Bit Guide

Choosing the right CNC router bit

Choosing the right CNC router bit comes down to two questions: what material are you cutting, and which face has to look perfect? Answer those and the tool family — upcut spiral, downcut spiral, compression bit, O-flute — picks itself. Then match the diameter and cutting length to your part. This guide covers every type of solid carbide CNC router bit we make, when to use each one, and the mistakes that burn edges and break tools. Five minutes here saves you tearout, melted plastic, and wasted carbide.

CNC Router Bit Selection Chart: Match Your Material to the Bit

If you're cutting...	Best router bit	Why
Plywood or solid wood, general work	Upcut (Upshear) Spiral	Fast, cool cutting, clean bottom edge, best chip clearing
Veneer, melamine, or laminate where the top face shows	Downcut (Downshear) Spiral	Presses the show face down — zero top tearout
Veneered plywood where both faces show	Compression Bit	Clean top AND bottom edges in a single pass
Dados, grooves, and shallow slots in panel goods	Mortise Compression Bit	Short upcut zone (.150”–.200”) works at shallow depths
Heavy material removal in thick stock	Rougher (Chipbreaker) Bit	2–3× the removal rate; follow with a light finish pass
Thin stock, small parts, light workholding	Straight Flute Bit	Zero helix = no lifting force on the material
Acrylic, HDPE, UHMW, and soft plastics	O-Flute Bit	Polished open flutes make chips, not melted edges
Signs, lettering, and chamfers	V-Carve Bit	Angle matches your CAM v-carve toolpath
Color core laminate and fine detail	Engraving Bit	Crisp, consistent stroke width in shallow passes
3D carving and contouring	Ballnose Bit	Full-radius tip, your stepover sets the finish

Upcut vs. Downcut vs. Compression: The Three Spirals Explained

Upcut Spiral Router Bits (Upshear) — the CNC workhorse

An upcut spiral router bit has flutes that spiral upward, pulling chips up and out of the cut. That means fast, cool cutting and an excellent bottom edge — the tradeoff is the top surface can show minor fuzzing in veneered material. It's the go-to CNC bit for through-cuts, pocketing, and general routing in solid wood, plywood, and MDF.

Downcut Spiral Router Bits (Downshear) — for tearout-free top faces

A downcut spiral router bit presses the material into the table as it cuts, leaving a crisp, chip-free top edge on veneers, laminates, and melamine — the answer to veneer tearout on a CNC router. Because chips get pushed down into the cut, run slightly shallower passes than an upcut, and cut onto a spoilboard for through-cuts.

Compression Router Bits — clean edges on both faces, one pass

The compression router bit is the panel-processing essential: an upcut tip and downcut upper flutes press both faces inward, producing clean edges top and bottom in a single pass through veneered plywood and melamine. One rule matters more than any other: your first pass must be deeper than the upcut zone (about 7/16" on our standard compression bits), or the upcut tip will chip the top face. Where cutting length allows, a single full-depth pass is best practice — it's why compression bits dominate nested-based cabinet manufacturing.

Mortise Compression Bits — compression quality at dado depth

A mortise compression bit shortens the upcut zone to .150" or .200", delivering compression-quality edges in shallow cuts — dados, grooves, drawer slots, and blind pockets — where a standard compression's long upcut zone would never be buried. If you cut cabinets on a CNC, this is the bit your dado toolpaths want.

Rougher / Chipbreaker Router Bits — heavy stock removal

Serrated chipbreaker flutes shear material into small chips instead of long ribbons, dramatically cutting spindle load. Run a roughing bit 2–3× harder than a finishing spiral, then come back with a light finish pass (.010”–.020”) to erase the serration marks. We grind roughers in upshear and downshear, 2- and 3-flute — one of the deepest chipbreaker ranges made in the USA.

Straight Flute Router Bits — zero lift, total control

No helix means no axial force — a straight flute bit neither lifts the workpiece nor packs chips downward, making it the choice for thin stock, small parts held with tape or light vacuum, and precise slotting. Feed about 20% slower than a comparable spiral.

O-Flute Router Bits — the best bits for cutting plastic

A single polished, open flute with a big gullet, designed to make plastic chips and evacuate them before heat builds. In acrylic, HDPE, UHMW, polycarbonate, and PVC sheet, an O-flute is the difference between a polished edge and a melted, re-welded mess. We make straight flute O-flutes (for thin sheet that mustn't lift) and upcut spiral O-flutes (for thicker plastic where chip evacuation wins).

V-Carve & Engraving Bits — signs, lettering, and detail

V-carve bits are all about the included angle — 30°, 45°, 60°, 90°, 120° — which your CAM software uses to calculate the v-carve toolpath. Match the bit's angle to the toolpath's angle and depth takes care of itself. Our color core engraving bits are ground for consistent stroke width in sign laminates: shallow passes (.010”–.030”) and modest feed for crisp detail.

Ballnose Bits — 3D carving and contouring

A full-radius tip for 3D CNC carving, fluting, and sculptural work. Surface finish is governed by your stepover, not the bit: 8–12% of diameter for a fine finish, run at standard spiral feeds and speeds.

Router Bit Size Guide:
Diameter and Cutting Length (LOC)

Cutting length

pick the shortest LOC that clears your material thickness. Every extra bit of length reduces rigidity — a shorter, stiffer carbide bit cuts cleaner, runs quieter, and lasts longer. We stock more LOC steps than any brand in our class so you're never forced into a longer, whippier bit than the job needs.

Diameter

bigger diameter means a stiffer tool, faster feed rates, and better finish — but your inside corner radius equals the bit's radius. Cut the largest diameter your part geometry allows: usually 3/8" or 1/2" for nested cabinet parts, 1/4" and down for detail work.

What Is a FEM Router Bit?

FEM stands for Full End Mill point grind. A FEM bit plunges straight down like an end mill and leaves a flat, finished bottom surface — where a standard plunge-end spiral leaves a slightly rougher floor. If your toolpaths include plunging, pocketing, or anything where the bottom of the cut shows, FEM is worth it. Look for "FEM" in the part number.

What Does -HP Mean on Carbide Router Bits?

Our High Performance grade: a premium sub-micron carbide that holds its edge significantly longer in abrasive materials. MDF, particleboard, and glue-heavy plywood are carbide killers — HP is built for them. Running production volume in abrasive board, the HP upcharge pays for itself in fewer tool changes.

Still Not Sure Which CNC Bit You Need?

Tell us your machine, your material, and what you're making — we'll point you at the exact part number with starting feeds and speeds. Email sales@centuriontools.com or call 540-967-5402. Every bit we sell is solid carbide, ground in the USA in Louisa, Virginia. And grab our CNC Feeds & Speeds Chart — every recommendation on this page has matching numbers there.

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