Router Bit Types Explained

The six families of router bit

1. Straight bits

The plainest bit there is: a flat-bottomed cutter that mills a square-walled groove. Straight bits cut dados across a board, grooves along it, and rabbets when you run them against a fence. They are also the bit most people buy first, because a dado and a groove are the backbone of shelving, drawer bottoms and cabinet backs. Sizes are quoted by cutting diameter — 1/4, 3/8 and 1/2 inch cover most casework, and a 3/4-inch bit is handy for wide dados in one pass if your router has the power for it.

2. Spiral bits (up-cut, down-cut, compression)

A spiral bit is a straight bit with a helical edge, like an end mill. The helix shears the fibers rather than chopping them, so the cut is cleaner and quieter, and the chips get moved along the flute. Direction is the whole story. An up-cut spiral lifts chips out of the slot — ideal for mortising, where packed chips are the enemy, but it tends to lift and fray the fibers at the top edge. A down-cut spiral pushes down, so the top surface stays crisp, at the cost of packing chips into the bottom of a deep slot. A compression bit combines both geometries to leave clean faces on plywood and veneered panels. Spirals cost noticeably more than straight bits, and they are worth it on visible work and on mortises.

3. Flush-trim and pattern bits

These carry a bearing the same diameter as the cutter, so the bit copies whatever the bearing rides against. Put the bearing on a template and you get an exact copy of the template; put it on the substrate under an oversized edge banding or laminate and you get a perfectly flush edge. The only difference between a "flush-trim" and a "pattern" bit is where the bearing sits — at the tip or up by the shank — which changes whether the template goes under or on top of the work. Owning one of each is what makes template routing practical, and template routing is what lets you make ten identical parts.

4. Edge-forming bits: roundover, chamfer, cove, ogee

This family is decorative and almost always bearing-guided, so the bearing rides the edge of the board and sets the cut depth for you. A roundover softens a sharp arris into a radius — the single most useful profile in a shop, because a 1/8-inch roundover makes a shelf feel finished and stops the edge from chipping. A chamfer cuts a flat bevel, usually 45 degrees, and is the tidy alternative to a roundover. A cove is the inverse of a roundover, cutting a concave scoop, and an ogee is the classic S-curve you see on table edges and molding. Buy one roundover and one chamfer first; add the rest when a project actually calls for them.

5. Rabbeting bits

A rabbeting bit cuts a step along an edge — for a cabinet back, a glass panel or a shiplapped joint. Most are sold as a set with interchangeable bearings, and swapping the bearing changes the width of the rabbet without changing the cutter. That is genuinely useful: one bit and four bearings covers most of the rabbet widths a small shop needs, and the bearing reference means you do not have to set up a fence.

6. Joinery bits: dovetail, rail-and-stile, raised panel

The last family exists to cut joints. A dovetail bit is the angled cutter that a template jig steers — the jigs in our dovetail jig roundup are all built around one. Rail-and-stile sets cut the mating profile and groove for a frame-and-panel door, and raised panel bits shape the panel that sits inside it. The last two are large-diameter, table-only bits: they need a router table, a 1/2-inch shank, a router with real power, and a slowed-down speed setting. Do not attempt them freehand.

Carbide, HSS and what "cheap set" really means

Nearly every bit worth owning today has brazed carbide cutting edges on a steel body. Carbide holds an edge far longer than high-speed steel in abrasive material like MDF and plywood, which is where most home-shop routing happens. Solid carbide is used for small spirals, where a brazed tip would be impractical.

The visible difference between a budget multi-bit set and a good individual bit is usually the thickness of the carbide, the quality of the grind and how well the bit is balanced. A thick carbide tip can be resharpened several times; a thin one is effectively disposable. This is why the honest advice for a first router is to buy a small set to learn which profiles you actually reach for, then replace the two or three you use constantly with better individual bits rather than buying a 60-piece boxed set you will use a fifth of.

How to run a bit without ruining the cut

Three habits do most of the work. Take shallow passes. A deep single pass loads the bit, burns the wood and invites kickback; two or three lighter passes cut cleaner and faster in real terms. Feed against the rotation. Handheld, that means moving left to right on the outside edge of a workpiece so the bit pulls itself into the cut rather than skating along it; in a table, feed right to left against the fence. And slow down for big bits, per the maker's stated maximum RPM.

One more that gets skipped: seat the shank properly in the collet. Push the bit all the way in, then withdraw it a couple of millimeters so the shank is not bottomed out against the collet base, and tighten firmly. A bit that creeps out of a collet mid-cut ruins the workpiece and is genuinely dangerous.

Dust, because routers make the worst kind

Routing produces very fine dust in large volume, and it is thrown at head height. A router is the tool that most often convinces a shop to take extraction seriously. Handheld routers have small ports that suit a shop vac; a router table collects far better because you can pull from both the fence and the enclosure below. Either way, wear a mask — see our respirator roundup— because routing MDF in particular puts a lot of very fine particulate into the air.

What we could not verify

We have not run controlled cutting tests comparing brands of carbide, and we do not publish tool-life numbers, because we do not run a lab. Everything above is the standard, widely documented behavior of each bit family plus the manufacturers' own published guidance on shank size and speed. Where a specific bit matters to a purchase decision, we say which one and why in the relevant roundup.