What are Tetris shelves you ask? Remember the game Tetris? It has the seven different shapes that you stack together. Now imagine instead of blocks there are shelves in those shapes and you have Tetris shelves. A guy I know commissioned me to make some like the ones here at instructables. Most of the ones you see on the internet have no, or fixed shelves, at each of the squares. He wanted optional shelves. This complicates things a bit. He wanted each box to be 9.5″x9.5 square and 6.5″ deep. I thought 0.5″ MDF would be adequately strong without being excessively heavy. I chose MDF because he wanted to paint the shelves and it is cheaper than plywood. There are seven distinct blocks two of which are mirrored. There’s a left and right “L”, left and right “Z”, “T”, box, and line. He requested one of each.
First, I need a plan. I sketched out the shelves in CAD and worked out the dimensions so that all the pieces fit together despite orientation. Obviously, you don’t want gaps in between the pieces when they’re stacked together. For this you need the right size and 90 degree corners. I decided to use 0.5″x0.25″ rabbet joints with glue and brad nails on the corners. The use of brad nails meant I didn’t have to use a ton of corner clamps to hold everything while the glue set.
To start I picked up three sheets of 0.5″ MDF and ripped two of the sheets into 7″ strips. They’re 7″ because I wanted to use 0.5″ MDF for the backs of the blocsk too.
I used the CAD drawing to create a cut list and then cross cut all the pieces on the tablesaw.
I further divided the pieces into groups based on if they needed rabbet cuts at the edge or not. I used a stacked dado blade on the table saw to create the rabbets. The easiest way to size the rabbets is to set it close and then made some test passes adjusting as needed. MDF is a consistent thickness so once you have the size nailed in, you’re good to go for all the pieces. Here’s a pic cutting a test piece.
After lots of cuts all the parts have the rabbet cuts on the ends.
I wanted to use a 0.5″ thick MDF piece for the backs. A thick back piece will make the entire shelf ridged, strong, and keep the sides from bowing in. To fit the back, I cut more rabbets along the long edges of the pieces of each block. To make sure I cut correctly, I laid each block out and then cut the rabbets piece by piece going around the block.
A normal full kerf tablesaw blade is 1/8″ thick. A dado blade has two circular saw blades like you’ve probably seen in the stores and then additional chipper blades that are sandwiched in between. You can adjust the number of chipper blades (and shims too) to make your cut wider or smaller. These chipper blades have only a few teeth so they don’t bog the saw down. Unfortunately, using a dado blade doesn’t always leave a nice smooth cut. Sometimes you end up with ridges. Well, my set does. Maybe nicer sets don’t. No worry though because there are hand plane that can be used to clean up the surface. A pass or two and you have a nice flat rabbet. Yes, planes even work on MDF.
Here are the opposing “L”s laid out. To make the optional shelves I decided to use L brackets with 1/4″ pins. This required drilling 1/4” holes in the right spot. For the flat surfaces this was easy. Some of the pieces required drilling the holes at the corners though.
To drill the holes at the corners I glued and brad nailed the two pieces together and then took them to the drill press. Here’s a tip. Ideally all of my 7″ strips would be perfectly the same size. In truth though, since I don’t have a huge 16′ table to slide sheets of MDF along while cutting, there was a little wave in the cut meaning it wasn’t a consistent 7″. After you’ve cut the pieces there’s no way to add material back on though. To deal with this it is best to “hide” the problem. By “hide” I mean to put it some place where no one will see or care about it. For the shelves this meant making sure the front of the pieces lined up at the joints and letting the back vary a little bit. If you do this and the joint doesn’t match up perfectly on the back of the shelf no one will see it.
Once the two pieces were jointed I marked out and drilled the pin holes. These holes are dangerously close to the edge and would probably rip out at some point in the future. To fix this I’ll need to reinforce them. More on that later.
Now I can start building blocks by working around the them gluing and brad nailing the joints.
Once the sides for a block are all joined it’s time to cut out the back. This is pretty easy except for at an inside corner. Circular saw blades cut a little further on one side of the board than the other. If you go all the way to the line then you will have cut too far or not enough on the other side. To deal with this, you leave a little bit uncut and then come back with a hand saw and finish the cut.
Once the back is cut out, it is test fit and then glued and brad nailed in place. Here’s two of the “L”s with their backs in place.
This is a pic showing pieces stacking.
This is all seven pieces stacked up. The blocks aren’t glued to each other so you can reconfigure them whenever you want. Yes, I used an older sheet of MDF for the back of the T hence the different color.
In my next post I’ll cover my solutions for beefing up the corners with pin holes, how I messed that up, and then fixed it.