A favorite of all Portal fans, the Weighted Companion Cube (or Companion Cube for short) is loved by all who enter Test Chamber 17 when presented with the lovable, pseudo-character as it provides comfort that no other being can provide; and now, you can make your own Companion Cube to provide you with all the comfort you could ever want!

This bite-sized 20cm³ box is great for storing all your valuable goods and doubles as a display piece as well, perfect for any Portal fan! This build is very simple to follow and requires only a few tools and materials to build, in fact, all the material I used was scrap! So without further ado, let's fire up the portal gun and jump in!

Step 1: Materials and Parts

Materials:

MDF Sheet (2ft X 2ft)
PVC Sheet/Styrene (4-5mm Plastic Sheet)
Superglue
Wood Glue
Pink Adhesive Vinyl (Optional)
Model/Squadron Putty (Air Drying)
Nails/Small Screws
Milliput (Epoxy Putty)
Painters Tape

Tools:
File Set (Flat, Half Round)
Sandpaper (120, 180, 400)
Scroll Saw (Or Any Wood Saw)
Utility Knife
Compass
Drill
Hammer

Paint:
Dark Grey Spray Paint
Light Grey Acrylic
Pink Acrylic
Emulsion Paint
Spray Primer

Step 2: Templates, Screenshots, Etc.

Listed above and below are screenshots references from the game itself and 2D templates (SVG, PDF and PNG) to aid you as much as possible with the build process. You can download both Letter and A4 versions of the PDF's to suit your printer and print at 100% scale. If you wish to edit the size, you'll have to tweak the scale to your specs.

Note; if you want to have the more accurate chunky corners, you'll need to double the thickness of the corner pieces to 12mm with these dimensions. I decided to go with low profile corners to make it easier to store and make it less cumbersome.

Step 3: Making the Base Box and Corners

Note: Unfortunately, my images of constructing the MDF box corrupted, so to make up for that I've provided a 3D gif to show how the pieces fit together. I used a jigsaw to cut out the flat pieces and then used wood glue and a combo of small screws and nails to assemble the base box. Lastly, I drew 2 centre lines (corner to corner) on every face to find the middle and marked it with a set punch; this will help with locating pieces later in the build.

The corner pieces are a little more tricky than the base box but we'll cover that in the next step. For all MDF parts, I'm using 6mm thick MDF.

The corner pieces are made up of 3 flat pieces of MDF which are labeled in the templates as corner "1", "2" and "3". These piece differ slightly as they have different edges and are assembled in a particular way to make up the final shape; You will need 8 of each piece.

I used a scroll saw to cut the outline and the 45° bevel (by tilting the scroll saw bed) to remove most of the material, using the templates as a guide; a scroll saw isn't necessary but it does make the process quicker. The edges were refined with files and sandpaper, then superglue is applied to the cut edges to harden and stiffen the raw MDF; this can be re-filed and sanded for a sharper, cleaner edge and surface, and it seals the MDF as a bonus.

Note: I'm using recycled MDF which had a coat of emulsion already applied to the surface, hence the pre-painted MDF.

Step 4: Corner Assembly

Before you assemble the corners, sand them first, it's easier to sand the inside curves before gluing them down.

When your pieces are nice and smooth, it's time to glue them to the box. To make sure you assemble them in the right order, I've provided another 3D gif (they're pretty fun to make XD) showing how they fit together.

The edges of corner "1" sit on the top of the lid and the bottom of the box and overlaps both "2" and "3" and corner "2" overlaps corner "3"; keep note of this to allow overlap so they match up properly! I pre-assembled every set corner on the box to see it's placement and traced the outline, this helps with gluing later.

To glue the pieces to the box, I used wood glue and a heavy object (a tool box in this case) as a weight to clamp them down.

The lid requires a little more setup. I set my lid flat and glued the pieces upside-down, making sure everything is lined up. Again, work your way around until all corners are complete.

The last thing to do is to file the lip on all "1" pieces as there is an intentional overhang. This is designed this way so you can file it down and fine tune the shape flush with the other corners.

