Good news! The base is already constructed. 2′x2′ MDF at 3/4″ thickness makes a solid base.
The next step is to fix the base to the beam. I would recommend five attachment points – two on each end beam and one in the middle, to create an X pattern like what you would see on a 5-of-diamonds.
Place the beam on top of the base and mark its outline. Figure out the hole locations in the beam and mark them on the beam and the base. Drill cleanly through the base and then separately, drill into the beam. (I find drilling separately is just easier than drilling blindly through both elements together. But if you are not geometrically inclined then feel free to do it your way.) Line up the holes and screw in your screws. The longer the screw the better, but I would advise less than 5″ so you don’t have interference problems when you attach your L-braces later.
You can also attach L-braces between the base and beam to increase the joint stability but to be quite honest I forgot to do this. It has not affected the reliability of the tree one bit, so I won’t cover it here.
Do the same thing with the box. Attach it to the top end of the beam using the same 5-of-diamonds attachment pattern. I did remember to attach L-braces between the box and the beam on the outside. You need no more than four medium-sized ones (6″ long on one side); attach two each on the heavier sides of the box (those with closed walls). This will ensure a stable box.
The last construction step is to attach the shelves. One of our shelves is oriented long-ways and one is oriented side-ways. Fix two large (we used 12″ x 10″) L-braces to the shelves and then fix the other end of the L-braces to the beam. This part will be slightly painful because if you orient the shelves the way we did, one of them is going to have issues. Try to avoid placing the L-brace holes on the gaps between the 2×4’s in the beam. I left the lower holes of the L-braces (circled) unused and went for a secure connection on the top holes. Just to be safe make that the lower shelf, so if it fails (again, I have not yet observed anything close to a failure) the drop distance is shorter.
As you can imagine, carpeting the structure is relatively straightforward. You will need to ensure some degree of overlap. Especially while wrapping the beam, watch out for the added diameter due to the L-braces. Nail the carpet to the tree structure every 6-8″. If you picked the right carpet your cats will shred this thing until the carpeting falls off, so make it last by securing the carpet with nails. Small round nails are best to avoid hurting kitty’s claws. DO NOT use staples, as they can easily catch a cat claw.
Use frequently.
