Materials Needed:

1/2" Acrylic sheet, cut @ 4"x 8"
2x4 Lumber (real dimensions 1.5"x 3.5"), about 12" length
Black cardboard or thick paperboard (~1/8" thick), cut @ 7"x 10"
One 2" wood screw

Approximate Building Materials Cost:

Acrylic $2.50
2x4 $.50
Cardboard/Paperboard ~$.10
Total $3.10

Tools Needed:

Table saw
Band saw (optional but recommended for cutting acrylic)
Coping Saw (for wood, if band saw is not available)
Radial saw
Large disk sander (optional but recommended)
Coarse wood file
Coarse (100), medium (300), and fine (600) grit wet/dry sandpaper
Buffing wheel with buffing compound (optional)
Soft polishing rag
Plastic polishing compound (toothpaste also works)
Drill with various bits
Screwdriver
Combination square (for marking 45 and 90 degree cuts)

Assembly Instructions:

1. Using the radial saw, cut the 2x4 to get an approximately 7" long piece and set it aside.
2. Set the radial saw to cut at 45 degrees, and cut the remaining piece at 45 degrees with the cut ending at the corner. Reset the saw to a square cross-cut and cut off the angled part so that you end up with a small right triangle with sides of 3.5" each.
3. Set the table saw blade height to 1/2". Cut a blade-width (1/8") groove into the 7" wood piece. This groove is on the face of the 2x4, parallel to the long side, and 1/2" in from the long side. This groove will hold the cardboard back-piece.
4. Keeping the table saw blade at 1/2" height, cut a 15/32" wide groove into the hypotenuse of the small triangular wood piece. This slot will hold the plastic prism. Since the plastic will often not be exactly 1/2" (usually a little less), you can use a wood file to slightly widen the groove so that the prism will fit snugly. Don't widen the slot until after you finish the prism.
5. Using either a band saw or coping saw, cut off a curved portion from the hypotenuse of the triangular wood piece as shown. This will keep from hiding the side of the prism that fits into the wood so it is obvious that there are no hidden tricks.
6. Sand the wooden pieces as you see fit.
7. Mark the acrylic piece at a 45 degree angle from one corner to the middle of one of the long sides. One side should be 4" and the opposite side should be 8". Using masking tape to mark the cut is recommended, as marker or pencil can easily smudge or be wiped off the plastic. Using either a band saw or radial saw, cut the acrylic piece along the mark.
8. If available - use a large disk sander to sand the edges of the prism flat, removing the saw marks. Otherwise sand the edges with wet coarse sandpaper. Sanding the sides flat and square is best done by putting the sandpaper down on a hard, flat surface (countertop, lab bench, etc.) and rubbing the prism against it.
9. Sand the edges of the prism with wet medium grit sandpaper. Repeat with wet fine grit sandpaper. There should be no scratches visible with the naked eye.
10. If a buffing wheel is available, use it to polish the edges of the prism. Otherwise use a rag with polishing compound. The edges need to be as clear as possible or some of the laser light will be scattered and the desired reflection effect will be diminished. A good test to check the finish on the edges is to hold the prism over some text and look through the edges at the text. Slowly pull the prism farther away from the text. The farther you can take the prism away from the text without the text blurring the better the finish.
11. Check if the prism will fit into the slot in the triangular wood piece. If it is too tight, then use a wood file to slightly widen the slot until the prism fits snugly. If the prism is too loose, then a little glue can be used at the corners to hold it in place when you assemble it later.
12. Place the triangular wood piece on the top face of the wood block with the slot facing up as pictured. Hold the triangle piece in place firmly, and using a drill bit that is the same diameter as the screw (including threads), drill through the triangle at a slight angle (this crosses the grain to avoid splitting the wood) until the drill bit just barely passes into the base block.
13. Keeping the triangle in place, switch to a thinner drill bit for the base block. The screw will then bite into the base block without putting pressure on the triangle piece. Drill into the base block through the hole drilled into the triangle. If you have a countersink bit, countersink the hole in the triangle piece for the screw head.
14. Attach the triangle piece to the base with a wood screw.
15. Fit the cardboard/paperboard into the slot in the base as shown.
16. Fit the prism into the slot in the triangle piece as shown. If the fit is a bit loose, use a small bit of glue at the corners to hold it in place. Avoid getting glue on the edges of the prism, as this will affect its reflective properties.

*Note: The finish on all the edges of the prism are critical. For a better finish, use superfine (1000 grit) wet sandpaper before buffing/polishing. Also, this project calls for 1/2" plastic (that's what we had on hand). It would be better to use thicker (3/4" or 1") plastic.