CNC Wood Solutions: How Wood Actually Cuts

• 1
  Why wood behaves differently at the cutter
• 2
  Tool geometry and the cut: what the numbers mean
• 3
  3-axis and 5-axis routing: when each one pays off
• 4
  Species, engineered panels, and moisture paths
• 5
  What tolerance wood can actually hold
• 6
  Matching the process to the part

Wood is an anisotropic material. Its stiffness and cutting resistance change with direction. A carbide cutter pushing parallel to the grain shears fibers cleanly; the same cutter pushing across the grain lifts fibers and leaves fuzz. This is the single fact that separates CNC wood solutions from metal machining. You cannot pick one speed and feed and expect the same surface on a curved panel.

The second factor is moisture. Kiln-dried hardwood moves between 6% and 10% moisture content depending on shop climate. When the relative humidity shifts, a 600 mm oak panel can grow or shrink 2–3 mm across the width. Cut it at one moisture level and assemble at another, and your bolt holes no longer line up. Stability comes from controlling the shop, not from the machine.

Third is springback. Wood compresses under the cutter and relaxes after the tool passes. In deep pockets and tenons, the finished wall can sit 0.05–0.15 mm off the programmed line. On metal we compensate with tool wear tables. On wood we compensate with a spring pass and a slightly undersized roughing allowance.

None of this makes wood unmachinable. It means the process window is narrower and the operator has to read the material, not just the G-code.

• 1
  Grain directionSets surface finish and edge quality more than spindle speed.
• 2
  Moisture content6–10% for stable hardwood; check before every long run.
• 3
  SpringbackAdd 0.05–0.15 mm on deep pockets and finish with a light pass.

For CNC wood solutions, cutter geometry matters more than machine horsepower. A two-flute upcut spiral clears chips fast but can tear the top face. A compression spiral puts downcut flutes at the tip and upcut flutes above, so the top and bottom edges both stay clean. That is the standard choice for veneered plywood and double-sided melamine.

Spindle speed on wood runs far higher than on aluminum. A 6 mm carbide spiral in hardwood typically turns 16,000–20,000 rpm with a chipload of 0.1–0.2 mm per tooth. Push the feed too slow and the cutter rubs, which burns the edge and dulls carbide in minutes. Push it too fast and you get chatter marks and broken 3 mm tools.

Depth of cut is where most shops lose money. A 6 mm tool cutting 3 mm deep in oak is reasonable. The same tool cutting 9 mm deep in one pass will deflect, and the wall will taper. Rough in 2–3 mm steps, then take a 0.2–0.5 mm finishing pass at full spindle speed. The finishing pass is what gives you a glue-ready edge.

Tool wear shows up as a change in sound before it shows up in the part. When the pitch of the cut rises, the edge is dull. Change the tool, not the feed.

• 1
  Compression spiralClean top and bottom edges on plywood and veneer.
• 2
  Chipload0.1–0.2 mm per tooth in hardwood at 16,000–20,000 rpm.
• 3
  Finishing pass0.2–0.5 mm at full speed for a glue-ready edge.

A 3-axis router moves the tool in X, Y, and Z only. It handles flat panels, cabinet parts, signs, and any profile that can be cut from one side. Setup is simple and cycle time is predictable. For 80% of wood parts, 3-axis is the right answer and adding axes just adds cost.

A 5-axis machine adds two rotary axes, so the tool can approach the workpiece from any angle in one setup. That matters for chair arms, sculpted furniture components, and mold masters with undercuts. The tool can also be tilted to keep the cutting angle constant along a curved surface, which reduces grain tear-out on complex shapes.

The trade-off is programming time. A 5-axis toolpath needs collision checking and a post-processor tuned to the machine. A simple part that takes 20 minutes to program for 3-axis can take two hours for 5-axis. If the part can be reached from two sides, two 3-axis setups are usually cheaper than one 5-axis setup.

GreatLight runs 16 simultaneous 5-axis machining centers with travels up to 4,000 × 400 × 150 mm, alongside 27 three-axis machines. For wood work, the choice is driven by geometry, not by which machine is free.

• 1
  3-axisFlat panels, profiles, and parts reachable from one side.
• 2
  5-axisSculpted forms, undercuts, and constant-angle finishing.
• 3
  Cost driverProgramming and setup time, not spindle time alone.

Hardwoods like oak, maple, walnut, cherry, ash, and beech machine cleanly with sharp tooling. They hold threads poorly though. A 1/4-20 screw pulled straight out of walnut will strip at low load. For structural joints, use threaded inserts or through-bolts with washers.

Softwoods such as pine and cedar cut fast but compress easily. Clamping pressure leaves dents that show up after finishing. Use soft jaws or cauls, and keep clamp pressure just enough to stop movement.

Engineered panels behave differently again. MDF cuts to a fine, uniform edge and takes paint well, but it is dense and abrasive. It dulls carbide faster than oak. Plywood has glue lines that chip if the cutter is dull. HDF machines like MDF but is harder on tooling. Particleboard is for concealed structure only, not visible edges.

Exotic hardwoods like teak, ipe, and wenge contain silica and oils. They cut well with carbide but wear it fast, and the oils can interfere with glue and finish adhesion. Wipe with solvent before bonding.

Whatever the species, let the material equalize in the shop for 24–48 hours before machining. Cutting cold or damp stock and then moving it into a dry room is the most common cause of a part that fits on the bench and fails in the field.

• 1
  Oak, maple, walnutClean cuts; use inserts for structural threads.
• 2
  MDF and HDFUniform edges; abrasive, dulls carbide faster.
• 3
  Teak and wengeOily and siliceous; wipe before bonding.

Metal shops quote ±0.005 mm. Wood does not work that way. The material itself moves more than that between morning and afternoon. Realistic wood tolerances sit in a different range, and quoting metal numbers on a wood part sets the job up to fail.

For a stable hardwood in a climate-controlled shop, ±0.1 mm on a routed profile is achievable with a finishing pass and a sharp tool. On a 1,000 mm panel, ±0.5 mm across the length is a fair target because thermal and moisture movement dominates. Hole positions in a panel can hold ±0.2 mm if the panel is clamped flat and the stock is dry.

Surface finish follows a similar logic. A sanded hardwood face can reach Ra 1.6–3.2 μm. MDF can go finer, Ra 0.8–1.6 μm, because there is no grain to tear. Anything below Ra 0.8 μm on wood is a coating result, not a machining result.

The practical rule: design for clearance, not for press fits. Wood joints should have 0.1–0.2 mm of clearance and rely on adhesive or fasteners for strength. If your design needs a metal-grade fit, the part should probably be metal.

GreatLight machines wood on the same 5-axis platforms used for metal, so we can hold tight numbers on the machine. The material sets the real limit, and we will tell you where it is.

• 1
  Profile±0.1 mm on stable hardwood with a finishing pass.
• 2
  Panel length±0.5 mm over 1,000 mm due to moisture movement.
• 3
  JointsDesign 0.1–0.2 mm clearance; do not press-fit wood.