A simple jig and a pattern cutting bit make big dados a small concern.
My friend, Tim, showed up recently with the need to make a sign frame out of 4 x 4s. In order to make the frame for the sign rock solid we wanted to cut dados into the vertical posts to received the horizontal parts. How to handle these 1″ deep, 3-1/2″ wide dados.The prospect of crosscutting them on the table saw seemed daunting. An 8′ long 4 x 4 just weighs too much. This project called for taking the tool to the work, not the work to the tool.Back in my carpentry days we’d commonly notch construction grade material by making MANY passes with a circular saw, then chiseling the dado flat. That works OK, but not great. I decided the answer for this project would be a hand-held router, pattern cutting bit, and shop-made jig.
Making a sign frame – Sizing the jig to the posts / Sizing the jig to the frame:
The Jig. I ran four 2 x 4s through the planer and jointer to make sure the faces and edges were flat and straight.We clamped the 2 x 4s to the vertical post and screwed them together, making sure the assembly was perfectly square.
The router and pattern bit. Next we clamped an off cut from the horizontal pieces between two of the 2 x 4s and screwed the final piece to the jig. Note the .020″ dado shims. This should provide just a little clearance between the routed dado and the horizontal component.The result is a jig that will perfectly straddle the posts and, using a pattern cutting bit, make a perfectly dimensioned dado.
Making the Cut.
Cutting dados with a hand held router. With the post clamped to a bench the jig is clamped on the lay out lines for the horizontals and the waste routed away. The large diameter of the bit makes short work of the 3-1/2″ that has to be removed.
Photos By Author