noun: dado; plural noun: dados
the lower part of the wall of a room, below about waist height, if it is a different color or has a different covering than the upper part.
a groove cut in the face of a board, into which the edge of another board is fixed.
the part of a pedestal between the base and the cornice.
The above definition was lifted directly from a Google definition search. As a woodworker, I had never heard of two thirds of the definitions above. How about you?
A little more research reveals that, in North American terminology, a dado is technically a groove that runs perpendicular to the grain of the wood. A groove running parallel to the grain is, well, a groove.
A dado (or a groove) can run completely through the width or length of the board, or it can be “stopped”. That means it doesn’t go through, but is closed. But only at one end, because if is closed on both ends, it becomes a “mortise”.
Gotta love the English language!
Dados seem to be most often used to make a cross-grain, 90 degree joint between two boards. A good example is the attachment of shelves to the sides of a book case. Compared to a simple butt joint, even with nails or screws to fasten it, the dado joint is vastly stronger. It provides some gluing surface around the end of the housed board, but it also provides mechanical support against the direction of force that is normally applied to the shelf.
As with most woodworking operations, there are a number of ways to make a dado or groove. Hand tool users may choose to define the walls of a dado with a saw, then plow out the waste with a chisel. A router plane might be used to refine the bottom to a smooth, consistent depth.
Users of hand-held power tools often turn to the router, usually with a guide of some sort.
For quickly creating dados in any quantity, its hard to beat the table saw. While it is perfectly acceptable use a standard blade to nibble away the stock, there is a better way. Many years ago, some wise person discovered that stacking saw blades together worked pretty well. Over time, the blade stack was refined to include two outer cutting blades, inner chipping blades, and shims or spacers to fine-tune the width of the stack. Some styles use a center blade set on an angle, to remove the waste. All these devices are commonly referred to as “Dado Stacks”.
While it would seem that a dado stack is fairly straightforward in how it works, there are actually several nuances to consider:
- The style that uses an angled center blade is often called a “wobbler”. These units are usually less expensive, and often quicker to adjust for cut width. However, the nature of the design means they will never produce a truly flat bottom to the cut.
- Some styles of stacked-blade sets make a compromise between clean sidewall cuts and perfectly flat bottoms. They use a tooth grind known as ATB or Alternate Top Bevel, which aids in slicing the surface fibers cleanly along the edges, but also leaves a pointed track inside each bottom corner, sometimes known as “bat ears”. This is not important, unless the end of the dado will be visible in the finished piece.
- Stacked Dado sets with FTG or Flat Top Grind teeth will produce the cleanest bottom of the dado, but require different rake angles and slower feed rates to minimize tearing of the fibers along the edges of the cut.
- There are also specialized “grooving blades” available, which are thicker than a standard saw blade, and have teeth sized to cut the desired dado or groove exactly. These are not common for hobbyists, but often seen in professional shops where frequent repetition of the same width dado or groove is more likely to be necessary.
To use a dado stack, first remove the regular saw blade, and the splitter or riving knife, if your saw has one. Note that some saws have very short arbors, and may not accommodate the full width of your dado stack. This is most often true of machines originally designed for the European market, as some European countries have safety regulations against the use of dado stacks. It is also true of many benchtop or ‘contractor’ type saws, although most can take 3/8″ to 1/2″ stacks. Full cabinet saws intended for the U.S. market should be able to accept the full 7/8″ offered by many dado sets.
You may wonder why dado sets are not typically found in the same diameter as the blade your saw normally uses. There are two reasons for this.
First, the intended use of a dado set is for cutting wide, but relatively shallow, kerfs. The need to cut more than 1″ deep is practically non-existent.
Second, the extra mass of the dado set puts more strain on the saw’s drive line. Reducing the diameter to 8″ or 6″ reduces the mass, and the strain on the motor. Unfortunately, it also reduces the linear cutting speed, so feed rate must be reduced accordingly.
Once the arbor nut, flange washer, and regular blade are removed, slide the outer cutting blade of the dado stack on. Make sure the teeth are facing the proper direction. Follow this with alternating shims and chippers, and at last the other cutting blade. When properly assembled, the cutting teeth will provide an overlapping cut to avoid ridges. Remember to rotate the chippers such that their combined mass is evenly distributed around the circle, and that none of the cutting teeth contact one another. Reinstall the flange washer and arbor nut. Once the nut is tight, the stack is ready to go.
Be aware that the dado stack will very likely require a different throat plate insert. Most factory inserts have a gap of around 1/2″, and you should be using a zero-clearance throat plate insert for normal blades, anyway. Now is a good time to make or buy a new insert to fit your saw. As an alternative, you can do most dado operations with the work piece on a saw sled. Cutting grooves or rabbets with the dado set will require an insert, or some other way to close the large gap around the blade, otherwise the work piece will drop into the opening and ruin the cut, or cause an injury.
When making the actual cut, feed the work a bit slower that you would with a regular blade. Remember, this stack of blades has to remove a pretty large amount of material. Feeding to quickly will result in more tearing of the cut, and wear on your saw.
Dado stacks can be used for many different woodworking joints.
- Aside from a simple through dado, stopped dados can be cut by passing the work part way across the cutter, then squaring up the corner with a chisel.
- Grooves are cut like a dado, but referencing the long side of the work piece against the saw’s fence.
- Rabbets are cut using the same techniques as dados or grooves, except that the cutter is usually buried into a sacrificial face when the cut is referenced against the saw fence.
- Using the rabbeting technique around all four sides of a board, at it’s end, produces a tenon for mortise and tenon joints.
- A simple jig works with a dado set to create box or finger joints.
- A wooden fence clamped at an angle across the saw table allows the set to cut various profiles for molding.
I’m sure there are many more that will come to mind as soon as I hit “Publish” on this post!
To see more details, and a short review of the dado stack I recently acquired, take a moment to watch the video below.
Now, go make something!