Now create another box but this one crosses the ones you just made. Chamfer it to sharpen it's edges.
Now make an array of six of them (Tools->Array...). The picture shows the settings I used but you will probably have to experiment to get settings that work right for you.
So that we don't have a lot of separate pieces, we are going to attach all the bars into one piece of geometry. Select the first of the vertical bars and hit the "Attach" button and then select the other bars. Every time you select a bar, it will be attached. When all six are part of the same geometry, add a symmetry and meshsmooth.
When everything is smoothed, it should look like the picture.