Thursday, August 22, 2013

Creating Parametric Kickers (Part 1)

This is an update to part 1 of the kicker exercise; we determined that mirroring or copying objects with void extrusions worked intermittently on different versions of Revit and using the default reference planes in the Generic Model template also caused problems.  Steps in red below are new and follow a course that should reduce any problems that you may have.

Curtain walls are designed to prevent water and air from entering a building but are, by definition, not load bearing or structural.  Whether in-filled with glass, metal panel, terra cotta, or other material, the curtain wall must be tied back to the building structure to maintain stability.  This is usually accomplished with anchors and, when additional stability is required, kickers are installed below the anchor then welded or bolted to a structural member.  A clear and informative definition and history of curtain wall can be found here and a set of common curtain wall industry definitions here. 

The design of this kicker will consist of a rectangular tube and two square plates as shown below.  Through holes at the front of the plates are for the bolts fastening the plates to the vertical mullions.  The slot at the back of the plates corresponds with a through hole on the horizontal member and allows for vertical movement of the plates under a load.  Shims, slip pads, fasteners and other hardware are not modeled in this exercise.   Small items, such as those, can slow down your computer's video capabilities, increase files size and are often better addressed in shop drawings rather than models.

Creating the parametric plates 

  1. Start by opening s new family using the Generic Model.rft template.
    • Make the Floor Plan view active then, in the Create>Datum panel, click the Reference Plan button. 

    • Create a new reference plane

    • Press Escape to end the command, click the new reference plane to select it, then rename it Plate_Inside_Ref in the Name parameter in the Properties panel.  This new reference plane will be the plane that the kicker plate is constructed on. 
  2. Open the Left view.
    • Click Create>Work Plane>Set.
    • In the Work Plane dialog box, click the Name radio button, expand the drop-down list and choose Plate_Inside_Ref.  This sets Plate_Inside_Ref as the active reference plane.  Click OK to close the dialog box. 

  3.  then click the Extrusion button in the Forms panel of the Create tab.
  4. In the Draw panel, click the Rectangle button, draw a rectangle near the origin then click Escape.

  1. In the Properties panel, set Extrusion Start to 0' 0" and Extrusion End to 3/8".  Click the Finish Edit Mode button (the green check mark) to create your extrusion,
  2. In the Left view, dimension the object as shown below.  The exact values do not matter, but the EQ dimensions do; they will ensure that the plates remain centered on the reference plane.

  1. Switch to the Front view, dimension the thickness of the plate, then align the left edge of the plate to the vertical reference plane.  Lock the alignment by clicking the lock icon.

  1. In the Left view, create another extrusion.  This time create a 1/2" diameter circle as the cross section, place it 1 1/4" from the front of the plate and 1 1/4" from the horizontal reference plane and lock those dimensions.  Be aware that the lock icons often appear a significant distance from the dimensions when creating extrusions.

  1. In the Properties panel, set Extrusion End to 2" and Solid/Void to Void.  This will create a circular hole in plates up to 2" thick.  Click the Finish Edit Mode button to complete the void extrusion.
  1. Repeat the void extrusion process to create another hole below the horizontal reference plane and then create a slot shaped void on the right side of the plate.  Remember to lock the dimensions and that the Solid/Void options defaults back to Solid each time.  Your extrusion dimensions will not be visible unless you are creating or editing the extrusion.

  1.   Test the model by selecting the plate and dragging the grips to resize it; the plate should change size, while the holes and slot remain in a fixed location relative to the reference planes.

  1.   Undo any changes then save the file.
  2. Next, we're going to add parameters to the model so that the dimensions can be adjusted numerically.  Select the overall horizontal length dimension then, in the Options bar, hold down the Label button and choose <Add Parameter>.

  1.   In the Parameter Properties dialog box that opens, make sure Family Parameter and Instance are selected then name the parameter Plate_Horizontal.  The Instance option allows you to define the length of the plate for different kickers throughout the model.  Click OK

  1.   In the Left view, the horizontal dimension is replaced with a parameter having the same value as the prior dimension.

  1.   Repeat the procedure for the vertical and thickness dimensions naming the parameters Plate_Vertical and Plate_Thickness respectively.

  1.   The vertical reference plane will represent the back of the vertical mullion and we want this to be 1/4" away from the vertical centerline of the plate.  We'll accomplish this by setting up a parameter that is mathematically tied to the horizontal length through a formula.  First, create a parameter for the dimension measuring the distance from the vertical reference plane to the front of the plate.  Name this parameter Plate_Mullion_Back and make it an instance parameter.

  1.   In the Modify tab of the Ribbon, click the Family Types button to open the Family Types dialog box.  In the Formula column for the Plate_Mullion_Back parameter, enter the formula: (Plate_Horizontal / 2)-1/4".   This moves the front of the plate away from the vertical reference plane a distance equal to half the plate length minus 1/4".  It is imperative that the referenced parameter is spelled correctly, including capitalization, or the formula will not work.  Revit will revise the units to correspond with the project standards.

  1.   Click OK.  The formula now drives the value of the parameter.  Save the file.

  1. To create the second plate, it should be as easy as mirroring or copying the existing plate to another location.  Revit, however, does not consistently work when mirroring void extrusions and using the Cut Geometry tool will create the cut, but eliminate the usability of the parameters and constraints applied to the plate.  If mirroring or copying the plate does not work properly, follow the previous steps, in the existing file, modifying them to create a second plate on the opposite side of the Center (Left/Right) reference plane.

As you can see, there were a few steps required to build the parametric plates, but it can be used in many configurations without the need to model a similar same object for every situation.  In our next post, we will conclude the exercise by creating the parametric tube and tying the objects together.