Router Bits and CNC Bits: What Is the Difference?
Router bits for a handheld or table router are designed for side cutting, shaping edges and cutting grooves. CNC router bits, often called end mills, are similar, but they are designed to cut in several directions, including plunging down into the material, and they are usually used at carefully chosen feeds and speeds.
Many bits are used on both kinds of machine, but not all. Handheld bits such as large profile bits are generally not intended for CNC use. Bits are also not interchangeable with drill bits, which cut mainly along their axis; for those, see types of drill bits.
Router Bit Terms to Know
- Flutes: the cutting edges. One-flute bits clear chips well in soft materials. Two-flute bits are a common all-rounder. More flutes usually give a smoother finish and need slower feed.
- Cut direction: upcut, downcut or compression.
- Shank diameter: commonly 1/4 inch or 1/2 inch in imperial machines, and metric equivalents such as 6 mm or 8 mm. Match your collet size. See drill shank and chuck types for general shank background.
- Material: high-speed steel, solid carbide or carbide-tipped. Solid carbide is common in CNC work.
Types by Cut Action
Upcut Spiral Bits
An upcut bit pulls chips upward out of the cut. That clears chips well and often gives a clean bottom edge, but it can lift the material and cause tear-out on the top surface.
Downcut Spiral Bits
A downcut bit pushes chips downward. It leaves a cleaner top edge and helps hold thin material down, but chips can pack into the cut, so chip clearing can be an issue.
Compression Bits
Compression bits combine an upcut section near the tip and a downcut section above it. They are often used for plywood and laminated panels, where both faces need a clean edge. The bit must cut deep enough that both sections are engaged.
Types by Tip or Profile Shape
Straight (Flat) Bits
Straight bits cut grooves, dados and rabbets and flat-bottomed pockets. Spiral versions are used in CNC, and straight-flute versions are popular for plastics and some materials where a spiral could lift the work.
Ball Nose Bits
A ball nose has a rounded tip and is used for 3D carving, contouring and smooth, rounded grooves. Tapered ball nose bits suit finer detail.
V-Bits
V-bits have a pointed profile at set angles, commonly 60 or 90 degrees. They engrave, carve lettering and cut chamfers.
Surfacing (Spoilboard) Bits
These are wide, flat bits used to level the spoilboard or flatten a surface. They have a large cutting diameter and are run at a shallow depth.
Roundover, Chamfer, Cove and Core Box Bits
Profile bits shape edges. Roundover bits round an edge. Chamfer bits cut an angle. Cove bits cut concave profiles, and core box bits cut a half-round groove.
Chipbreaker and Specialty Bits
Chipbreaker or “corn” bits have serrations on the flute that break up chips, which helps in rough cutting. Diamond-cut and other specialty bits exist for particular materials. Specific claims differ by manufacturer.
Choosing a Bit by Material
| Material | Common choices |
|---|---|
| Solid wood | Upcut or downcut spiral, straight bits |
| Plywood and laminated panels | Compression or downcut |
| MDF | Downcut or compression |
| Plastics such as acrylic | Single-flute or O-flute, often upcut |
| Aluminium | Specific single-flute bits with lubricant |
| Foam | Specialised bits |
Treat the table as a starting point. Manufacturers publish their own recommendations on materials, speeds and feeds.
Tips for Better Results
- Start with the manufacturer’s feeds and speeds and adjust based on how the cut looks and sounds.
- Take shallower passes in harder materials.
- Clamp or vacuum the work securely.
- Replace bits that are dull or chipping, because they burn the edge.
- Wear eye and hearing protection and use dust control.
FAQ
What are the different types of router bits?
Common types are straight bits, spiral upcut and downcut bits, compression bits, V-bits, ball nose bits, roundover and chamfer bits, and surfacing bits.
What is the best bit for a CNC router?
There is no single best. A 1/4 inch two-flute upcut spiral is a common first bit for general work, but the right choice depends on the material and finish.
Are CNC bits the same as router bits?
Often they are similar, but CNC bits are designed for the type of cutting a machine does, including plunging. Handheld bits do not always suit CNC use.
What do CNC bits do?
Each type does a different job: cutting through, engraving, carving, surfacing, chamfering or shaping edges. For cutting larger round holes in wood on other machines, see types of hole saws.