Building a Spiral Staircase

Strictly speaking this is a helical staircase, not spiral, but it is possible to make a staircase that is both helical and spiral --- see QuadSpiral.lig. To construct a helix we use a rotation axis with constant radius and a Y increment for each step in the circle.

1.	Click on the New button to clear the decks for the new project.

2.	Click on the Y Rotation Axis button to obtain the Y Rotation Axis Dialog Box.

3.	Specify 20-steps making one 360° rotation (20-fold axis of rotation), but no Y increment.

4.	Enter a new vertex at X= 80, Y = 0, Z = 0. 20 new vertices are instantly generated.

5.	Enter a new vertex at X = 40, Y = 0, Z = 0. 20 more vertices are created.

6.	Click the Y Rotation Axis button again to remove the rotation axis.

7.	Starting from the X Axis, click on 5 vertices in an anticlockwise loop to create the bottom step face.

8.	Click on the Clean Up button to remove all lone vertices and renumber the attached ones.

9.	Clone the two vertices on the leading edge of the bottom step, moving them 25 units in Y with the up-arrow key.

10.	Create a 20-fold rotation axis again, this time with a Y increment of 10 units.

11.	Select the bottom step and two lone vertices. Click on Apply Symmetry to generate 20 steps and all handrail vertices.

12.	Select the 5 vertices needed to create a face for the bottom riser. 20 risers are generated.

13.	Select 5 outer vertices to make the lowest trapezoidal handrail face --- plus 19 instant replicates. Repeat for the inner handrail.

14.	To center the stairs on the origin, click on the Center on Origin button.

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This is a very basic spiral staircase. However you can easily add other features using helical symmetry and procedures similar to those above.