Following are the links to the previous blogs from this blog series:

• Smart 3D Modeling Blog Series: Designing a Variable Sized Ladder - Blog 1 of 4
• Smart 3D Modeling Blog Series: Designing a Variable Sized Ladder - Blog 2 of 4

Designing the Rung

You can create the rung outside and then place it between the side-rails or create it in-place between the side-rails.

1. Start the Place SmartLine tool to create a rectangular element on the inner face of one side-rails. (You can also use the Place Block tool, in which case most of the constraints will be taken care of automatically.)
2. Place the following constrains:
   1. Parallel constraints – between opposite edges.
   2. Perpendicular constraint – between any two adjacent edges.
   3. Distance constraint – the longer edge be constrained with Step_Size variable and the shorter edge be constrained with the Stair_THK variable.

1. Extrude the element up to the other side-rail. While extruding, constrain the Distance field with Stair_Span variable.
2. Constrain the bottom edge of the side-rail and upper edge of the step with First_Step_Rise distance constraint.
3. Constrain the bottom vertex of the side-rail and edge of the step with Step_Advance distance constraint.
4. Apply 3D Coincident constraint between the inner face of one of the side-rails and face of the step aligned to that side-rail

You now have a rung created with appropriate constraints defined. You can add additional details such as nut-bolt arrangement to connect the rung with the side-rail.

In the next blog, we will create an array of the rung.