As a dad of 3 years old kid, I play Lego Duplo often. And I got disappointed a bit when I realized that there is no original baseplate wider than 8x8 pins. 8x8 pins plate allows set up 4x4 bricks only. It seems too small for really big projects.

I present this way how to make a baseplate for Lego Duplo as large as you want. It is an easy-to-make and environment-friendly project.

The idea is very simple: to make a set of holes with the shape of Lego Duplo bricks.

Step 1: Tools & Materials

Tools:

Pencil
Eraser
Ruler
Sarp-blae knife
Cutting mat
Some Lego Duplo bricks as a measure

Materials:

Cardboard
Double layer cardboard (look at the picture). If you have no a piece of double layer cardboard, you may glue two pieces of one layer cardboard by PVA glue.
PVA glue

Step 2: Drawing a Grid

First, you will need to draw a grid on a piece of double layer cardboard. Each square of this grid should be equal to a Lego Duplo Brick (1.25"=31.8 mm). You may use a Brick as a measure.

Also, you need to add 1/2 of a Brick size (0.63"=15.9 mm) space between a cardboard edge and the grid.

I have made an 8x7 grid, but you can do your baseplate as much as you want.

Step 3: Checking

As you have finished the grid, check each square of the grid by some Lego bricks. You should be sure of each square before start cutting.

Mark what squares you want to cut. You may cut one-square holes, as well as two-square holes.

Keep in mind that it should be some space between holes; otherwise, it would be too flimsy.

Step 4: Cutting

You will need to cut out holes you have marked.

You may check holes by Lego Duplo bricks.

Step 5: Glueing

Next, you will need to erase pencil's marks and decide what side of the cardboard became a face side or a back one.

Then, you will need to cut a bottom sheet. It should have the same shape as the front sheet. I recommend placing the bottom layer in the opposite direction to the face sheet (see the picture). It makes our product much harder.

Next, you will need to glue the face sheet and the bottom layer. Press a glued sandwich by smt heavy, for example, a big water bottle or a pile of books. Let it stay under pressing for 8-12 hours.