One of the features that seemed most daunting to me when beginning, was the unique guards on the Pappenheimer with the holes inside them.
To create the initial guard, it was a matter of creating a dome, then flattening it and getting it into the general shape I wanted. Then I copied it and placed it underneath, and connected the edges to make a solid.
Off to the side, make a rectangle large enough to fit whatever pattern you’d like to “punch out” from the piece you just made. Then, on that rectangle draw out your pattern using circles, or any other shape you’d like to try. After drawing out your pattern, use the Push/Pull tool to raise it high enough so that it can go through and intersect your guard, while leaving the rectangle NOT intersecting the guard. Afterwards, make a group out of both this rectangle and the guard, so that you have two groups.
Move the rectangular group underneath the guard, but make sure the pattern is intersecting the guard. Then, select both groups, right click, and select Intersect Faces -> With Selection. This will create edges for you wherever geometry is intersecting. Afterwards, select both groups again, but this time select Explode. This will remove your groups and leave geometry.
Now, one by one, delete the pieces that were attached to the rectangle, and sticking through your guard. Afterwards, delete the face that was created from the outline of your pattern. Note that the inside is hollow. Delete the piece directly underneath it to create a clear hole. Select the internal faces that create the hole’s edge, and flip them to create a solid. Repeat this for the entire guard. There may be small areas where the intersection wasn’t 100% clean, but these are usually minor and can be fixed with a few lines.
Now just triple click your guard, and you are set to make a new group.