Family Composition

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SIMON DICKINSON: Hello.

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My name is Simon Dickinson.

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Let's now look at the composition of a Revit family.

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There are several features to be aware of when

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it comes to family composition.

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Reference planes, reference lines, constraints,

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and parameters.

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All families, regardless of type,

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are controlled using a skeleton, a series of references

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that we can control using dimensions.

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Geometries then attach and lock to the skeleton

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to make it parametric.

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Parameters should never be locked directly to geometry.

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This is generally regarded as bad practice

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and can lead to issues when geometries change later

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in the project.

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The first of the references is the reference planes.

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These have undefined end points, i.e.,

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They project indefinitely in both directions and once drawn

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can only be moved parallel to their created direction.

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We can name these planes, so that they

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can be referenced in views perpendicular

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to the created views.

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Let's look at the reference line.

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A reference line, unlike a reference plane,

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has defined start and end points.

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They also have four work planes associated to them--

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vertical, horizontal, and a plane at each end.

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Because each end is defined unlike with a reference plane,

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we can use angular dimensions to add rotational properties

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to it.

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Dimensions and constraints can be

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used to create how our skeleton moves and updates.

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Possibly the most useful constraint

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is the equality constraint that can

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be added to a multi dimension setting

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equally spaced references.

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We can then use this in conjunction

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with a dimension with a parameter assigned

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to it such as length.

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We can use the pin tool to constrain the direction

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the planes move when changed.

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Be careful not to overconstrain the model.

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Families such as beams are classed

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as two-point families defined in the project using

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a start and an end point.

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Notice that the structural beam template only has the length

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property defined.

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Notice that next to the length parameter,

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it is default in brackets.

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This indicates that length is an instance parameter.

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If we have set our structural properties correctly

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for the type of family we are creating,

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we can very quickly create dimensions

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and add the parameters to our references.

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Once we have created the references,

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we can look at creating our geometry.

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For beams, this is done using an extrusion.

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A basic one is already present in the template.

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We can edit this one to create any shaped beam we require.

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It is also possible to create geometry using blends,

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revolves, sweeps, and a swept blend,

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although these are not normally used

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when creating beam families.

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At any point, we can add additional parameters.

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Parameters can either be instance or type,

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remembering that's an instance parameter

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is unique to that instance of a family

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and a type parameter is unique to that family.

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Changing a type perimeter can change multiple instances

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at the same time.

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These parameters can also be a family parameter

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that only exists in the family.

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A shared parameter where the value

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can be used in a project schedule

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are important, a value that is not

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specified but driven by a dimension in the family model.

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These parameters can be used to control the family

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parametrically when used as a numerical value

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or as a standalone data such as manufacturer or product

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information.

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We can add families to our template.

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However, it is not good practice to have too many families, just

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a basic selection.

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Adding additional families to the project as

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required, remembering that each project will

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have different requirements.