All you need is a protractor, a cube of glass (or paperweight), 3 pins, and a piece of cardboard . Easy to follow, safe, household materials, Tested in classes over several years with success. Partial instruction as follows:
1. Staple a piece of paper to a piece of cardboard.
2. Trace a glass cube on the paper, and then put the cube off to side.
3. 1 cm from the upper left corner of the traced cube draw a normal line as shown.
4. Draw a 30º incident angle line to where the normal line meets the edge of the traced cube. Where the two lines meet is labeled point B. Where the 30º line begins is labeled point A.
5. Continue the 30º line, drawing a dotted line through the cube and beyond