Dadoes are an ideal way to attach shelves in cabinets or bookcases. They provide strength and stability to the project and help reduce warping when using solid wood for shelving. The most common method for cutting dadoes is to use a table saw with a stacked dado set. If the size and shape of your project prevent you from using this method, or you don't want to change your saw blade, a router with a straight bit can do the job just as well.
Instructions
Locate position for dado on your project. Mark top and bottom of dado with pencil. The distance between these two marks should match the thickness of the material you will use as a shelf.
Place square on top mark and draw pencil line across width of board.
Place square on bottom mark and draw pencil line across width of board. When done, the marks should be parallel.
Install bit in router. Measure distance between side of bit and edge of router base. This will give you the offset measurement for the guide fence.
Measuring from the top dado line, mark the top offset line on your project. Repeat this step for the bottom dado line. You will now have four lines on the board. The center two lines should be the thickness of your material (usually 3/4 inches) apart. The distance between the two outer lines should be exactly the width of your router's base.
You will use 1x4 lumber for guide fences. Align first fence with top offset mark. Position the board with the 4-inch face flat against the project. Align the second fence in the same manner on the bottom offset mark.
Secure both guide fences to the project with bar clamps.
Raise router bit until you can sit router squarely on project without bit touching surface. Set router between guide fences. Router should slide smoothly between fences without binding.
Adjust fences if necessary. As you slide the router back and forth, make sure the bit is kept in alignment with the lines marked for the dado.
Lower router bit to desired depth. Turn router on and make cut.
Tips & Warnings
If you plan to cut more than one or two dadoes, consider building a dado jig for your router.
If you've never used a router before or don't have enough practice with one to feel comfortable, practice the steps above on a piece of scrap a few times.
When using plywood for shelves, be aware that most 3/4 inch plywood is thinner than 3/4 inch. This means the bit that should make a perfectly sized slot will actually be a bit large. In this case, you can use a 1/2 inch bit and make one pass against the top fence and another against the bottom fence.
Always wear safety glasses and hearing protection when operating router.
Be sure router is unplugged before installing or changing bits.
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