There are few joints I use as regularly as grooves and dadoes. They may lack the flair of a dovetail or the outright strength of a mortise and tenon, but, for a functional and efficient joint, it’s hard to ask for more.
Grooves and dadoes are an integral part of most case and drawer constructions. They’re easily made with either a router or table saw (or even by hand), and secured by glue or screws. Not only do they provide mechanical strength to a joint, but these joints also make it easy to register all the pieces during assembly.
Straight bits are excellent for routing grooves and dadoes. Spiral upcut bits work particularly well when routing narrow joints.
GROOVES VERSUS DADOES.
The illustration below shows the difference between grooves and dadoes (as well as rabbets). Put simply, the difference between the two is grain orientation, and the distinction is just made to indicate how the joint will need to be cut.
DADO, GROOVE OR RABBET?
Direction & Location. The difference between dadoes and grooves is all about grain orientation. A dado runs perpendicular to (across) the grain of the wood, whereas a groove runs parallel
(with). As for rabbets, these are simply dadoes or grooves made on the end or edge of a board.
Which One First? When dadoes, grooves, or rabbets intersect, it’s a good idea to cut across the grain before cutting with the grain. This gives the second cut the chance to cleanup any chipping or tearout caused by the cross-grain cut.
WHAT YOU’LL NEED.
A great feature of grooves and dadoes is that everything you need to make them is likely already in your shop. The meat of the work can be done with a table saw and a dado stack, a router table with a selection of straight and spiral bits, or even just a hand-held router with only a single, 1⁄4" straight bit.
If you’re looking to make stopped grooves or dadoes, then a marking knife and a chisel will get the job done. Beyond those, a few simple guides are all you need, depending on what tools you choose to make certain cuts.
CUTTING THE JOINTS.
There are plenty of ways to accomplish grooves and dadoes — more than we have room to show in these next pages. I’ll focus on my preferences; however, these are common techniques that we feature in a number of our projects, so you’ll find a few references to other articles for examples of different methods.
GROOVES
Grooves are a great way to form paneled frames as well as join adjacent case pieces. Grooves can be split into two kinds: those along an edge, and those along a face.
ROUTER OR TABLE SAW.
As you can see, I prefer to make my grooves at the table saw. That said, the router table with a straight or spiral bit works just as well for making these joints.
Narrow grooves made along the edges of boards work well for frame assemblies, such as on this stile and rail for a paneled door.
Cutting an edge groove on a short, wide piece at the table saw is best done with a jig like this one. A few pieces of plywood screwed together form this jig, which straddles the fence and provides support on the face and back.
EDGE GROOVES.
The first kind of groove to discuss is the one in the photos above. Grooves on a board’s edge are great for holding tongues, tenons, and panels. Cutting them at the table saw is easy with a dado blade. Depending on the workpiece’s size, a push block may suffice for the cut, however, I prefer the jig above for larger pieces.
This vertical cutting jig consists of four plywood pieces: a tall guide piece, a cleat screwed on behind to push the workpiece, and two pieces that form an “L” to straddle the fence. This makes for a safer cut compared to a push block, plus the cleat is easy to replace once chewed up.
The router table is also a good choice, though I recommend a spiral upcut bit (page 18). These bits pull the chips out of the cut, making for a cleaner groove. If you’re routing with a bigger bit (1⁄2" or larger), you may also want to rout the joint in mutiple passes. This will make for a cleaner groove.
Wider grooves running down the face of a board are often used to join large case pieces.
For creating wide grooves in a board’s face, I use a wider push block (usually for my jointer) which allows me to keep the board flat against the table.
FACE GROOVES.
The next topic: face grooves. Making these joints is simple, whether you use a dado blade at the table saw or a straight bit in a router. When cutting these, I prefer to use the same push block I use at my jointer (far left photo). It allows me to apply pressure across the face for an even cut.
The trick when cutting these at the table saw is matching the groove to the mating piece’s thickness. Hardwood is easy enough, but you may want to undersize the dado stack and make test cuts to match the true thickness of a plywood piece.
These grooves can also be made with a handheld router and an edge guide. A long, straight board clamped down to guide the router base works well as an easy edge guide.
DADOES
Making dadoes is similar to grooves, but with a few simple things to keep in mind.
End grain joints don’t hold well with glue or screws, but dadoes provide a channel to support the mating piece.
Although you won’t have cutoff pieces when using the fence as a stop to make dadoes, kickback can still occur if there’s play between the fence and miter gauge. To avoid this, I use a block clamped to the fence as a stop.
CROSSCUT CONSIDERATIONS.
Since the blade or bit exits the piece perpendicular to the grain when cutting a through dado, there is a risk of chipping, tearing, or splintering. Luckily, these are easy things to tackle.
The outside blades of dado stacks are designed to score the edges before removing the rest of the waste, theoretically avoiding unsightly cuts. However, depending on the blades’ sharpness and the type of wood being cut, this won’t always pan out.
A longer auxiliary fence (like the one you see above) can be attached to back up the wood fibers, preventing tearout.
At the router table, use a backer board to push the workpiece through. Limiting how much material you remove at once will also help to accomplish a clean cut.Handheld routers aren’t to be left out of the conversation either. I use a T-square guide to assist, which you can see in use on the Mackintosh Cupboard (page 39).
STOPPED GROOVES & DADOES
Next, it’s time to discuss something a little more complex. There are a number of ways to make a stopped groove or dado, however, the idea is the same.
STOPPED ROUTING.
There are two kinds of stopped grooves (or dadoes). First is single-stopped, in which the cut enters from one side, but stops before going through the piece.
A single-stopped joint can be made either with a handheld router or at the router table. When routing from above, I use the T-square guide I mentioned. Simply rout along the guide and stop when you reach the marked layout line
At the router table, I lay out the edge of the bit on the fence and the stopping point of the groove or dado on the workpiece. I rout until the lines meet, then turn off the router and remove the piece. You can see this in action when routing the dividers on the Mackintosh Cupboard (shown on page 41).
DOUBLE-STOPPED GROOVE.
Double-Stopped Groove. A double-stopped groove (or dado) works well to accept tenons or tongues in shelves and dividers. This joint can be made by positioning stop blocks at either end of the router table fence to control the length of the cut. Then, start the router, lower the workpiece onto the bit, and run it from the first block to the second.
The other variety of this joint is made in the center of a workpiece and is stopped on both ends. The illustration at the bottom of the previous page shows how one is made. The same concept as before is used, but instead of routing to a stopping point, stop blocks register the ends.
Stop blocks can also be used on single-stopped grooves and dadoes for easy repeatability, however they have a drawback. You’ll need to form a chamfer on the stop block’s inner corner to allow for chip clearance, but some sawdust may still build up. If it does, it can create the slight, fuzzy tiers at the end of the dadoes. Although this isn’t very appealing, it’s an easy problem to fix during the next step: squaring the groove or dado.
SQUARE UP.
The box above below the steps for squaring a stopped end. A bit of chisel work will leave you with a joint suitable for nearly any project.
SQUARING UP THE ENDS
Score. A marking knife will improve the accuracy of your chisel work, giving you a kerf to physically register the tip of your chisel in.
Perpendicular. First, chop across the grain. This will help prevent splitting or tearing as you work.
Parallel. Chop parallel to the grain to remove waste from the end and corners of the joint.
