I needed some new shelves but wanted to be able to disassemble/reconfigure/extend them if needed. As such, I built these three-plate shelves. They use press-fit finger joints so no screws or glue are needed to put them together, and the connections tessellate so the shelves can be extended up/across as needed.

Materials:
- 10mm thick MDF Sheet (sheet size depends on shelves required but 1.2m x 1.2m sheet will fit enough pieces for a 3-4 unit shelf)

Tools:
- CNC router or laser cutter
- Hammer

Step 1: Cut Shelf Pieces

The shelves are assembled from three repeated plates: riser (R), shelf (S), and back (B) pieces. Connections are friction finger joints which are divided between plates so that when four plates intersect (e.g. at an internal riser/shelf joint) there are no gaps or clashes. The attached dwgs are for a 10mm MDF sheet and create shelves with 180mm H x 230mm W x 240mm D internal shelf dimensions. To design your own shelves, first draw a finger joint (alternating squares) for a the particular material thickness you are using, and then divide the fingers between four intersecting plates (R/S/R/S intersection), and again for three intersecting plates (B/S/B and R/B/R connections).

Shelves.dxf
Download

Step 2: Orientate and Assemble

Arrange the three piece types as shown in the below picture. Then simply knock them together. If you use a hammer (i.e. not a mallet) use a scrap bit of timber to spread the load so the fingers don't split. If they do split, no worries, just keep hammering until everything straightens out again. The shelves should still be pretty strong.

Step 3: Expand

Repeat to expand the shelves as far as needed - just make sure the plates are aligned correctly (it is easy to tell if they aren't as certain finger joints will clash).

Step 4: Install

The connections should be strong enough to skip the occasional shelf / back piece (e.g. to access a power point behind the shelves). You could also coat / varnish the board but I liked the utilitarian look so left it as is.