Cut cleaner dadoes and rabbets

A tablesaw works great for making rabbets, grooves, and dadoes—if you have everything set up correctly. Follow these tips to avoid tear-out that can ruin your project.

WOOD words

What’s the difference between a dado, groove, and rabbet? All are partial-depth (flat-bottom) cuts, typically ¹⁄₄ " or more wide with 90° walls, known as shoulders. A dado and a groove have two shoulders, but you cut a dado across the grain, while a groove runs with the grain. A rabbet has just one shoulder because it runs along the edge or end of a workpiece, either across or along the grain.

Set the correct width

When using a dado set, you must stack up the right amount of chippers (inner blades) and shims to cut a precise-fitting channel. Multiple test cuts—and the ensuing adjustments—take time and extra material, so try this technique to get the right fit, usually on your first attempt.

Start by stacking the outer blades and chippers on the saw’s top, below, next to the workpiece that goes into the dado or groove. Add shims on top of the the stack until it feels like it matches the workpiece thickness. Install that stack onto your saw, make a test cut in scrap stock, and insert the mating workpiece into the groove. Add or remove shims, if needed, to fine-tune the fit.

Measure against your board. With the blades, chippers, and shims lying flat, rub your finger atop the stack until the shims feel flush with the workpiece.

SHOP TIP

A thin smear of petroleum jelly on a dado shim keeps it from falling into the arbor threads and getting crimped when you tighten the arbor nut.

Thwart grain tear-out

Dado stacks, because of their width and mass, can tear chunks and chips from your workpieces. So protect your project from two types of tear-out. First, prevent edge grain tear-out (like that shown above) by backing up the cut at the exit point with a scrapwood extension on your miter gauge or sled, below.

Call in backup. By supporting the workpiece with a zero-clearance insert and miter-gauge extension, you cut a tear-out-free dado (inset).

Second, face-grain tear-out—particularly problematic on veneered sheet goods—can be headed off in several ways:

•Install a zero-clearance insert on your saw. This insert supports the wood fibers at the point of cut, making for a cleaner cut.

•Use a dado set with 32–40 teeth on the outer blades. More teeth mean a smaller bite for each tooth, and less tear-out

•Finally, make a shallow (¹⁄₁₆ " or so) scoring pass first to slice through only the surface fibers, below. Then set the blade to final height and make a second pass. Don’t force the workpiece through the cut too quickly; let the blade do its work.

Score before making a full-depth cut. Score veneered plywood and tear-out-prone woods about 1⁄16" deep. This shallow cut shears the veneer cleanly instead of pulling it down.

Cut to even depths

Any time you cut dadoes, grooves, or rabbets, be sure they’re of consistent depth along their lengths. You have two options here: Hold the workpiece flat to the tabletop with a featherboard or hold-down, below, or simply apply hand pressure on both sides of the blade throughout the cut, below.

Enlist a hold-down or two. Clamp a featherboard to the rip fence in line with the blade for maximum hold-down. Add a clamp to the fence to prevent lifting.

Apply firm downward pressure. When a featherboard can’t reach, simply use both of your hands to push the workpiece against the tabletop as you push it through.

Forget the scale

With left-tilt tablesaws, you stack dado blades on the arbor from left to right—toward the rip fence. That means you can’t use the fence’s scale—calibrated for a single blade—to position the fence for dadoes. Instead, you have to measure between the blade and fence with a rule to set the
distance. (On a right-tilt saw, the fence scale will still be accurate for dado cuts.)