where feasible.
• Use the correct end condition type to reflect the design intent. For instance, if a hole is to always go through a part, then use the through all end condition so that the hole will still go through if the design is increased in size along the axis of the hole.
• Add draft features before fillets.
• Add larger fillets before smaller ones.
• Where rounds have the same dimension, use a single fillet operation to round several edges at the same time. This results in a more efficient model and a shorter design tree.
• As a rule of thumb avoid having more than ten entities in a sketch unless absolutely necessary. It is usually easier and better to have less complicated sketches and more features.
• Use open and closed profiles appropriately.
• Sketch in 2D and 3D. Sketching usually takes place in 2D, but by slightly rotating the model to give a 3D view after starting, it is often easier to see where one is sketching and to select the correct model references.
University of Limerick

Department of Manufacturing
and Operations Engineering