A dado is a flat-bottomed channel cut across the grain of a board, and it is the workhorse joint of cabinet and shelving construction. Shelves drop into dados cut in the case sides, drawer dividers lock into place, and bookcases gain stiffness that butt joints cannot match. A router with a straight bit cuts these joints quickly and repeatably, and the quality of the result depends more on setup than on the router itself. Router power and performance still matter: a plunge router with a 2-horsepower motor and a 1/2-inch collet handles 3/4-inch plywood dados in fewer passes than an underpowered trim router. The sections below cover joint types, three cutting setups, bit selection, a step-by-step pass sequence, and the fixes for the most common mistakes.
Dado Basics: Types, Depth, and Fit
Before cutting, decide which joint you actually need. A dado runs across the grain, a groove runs with the grain, and a rabbet removes a step from an edge. Through dados run from one edge of the board to the other; stopped dados end short of the front edge so the joint is invisible from the outside of the piece. Shelf standards in cabinet construction call for dados cut one-third to one-half of the way through the workpiece material, which leaves plenty of strength in the remaining material.
Precision routing depends on controlling the bit’s path, and the same precision router techniques used for scribing shingles at outside corners apply here: lock the router to a reference edge, keep the base flat, and let the bit do the cutting. A dado that is 1/32 inch too tight will split the shelf when it is driven home, and one that is 1/32 inch too loose rattles and needs shims.
Fit classes for dado joints
| Fit | Clearance | Use |
|---|---|---|
| Snug | 0 to 0.005 in | Permanent glue joints |
| Sliding | 0.005 to 0.010 in | Adjustable shelves |
| Loose | 0.010 to 0.015 in | Painted or hidden joints |
Measuring the fit
The dado width equals the bit diameter, so a 3/4-inch shelf needs a 3/4-inch bit, and the depth is set with the router’s depth stop or by measuring from the base plate to the bit tip with a ruler. Test cuts on scrap from the same board stock are the only reliable way to check fit, because nominal 3/4-inch plywood measures 0.718 to 0.750 inch depending on the manufacturer.
Three Setups for Cutting Dados
Three setups cover nearly every dado job: a straightedge clamped across the work, an edge guide riding the workpiece edge, and a router table with a fence. Each trades setup time against repeatability.
Straightedge and clamped guide
For one-off dados, clamp a straight board across the workpiece at the layout line and run the router base against it, adding the offset between the bit edge and the base edge. This setup is cheap and accurate, and it is the method most beginners should start with.
Edge guide
An edge guide runs parallel to the workpiece edge and suits dados near that edge. Many router accessory bundles include an edge guide, extra collets, and a set of bits, which covers the basics without separate purchases. The guide’s reference surface must sit on the same edge for every pass, or the dado drifts.
Router table with fence
For production runs, a router table with a split fence is the fastest setup: the fence rides the workpiece edge, the bit protrudes through the table, and the depth is fixed by bit height. The workpiece slides past the bit, so long case sides stay supported and the operator keeps both hands on the work.
| Setup | Best for | Setup time | Repeatability |
|---|---|---|---|
| Straightedge | One-off dados | 2–3 min | Good |
| Edge guide | Dados near an edge | 1–2 min | Good |
| Router table | Production runs | 5–10 min | Excellent |
Router and Bit Selection for Dado Work
The router and the bit carry the load. A fixed-base router holds a depth setting rock-steady and suits through dados; a plunge router lets you start a stopped dado in the middle of a panel. Comparing fixed-base and plunge router features before buying avoids owning two routers when one would do.
Power and collet size
For 3/4-inch plywood and solid stock, a 1.5 to 2.25 horsepower router with a 1/2-inch collet cuts cleanly. A 1/4-inch collet limits you to smaller bits and flexes more in deep cuts. The bit does the cutting: a two-flute straight bit is the standard choice for dados, and a spiral bit clears chips faster in deep cuts.
