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Solid versus Void

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In this article we are going to take a look at the basic geometry that makes up any components- specifically Solids and Voids


In this article we looked at how every component is made up from a number of individual mass geometry. We also said that there are four different methods for creating this elemental geometry.


In this article we are going to look at each of the four methods in turn. In doing so, we will look at the basic method of using each tool and also explain when it would be appropriate to use them.




Solid Extrusion


Extrude is the simplest of the four Solid Form Creation Methods. The use of this tool requires two distinct steps.


Sketch the profile that you wish to extrude.



Set the Depth for the extrusion. Note: You can also set the absolute Start and End for the extrusion.



Selecting Finish Sketch, tells Revit to go ahead and create the geometry based on the profile and extrusion depth settings we have made….




Extrusions have the same profile over the entire of their length

The Profile can only be extruded perpendicular to the plane in which it was drawn.

Sketching closed loops within the overall profile we define, will result in voids being created in the extrusion- see below


Sketching this profile…



Produces this extrusion….




Solid Sweep


Along with Extrude, the Sweep tool will be used to create 95% of the geometry you need for your components.


Using the Sweep tool is a two step process. First of all we need to draw a 2D path along which our profile will be swept. Note: The 2D path does NOT need to be closed. If we want to create a picture frame, we would wish for a rectangular path….



Note: The 2D path is shown in pink. It is a closed rectangular loop because we wish to create a rectangular picture frame.


Now for the second step: We need to draw a 2D profile- ie we need to define the shape that we want to extrude (if you like) along our path. For our picture frame, we need to sketch an appropriate moulding for the cross-section of timber….



Selecting Finish Sweep results in…..



Below is a close-up of the frame, so you can see how the profile we sketched has been “swept” along the path we defined. NOTE: I have taken a segment out of the path (and consequently the finished sweep) to allow you to see the cross section of the geometry we have created. It also highlights the fact that your 2D path does not need to be a closed loop.




Solid Revolve


The next tool that we are going to look at is the Solid Revolve. This tool is allows you to define a profile and then revolve this 2D shape around a central axis, to form a 3D mass. Examples of when you may need to use this tool are:


  • Creating a domed roof

  • Creating a door knob


Once again, the use of this tool takes a two step approach. With this particular tool, either step may be performed before the other.


So let’s start by drawing our profile. The profile must take the form of a closed loop.

Now we have defined our profile, let’s define an axis about which we will revolve the profile. We define the axis simply by drawing a line….



The axis is the blue line in the image above. Note: The axis can be drawn to any length- The only constraint is that it is drawn in the same plane as the profile.


All we need to do now is select Finish Sketch and let Revit produce the solid geometry…



And there it is, in all it’s 3D glory! The default angle for revolving our profile around the axis is 360 degrees- but we can change that value to an angle less than 360. Let’s change the end angle to 270 from the start angle.



Our geometry is modified accordingly……



This allows us to clearly see the shape of the profile that has been revolved around the axis.



Solid Blend


Now to the last of the four Solid Form creation tools: Solid Blend. Quite simply, this tool works in the following manner:-


· Draw a shape to define a Base profile

· Draw a shape to define the Top Profile- this shape does not have to have any relationship to the one used for the Base Profile.

· Specify the relative distance between the two profiles

· Let Revit blend (or morph’) one profile into the other over the distance between them.


It is probably easier understanding this tool by use of a graphical example…


Let’s draw a base profile. For our Base we draw a square (approximately!)



And now let’s draw the Top Profile. We will draw a simple polygon….



And now we will tell Revit the distance between the two profiles- we’ll set this at 800….



Selecting “Finish Sketch” let’s Revit produce the following geometry..



You can see how Revit has morphed the Base Profile into the Top Profile, over the 800mm distance that we specified.



Summary and conclusion


In this article we have looked at the four methods of creating primary Solid Forms. Void Forms work in exactly the same way and have the same four tools…



Through the use of these tools it is possible to create (virtually) any three dimensional geometry that you can imagine. Obviously we have used very basic, non-parametric examples to help convey how these tools are used and what they produce. In future articles we will look at how Reference Planes and Parameters allows us to create “dynamic” geometry that can be modified “on the fly”, within a project.

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