Using a jig to rout a dado or groove can give you fast, accurate results. That is, if the jig isn’t too complicated and doesn’t take a lot of setup. That’s why I like the Precision Router Dado Jig from Infinity . With this jig, you’ll be routing a dado in as little time as it takes to apply a clamp to a board.
ACCURACY. The jig consists of a cast aluminum base that fits over and slides along a straightedge clamp, as shown in the top photo. Included with the jig is a guide bushing that fits into an opening in the adjustable carriage, as you can see in the left photo. The bushing attaches to your router’s baseplate and locks the router to the jig for clean, accurate dadoes.
BUSHING. With this bushing you can use a bit up to 3 ⁄ 4 " in diameter. This means you won’t have to make as many passes for wide dadoes. And the bushing allows you to lift the router off and on the jig easily, so you can make adjustments quickly. This feature is one of my favorites. It really saves time when I’m making wide or multiple dadoes in a workpiece. I can also adjust the depth of my router bit without having to work around the jig.
LENGTH. Another feature I like about this jig is that it rides on a straightedge clamp. (The clamp is not included.) This means that the length of your dado is limited only by the length of your clamp. So you can rout dadoes in wide workpieces, like case sides. And the jig adjusts to fit different sized straightedge clamps.
DIAL IN. Dialing in a precise dado width is easy with this jig. If you take a look at the second photo from the top, you’ll see the adjustable carriage in the jig that holds the bushing. This carriage slides side-to-side by means of a micro-adjustable screw. An indicator scale printed on the jig lets you know how far you’ve moved the carriage. Once positioned, the carriage can be locked in place by means of a locking nut.
GUIDE SYSTEM. On the underside of the jig you’ll find a bar that guides the jig along the straightedge clamp (drawing, third from the top). An adjustment screw on the end of the jig draws the guide bar to the straightedge evenly, and a locking nut holds it in place. Set screws on the top of the jig can be tightened down to keep the bar from racking. Across from the guide bar are two steel rollers that help the jig glide on the straightedge. When adjusting the guide bar to the straightedge clamp, you want the jig to slide freely without slop.
SET-UP. Located on the front of the jig are three small index marks (two photos above.) Each mark indicates the inside edge of a particular size of bit. To position the straightedge clamp and the jig in one step, all you need to do is lay the straightedge clamp on the workpiece with the carriage zeroed out. Then align one of the index marks with the layout line of your dado, clamp the straightedge to your workpiece, and you’re ready to rout dadoes.
After you’ve made the first pass with the router, you can widen the dado by moving the micro-adjust screw (photo above). Just loosen the locking nut and turn the screw for a precise fit of any width. The indicator scale is marked in 1 ⁄ 16 " graduations. And it’s easy to check the width of your dado after each pass (right photo).
RABBETS. The jig routs rabbets as easily as it does dadoes. But I set the adjustable carriage at the center of the indicator scale to balance the weight of the jig. I cut the edge of the rabbet first and then worked my way in for a wider rabbet.
I found this jig to be one of the best I’ve used. It’s simple setup and ease of use out-classed other dado jigs I’ve tried. I think you’ll find it delivers perfect dadoes every time. And it can be done without spending a lot of time setting it up.
Cleaner Dadoes: Spiral Downcut Bit
Using a spiral downcut bit to make dadoes, grooves, or rabbets in plywood guarantees a nice clean edge. It even limits tearout in hardwood, too.
The spiral bit is designed to sheer down so that the top veneer of the plywood doesn’t tear out. I keep a 1 ⁄ 2 "-dia. bit on hand to cut wide dadoes in two passes. Spiral bits are available from 1 ⁄ 8 " to 1 ⁄ 2 " in diameter. There’s more information in Sources on page 51.