CNC Woodworking Without The Headaches

Wood is often seen as an easy-to-machine material, especially compared to metals. However, CNC woodworking presents unique challenges due to the natural variations in wood grain, density, and moisture content. Understanding these properties is crucial for optimising tool performance, minimising waste, and achieving clean, precise cuts.

Here’s a closer look at the key factors that affect CNC machining of wood and how to account for them.

Types Of Wood For CNC Machining

Wood is generally classified into three main categories: hardwood, softwood, and engineered wood. Each type behaves differently during machining, requiring adjustments in tool selection, cutting speeds, and feed rates.

1. Hardwood – Strong, Durable, and Versatile
Hardwoods come from deciduous trees (angiosperms) such as oak, ash, and birch. They are generally denser and more durable than softwoods, making them ideal for furniture, flooring, and construction components.

However, their density can make machining more challenging. Sharp tools, optimised feed rates, and correct cutter selection are essential to prevent burn marks or tear-out when machining hardwoods.

2. Softwood – Easier to Cut, but Not Always "Soft"
Softwoods come from coniferous trees like pine, spruce, and cedar and are widely used in joinery, furniture making, and construction. They are typically less dense than hardwoods, making them easier to machine, but the term "softwood" can be misleading.

Species like Douglas fir and European larch are denser and tougher than some hardwoods, requiring the right tooling and cutting parameters. Checking the Janka hardness scale ensures the best CNC setup for clean, efficient machining.

3. Engineered Wood – Consistent but Abrasive
Engineered wood, such as MDF (Medium-Density Fibreboard), plywood, and particleboard is made from wood fibres or particles bonded with adhesives. While these materials offer consistent machining properties, the resins and adhesives make them highly abrasive, leading to faster tool wear.

Using solid carbide & coated tools helps maintain sharp edges and prolong tool life when machining engineered woods.

Key Wood Properties That Affect CNC Machining

1. Grain Structure – Coarse vs. Fine-Grained Woods

Wood is a natural composite material, with strong cellulose fibres held together by lignin. The grain structure significantly impacts machinability:

Coarse-grained woods (e.g., oak, ash) have an open grain structure, which increases the risk of tear-out during machining.
Fine-grained woods (e.g., beech, birch) have smaller, more uniform fibres, allowing for smoother cuts and easier machining.

2. Moisture Content – The Biggest Factor in Wood Stability

Wood naturally absorbs and releases moisture from the air, which can cause warping or dimensional changes. Managing moisture content (MC) is essential for CNC precision and stability.

Ideal MC for machining: 8-12%, depending on the environment and application.
Too high MC (>12%) – Wood is softer and harder to cut cleanly, requiring lower spindle speeds and reduced feed rates. It can also increase tool wear due to interactions with resins, sugars, and tannins.
Too low MC (<8%) – Wood becomes brittle, increasing the risk of chipping and splintering.

3. Knots and Irregularities – A Machining Challenge

Knots are dense, irregular grain structures where a branch was once embedded in the tree trunk. These can disrupt machining by:

✔ Increasing tool wear
✔ Changing grain direction suddenly, causing tear-out
✔ Raising the risk of tool breakage due to their harder density

To prevent issues, reduce feed rates when machining near knots to avoid sudden stress on the tool.

Optimising CNC Cutting For Wood

To get the best results from CNC woodworking, follow these machining tips:

✔ Use Solid Carbide single flute or twin flute up spirals tools – Ideal for softwoods and MDF, they offer excellent chip evacuation and reduced heat buildup.
✔ Use down-cut or compression bits – Prevents tear-out on veneered plywood and laminated surfaces.
✔ Adjust spindle speed based on woods & engineered woods – Hardwoods, softwoods & Engineered Woods need to be cut at lower RPMs such as 18,000 rpm.

Always try to use a “ramp in” process on the toolpath so as to limit a vertical plunge that can create heat and generate scorching .
✔ Minimise tool dwell time – Reduces heat buildup and prevents burn marks on wood surfaces.

At Complete CNC Solutions, we supply high-performance CNC tooling optimised for cutting all types of wood. From solid carbide compression cutters to single or twin flute up-spiral carbide tools for engineered materials, we ensure you get precision, efficiency, and longevity from your CNC router.