I'd like to know how to connect the center of a polyhedron (e.g. a tetrahedron) to its four corners with cylinders (to be bonds), such as in the example below. Thanks!
Finally figured out how to do this! Not sure if it is the most efficient way but it worked for me. Here are the steps.
(a) Go to Edit>Preferences, and click on the Add-ons tab. Enable the Add Mesh: Extra Objects feature.
(b) Delete the default cube if you have it and add Mesh>Math function>Regular Solid. A tetrahedron should come up automatically. If not go to the Source pull down menu of the dialog box that came up when you first added the Regular Solid and change to Tetrahedron.
(c) The tetrahedron will be centered around the 3D cursor. Be sure not to move that cursor. Now add Mesh>Single Vert>Add Single Vert to add an a single isolated vertex at the 3D cursor.
(d) When you add the single vertex you will automatically be put in the Edit mode. So Tab back to the Object mode.
(e) Select the tetrahedron and the single vertex (in either order) and hit Ctrl J to join the two objects.
(f) Tab into edit mode, and select the wire frame view. Select the central vertex and one of the tetrahedron's vertices (in either order) and hit F. This should create an edge between the two vertices. Repeat the process three more times to connect the center of the tetrahedron to the other three corners.
(g) Select and delete the original edges of the tetrahedron. This should now leave four edges (lines) connecting the center of 3D cursor to the four vertices of the tetrahedron.
(h) Tab into Object mode, select the object and, from the Object pull down menu select Convert to > Curve from Mesh/Text.
(i) Click on the Object data properties tab and, under Geometry, adjust the bevel depth to the desired thickness.
(j) This gives the basic structure. Pull down the object menu and Convert to> Mesh from Curve/Meta/Surf/Text/. If you prefer you could add a Subdivision Surface modifier but in that case be sure to change from Catmull-Clark (default option) to Simple in order to retain the shape.