I typed in 'osnap' to get the Object snap options and turned all of them on. These drawing aids are highly useful.
I drew two circles and imposed 'Parametric>Geometric constraints>Concentric' on them.
With the rectangle tool, I drew a rectangle between the two circles.
I zoomed by scrolling the mouse to check the intersection of the rectangle with the two circles. The edges had extended into the circle.
By using the 'Trim' tool and selecting the rectangle, I could trim away the portions that extended beyond edges.
I used the 'Polar array' tool to generate 6 rectangles to fill the 360 degrees space. It felt so good to do this and save a lot of time!
I zoomed in and trimmed off the edges that were intersecting.
I used the 'Region' tool to fill in the shape with some area. I could then do Modify>Solid editing>Subtract to subtract the triangular regions from the whole.
I chose the circle in the centre and did 'Union' of it with the whole.
I typed in 'ext' in the command line to extrude the 2D design into a 3D model.
I wanted a rim along the edges to fit this structure inside the Big Mack. While I was wondering how to do this, our instructor could solve it easily. We drew a rectangle with the dimensions equalling the thickness and height respectively of the circular edge. I drew an arc inside this rectangle and trimmed away some edges.
We rotated the arc 360 degrees after specifying the start and end points of the Z axis. A simple 'Difference' of this new structure from the whole could finally give me this design that I wanted. What a high! :D