# 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