# Modeling a bipyramidal shape

I need to draw some bipyramidal shape in Blender (for a nanohub simulation) but I am completely new to this field.

Can anyone help me understand how to model such shape?

• Can you elaborate with an illustration of a "bi-pyramidal shape for nanohub simulation" in question.(and or links) – batFINGER Dec 27 '18 at 11:58
• nanohub.org/tools/ddaplus/session?sess=1430872 – Rithesh Raj Dec 28 '18 at 6:29
• Link above requires registering / logging on. Can you add a screenshot? – batFINGER Dec 28 '18 at 6:36

1. Create the bi-pyramid's base.

If the base is going to be a regular polygon, just do: Add > Circle, then look for this menu to change the number of vertices. The menu is obtained using F6 in Blender <2.79, or you can just find it in the bottom-left of the Viewport in Blender2.8+

2. Jump into Edit Mode (Tab). Select all the vertices (A), then Extrude upwards in the Z direction (E then Z). If you hold Ctrl after starting the extrusion, you can do it by snapping to fixed increments.

3. Deselect the top vertices, select the bottom vertices (I used the B Box Select tool), and Extrude them downwards

4. For both the top and bottom ends: select them, then scale to zero: S, 0, Enter

5. To finish, select all the vertices (A), then do Remove Double Vertices from the right mouse button menu (Blender 2.8+) or from the W button menu (<2.79)

The mesh is already done after step 4, but step 5 gets rid of redundant geometry and open surfaces (which is a requirement for many operations, including boolean, subsurface, 3D printing).

For a general Bi-pyramid ...(working in XY, Z up)

1. Create a circle with the requisite number of sides, and a triangle fan fill.
2. Assign a Mirror modifier in Z, (no clipping or merge at this stage)
3. GZ Move the central vertex in Z

At the creation stage, you can enter the radius numerically, and GZ + (a number) lets you set the height/2.

Now you can switch on 'Merge' in the modifier, before applying it, if you want to.