Step 5: Box Refinement

Inevitably there will be gaps and imperfections between the corners. To fix this, Epoxy Putty (Milliput/Apoxie Sculpt, etc.) is used; it's easy to mix and easy to work with.

Epoxy Putty hardens after a set time (depending on the brand) and can be filed and sanded to a gloriously smooth state. Go over the whole box until all major gaps are filled. The putty can also be used to fix dents and small areas.

After applying putty and filing a couple times over, it's time to apply primer. Primer will be the base coat for paint but it also serves as an indicator and for smoothing the box. Spraying the box a solid colour brings out the mistakes and helps you see what extra work needs doing (pits and scratches are more visible, raised areas stand out more and so on.)

This time round we're using Modelling Putty (air drying) to fill the tiny areas that the Epoxy Clay missed. This stuff is far easier to sand and also leaves a really nice surface finish. Again, add primer after every pass with modelling putty and sanding until the box is perfect and ready for final paint.

Step 6: Discs

Before we paint, the box needs more pieces! We need 6 round pieces to sit in the centre on each face of the cube. I used recycled PVC sheet (MDF will also work) and a scroll saw to cut 6 circles. The edges were sanded to get them as circular as possible. (cutting circles is tricky by hand!) PVC sheet can also be cut with regular blades if you don't have access to any saws.

These discs are a different colour to the box, so they are painted a light grey (2-3 coats) and left to dry.

To tackle the most defining part of the cube (the hearts!) they can be painted pink with the use of a stencil or some masking work, however I wanted to use adhesive vinyl instead (the process a lot quicker and easier!)

Trace the heart shape (six times) on the back of the vinyl, cut with an x-acto knife (or even scissors!) and voilà! instant pretty hearts.

Carefully stick them in the centre of each disc (use a guide to line up the heart) and stick those suckers down! The vinyl is really vibrant, really durable and best of all, no brush strokes!

Step 7: Little Corner Pieces

I don't know what to call these little pieces so we'll just go with "extra little corners" XD

Like the discs, these are all over the box (12 in total) and are made in a similar fashion to the big corners. My choice of material is PVC again and my weapon of choice is a utility knife. A utility knife is strong enough to cut through the PVC so no need for saws!

Cut the pieces to the templates and glue them together at a 90° angle. Using a file, line up the pieces on a 90° edge (table counter works great) and knock the corner down. FIll in any seams and dents with Modelling Putty and sand down smooth.

Lastly, spray with primer and apply the same light grey paint used on the discs.

Step 8: Painting/Final Assembly

All the pieces are fabricated and ready, now it's time to paint!

The whole box needs to be dark grey; I opted for "Battleship Grey" spray paint by Ironlak and sprayed the box and lid with 2 coats.

The corners (like the other pieces) are a light grey so with care and patience, I hand painted the corners. You can use a light grey spray paint on the corners with masking around the whole box if you want.

One last feature on the cube are the pink lines. To do this, strips of painters tape are run along the box, leaving a 6mm gap for the paint. I applied 4 coats of pink to get a bold, streakless colour. Peel off the tape when the paint is dry and we are done painting! You could use vinyl for the same effect; totally up to you :)

Everything's in place, now it's time to finish! The little corners need gluing between each big corner and the discs need gluing in the centre. Using the pre marked centre on each face, we can draw a circle that's slap-bang in the middle of the box to help line up the disc. Superglue will hold up to the task just fine.

If you want the placement of the hearts in the correct order, I provided a flat layout showing where the hearts point. This isn't critical but it's there if you want it.

The final final thing to do is paint the inside and clear coat the box and lid to protect the paint job.

Step 9: Complete!

That's it! You're done! You can now keep all your favorite things safe, display the cube in its full splendor and acquire endless comfort from the almighty cube simultaneously!

You can store your valuable possessions, your secret plans of world domination, or store precisely 83.9 litres of water if you really really want; the list is endless!

I hope you enjoy this build and give it a shot, I always love to see what you guys come up with and if you reallly liked it, you can vote for the cube as well :)