How to Make a Wood Marble Run

Cut two lines with the saw, ½ inch deep, and ½ inch apart, along the center of the length of the 40-by-10 plywood. Chisel out the strip along the center, so you have a channel ½ inch deep and wide along the length of the sheet.

Apply a generous line of wood glue along the bottom and sides of the channel, then slide the 40-by-40 plywood square into the channel so that it is perpendicular to the 40-by-10 base. Let dry.

Drill in the angle brackets on either end of one side of the plywood square and base to secure the upright square.

Glue the plywood strips to the sides of the planks so that each plank has a barrier on one side. Let dry.

Glue one plank starting from the top of the square at a downward angle of about 20 degrees. Use the side of the square without the angle brackets. There will be around 1 inch space between the end of the plank and the other side of the plywood square. Make sure the barrier edge is facing outward.

Glue a second plywood plank starting from the opposite side of the square, directly underneath the space left by the end of the first plank. This plank should be at the same 20-degree downward angle. Repeat this zigzag pattern with the remaining three planks, ensuring that the barrier side is outward on all of them. Let dry.

Drop a marble onto the top of the first plank, and watch as it rolls along its length, falls through the gap between the side and the plank, onto the second plank, and keeps rolling down in this way.