How to Make a Cardboard Template for a Corner Shelf
If you build a shelf this way, there will be gaps on either side of the shelf that will not lean flat against each side of the wall.It is better to cut a simple template from the cardboard to get the depth and angle of the shelf and then transfer it to the wood.Put a large piece of cardboard in the corner.
The corner of the cardboard should be docked with the corner of the wall.Measure both sides of the cardboard from the corner.Make a mark on each side indicating the depth of the shelf-where the surface of the shelf will terminate.
Put the ruler on the cardboard where you make the mark.Draw a line on the cardboard with a ruler, from one mark to another mark.Place the cardboard on the workbench.Cut a triangle along this line with a tool knife.
This is the footprint of the corner shelf.Insert the triangle into the corner.Check the fit on both sides.If there is a gap between the wall and the cardboard, you need to expand the angle.Trim the sides of the cardboard with scissors, and when you cut it from a corner outside to the corner of the wall, tilt the line slightly.
Check if it is appropriate and trim the cardboard as needed until the two sides of the template fit