Straight bits versus spiral bits
- Two-flute straight bit: clean flat bottom, standard for dados
- Up-cut spiral: pulls chips up, aggressive, slight tear-out on top
- Down-cut spiral: presses fibers down, clean top edge, packs chips
- Compression spiral: clean both edges, best for plywood
Carbide edges last longer
High-speed steel bits dull quickly in plywood, whose glue lines are abrasive. Carbide-tipped straight bits hold an edge several times longer, and the cost difference pays off after a few projects. Check the bit for dullness by listening: a bit that chatters or burns instead of slicing is telling you to sharpen or replace it.
Step-by-Step: Cutting a Dado
The pass sequence decides the outcome more than any other variable. Set the bit depth to the final dado depth, then remove the material in several shallow passes rather than one deep cut. A 3/8-inch-deep dado in plywood cuts cleanly in three passes of roughly 1/8 inch each, which keeps the bit cool and the cut walls smooth. Bit materials and coatings drive cutting performance just as they do for oscillating multi-tool blades, so keep the edge sharp and match the speed to the material.
The pass sequence
- Mark both ends of the dado and clamp the guide
- Set the depth and make the first shallow pass
- Repeat at 1/8-inch depth increments to full depth
- Run a final full-depth pass to clean the bottom
- Square stopped-dado ends with a chisel
Test cuts and feed direction
Cut a test dado in scrap from the same sheet before touching the workpiece. Feed the router against the bit rotation, left to right on most handheld setups, and move slowly enough that the motor does not labor. If the bit grabs or the router wanders, the feed direction or the guide setup is wrong. Most routers run at 18,000 to 24,000 RPM, and a variable-speed model set near 16,000 RPM with a 3/4-inch bit cuts cooler in hardwood.
Troubleshooting Common Dado Problems
Burning, tear-out, and loose or tight fits account for nearly every dado complaint. Burning means the bit is dull, the feed is too slow, or the speed is too high for the bit diameter. Tear-out at the top edge means the bit is exiting unsupported wood, which a down-cut spiral or a sacrificial backing board fixes. Speed, wear, and material selection govern cutting performance in every edge tool, and router bits follow the same rules: match the RPM to the bit size, replace worn edges, and pick the geometry for the material.
Fit problems
- Too tight: sand the dado walls or switch to a bit 1/64 inch smaller
- Too loose: shim the shelf or recut with the next-larger bit
- Wavy bottom: caused by flex, so take lighter passes or use a 1/2-inch shank bit
Burning and chatter fixes
When the wood darkens along the cut, slow the feed or sharpen the bit. When the cut walls show chatter marks, the bit is flexing: move to a 1/2-inch shank, reduce the pass depth, or both. A dado that burns on one side only usually means the guide is not square to the bit path, so check the layout line with a square before recutting. Clean the dado with a sharp chisel to square the corners of stopped cuts and remove any fuzz left by the bit.
Safety and Shop Workflow
A router at 20,000 RPM removes fingers faster than it removes wood, so the safety routine is non-negotiable: eye protection, hearing protection, and a dust collection hookup on the router or table. Keep hands behind the bit path, use push sticks on a router table, and never reach over a spinning bit to adjust the fence. Dust collection matters for visibility as much as health: chips hide the cut line, and a shop vacuum attached to the router base or table fence keeps the line visible.
Workflow that keeps dados consistent
Cut dados before assembly, when the pieces are flat and easy to handle, and group the same-size cuts so the router is set up once. Label each piece and its dado location with a pencil mark before the parts come off the bench. Carbide cutting tools such as router bits and saw blades stay accurate longer when they are stored in a dry case, wiped clean, and sharpened on a schedule, and consistent joints start with consistent tool care.
Dados reward preparation: the right bit, a solid guide, shallow passes, and a test cut. Routers make the joint fast, and the setup habits described here make it accurate enough to trust for years of shelving and cabinet service.