A dado joint earns its place in almost every cabinet, shelf, and casework project because it is strong, fast to cut, and self-locating: the shelf sits in the channel and cannot slide sideways during assembly. Router-cut dados also demand planning before the router turns on, because width, depth, bit geometry, and the cutting platform all interact. The choices start with router power and performance, since the motor must drive the bit through the full pass without bogging down. This article covers dado sizing, fixed-base versus plunge routers, router table setup, bit and shank selection, and how to match the whole package to the work your shop actually does.
Sizing Dados: Width, Depth, and Fit
The dado width is fixed by the bit you install, so decide the shelf or panel thickness first. A 3/4-inch shelf calls for a 3/4-inch bit, and a 1/2-inch panel calls for a 1/2-inch bit. Depth runs one-third to one-half of the material thickness: 1/4 inch deep in 3/4-inch plywood leaves 1/2 inch of material below the channel, which is more than enough strength for typical shelf loads.
Reading the material, not the label
Nominal lumber dimensions rarely match reality, and plywood is worse: a sheet labeled 3/4 inch measures 0.718 to 0.750 inch. Measure the actual panel with calipers before choosing the bit, and cut test joints in the same stock. When you are selecting a wood router for beginners, base type and collet size matter as much as horsepower, because both affect how precisely you can set and hold the depth.
Fit classes and clearances
| Fit | Clearance per side | Typical use |
|---|---|---|
| Snug | 0 to 0.002 in | Glued case joints |
| Sliding | 0.003 to 0.005 in | Adjustable shelving |
| Loose | 0.006 to 0.010 in | Painted interiors, seasonal movement |
A snug fit that still slides with hand pressure is the target for most shelving. Test the fit with the actual panel before assembly, and remember that paint or finish adds a few thousandths of an inch to the shelf thickness.
Fixed Base vs Plunge Routers for Dado Work
Both router types cut dados well; the difference is how they start the cut. A fixed-base router is set to depth and lowered onto the work at the edge, which suits through dados that run from one edge to the other. A plunge router drops the bit vertically into the middle of the panel, which is the only clean way to start a stopped dado. The base type also affects table use: a fixed base mounts in a router table more simply, and router table motors need enough power to hold speed under load.
Motor size and speed control
For dado work in 3/4-inch stock, 1.5 to 2.25 horsepower handles the cut in multiple passes, while 3.25-horsepower motors suit production tables and large bits. Variable speed matters for large-diameter bits: a 1-inch straight bit at 20,000 RPM burns; dropping to 14,000 to 16,000 RPM keeps the edge cool.
- 1 to 1.5 HP: light trimming, small bits, occasional dados
- 1.75 to 2.25 HP: standard dado work in plywood and hardwood
- 3+ HP: router table production, large bits, deep passes
Plunge springs and depth stops
A plunge router’s springs return the bit above the base between cuts, and the depth stop rod sets how far the bit travels. Set the stop with the router off, lower the bit onto a scrap block, and lock the rod before the first pass. On a fixed-base router, the equivalent is a turret stop with several preset depths for multi-pass cuts.
Cutting Dados on a Router Table
The router table turns the router into a stationary shaper, which is the fastest way to cut dados in long case sides and repetitive parts. The bit protrudes up through the insert plate, the fence rides the workpiece edge, and the operator feeds the panel past the bit. Selecting a router motor for router table work comes down to power, collet capacity, and above-table height adjustment, because you set depth by raising or lowering the motor rather than moving the base.
Fence, featherboards, and dust
A split fence, where the outfeed half sits a hair proud of the infeed half, supports the workpiece on both sides of the cut. Featherboards press the panel against the table and the fence, and a dust port at the bit opening collects most of the chips. Set the bit height with the router off, check it against a scrap piece, and lock everything before the motor starts.
- Mount the router and set bit height to final depth
- Position the split fence and lock it
- Clamp featherboards at the bit
- Run the first pass 1/8 inch deep, then repeat to full depth
- Feed with both hands, steady pressure, no stopping over the bit
Through dados and stopped dados on the table
Through dados are straightforward on the table: the panel slides past the bit and the channel opens at both ends. Stopped dados need a stop block clamped to the fence so the panel cannot travel past the layout mark, and the rounded end left by the bit is squared with a chisel.
Router Bit Selection for Dados
The bit is the only part of the setup that touches the wood, so its geometry sets the ceiling on joint quality. A two-flute straight bit with carbide edges is the default dado tool: it cuts a flat bottom, clears chips through the flutes, and leaves clean walls in plywood and solid stock alike. Spiral bits change the cutting action: up-cut spirals evacuate chips in deep cuts, down-cut spirals leave a cleaner top edge, and compression spirals do both at a higher price. Choosing router bits for your workshop also means matching the bit to the finish work you plan: dado bits for joinery, flush-trim bits for pattern work, and roundover bits for edges.
Bit diameter and chip load
Bit diameter sets the dado width, and larger diameters need slower spindle speeds and lighter feeds. A 3/4-inch bit removes a lot of material per revolution, so the pass depth should stay at or below 1/8 inch in hardwood and 3/16 inch in softwood and plywood. Pushing a large bit deep in one pass overheats the carbide and burns the wood.
- 1/2-inch bit: shelf dados in 1/2-inch material
- 3/4-inch bit: the most common cabinet dado size
- 1-inch bit: wide dados, needs lower speed and lighter passes
Chip clearance in deep cuts
In cuts deeper than about 1/4 inch, chips must clear the flutes or they pack, overheat, and scorch the walls. Back the bit out of the cut between passes to clear chips, run a pass at full depth to clean the bottom, and check the dado with a scrap offcut before assembly.
Shank Sizes and Collet Compatibility
The shank is the part of the bit that the collet grips, and its diameter determines how much the bit flexes under load. 1/2-inch shanks versus 1/4-inch shanks is a real performance question: a 1/2-inch shank is roughly four times stiffer than a 1/4-inch shank of the same length, which means less chatter, cleaner walls, and straighter cuts in deep dados.
Matching bits to collets
Each router accepts the shank size its collet is machined for. Many routers ship with both a 1/2-inch and a 1/4-inch collet, and the collet nut must match the collet, or the bit slips or runs out of true. Check the shank for burrs before insertion, seat the bit fully, and tighten the collet with the wrench that came with the router.
When 1/4-inch shanks make sense
Small trim routers and laminate trimmers take 1/4-inch shanks only, and bits below about 1/2 inch diameter rarely come any other way. For light dados in thin material, a 1/4-inch shank bit in a trim router is adequate. For production joinery, standardize on 1/2-inch shank bits and a router with a 1/2-inch collet.
Choosing a Router Setup for Your Workshop
The right setup depends on the volume and variety of dado work. A trim router with a 1/4-inch collet handles occasional dados in thin stock and costs little. A full-size fixed-base or plunge router covers most cabinet work, and a dedicated router table with a 3-horsepower motor turns dado cutting into a production operation. Comparing trim routers, full-size routers, and router table setups before buying prevents the classic mistake of owning three routers that do the same job.
Building the setup around the joints you cut
Shops that build cabinets cut dados every week and benefit from the table; shops that cut a dado once a month are better served by a straightedge and a good fixed-base router. Start with a router that takes a 1/2-inch collet, a set of carbide straight bits in the common diameters, and a pair of aluminum clamps for the straightedge. Add the table when the volume justifies the floor space.
Dado work rewards a simple rule: measure the material, match the bit, take shallow passes, and verify the fit on scrap. Follow it, and the joints go together square, tight, and fast, season after season.