Climb vs conventional cutting on a CNC router
Climb cutting has the tool rotation moving in the same direction as the feed. It generally leaves a better finish on wood and is the usual choice on a modern CNC. Conventional cutting is the opposite, is more forgiving on a machine with backlash, and is better in some cases like the last pass in figured grain.
The difference in one picture
The bit spins clockwise looking down on it. Now imagine it moving along an edge:
The important consequence is in that first half sentence: in conventional cutting every chip starts at zero thickness, which means every cut begins with the edge rubbing before it bites. In climb cutting, the edge bites immediately and thins out as it leaves.
What each does, in practice
| Climb | Conventional | |
|---|---|---|
| Surface finish in wood | Generally better | Slightly rougher, more fuzz |
| Heat | Lower, chips carry heat away | Higher, because of the rubbing entry |
| Tool life | Usually better | Slightly worse |
| Wall surface | Cleaner: the chip starts thick and the edge leaves the wall as the chip thins | Slightly more fuzz: the edge rubs the wall before it bites |
| Machine with backlash | Dangerous: the tool can pull into the slack | Safer: the load holds the slack closed |
| Hand routing | Grabs and runs. This is why hand routers are used conventionally. | The standard and safer way |
| Hard, brittle or figured material | Can chip out on entry | Gentler entry |
How CAM expresses it
Most CAM asks for cut direction as climb or conventional, and sometimes as clockwise or counter-clockwise. The relationship reverses depending on whether you are cutting inside or outside a shape, which is why picking clockwise or counter-clockwise by hand is a good way to get it backwards. Use the climb and conventional labels where they are offered and let the software work out the geometry.
When direction actually decides the outcome
- Plywood veneer. The direction the tool exits at the edge of the top veneer decides whether it tears. This interacts with upcut versus downcut, which usually matters more.
- Figured or interlocked grain. Where grain direction reverses within one board, no single cut direction is right everywhere. Light finishing passes matter more than direction here.
- Long grain versus end grain. The same direction produces different results on different faces of the same part. See grain direction.
- Thin walls and fragile parts. Conventional pushes away from the cut, climb pulls into it. On a delicate part that difference can decide whether it survives.
The practical answer for most people
Use climb for finishing passes on a machine with no meaningful backlash, because that is where finish quality shows. Use conventional if your machine has slack you have not fixed, or if a particular piece of figured grain is tearing out and you want a gentler entry. And if a cut is tearing out badly, remember that direction is the third thing to try: sharpness and bit type usually matter more.