A Basic Guide to Wood Properties for CNC Machining

Wood Properties for CNC Machining
Jack Lie CNC machining expert

Specialize in CNC milling , CNC turning, 3D printing, urethane casting, rapid tooling, injection molding, metal casting,


CNC machining can be used to manufacture a wide range of products, including those made from wood. In CNC machining wood, a block of wood is placed into a CNC machine, and a tool (such as a router or a lathe) is used to cut and shape the wood according to the instructions provided by the computer program. This process allows for the precise and efficient production of complex shapes and designs, and can be used to create a wide range of wood products, from furniture and cabinetry to musical instruments and crafts.

To optimize the cutting process for ultimate efficiency, there are lots of crucial factors needed to take into consideration. Here, we’ll specify the types of wood and important factors in the CNC machining process.

Types of Wood Available for CNC Machining

Hardwood

Hardwood is a type of wood that comes from deciduous trees, which are trees that lose their leaves annually. Hardwoods are generally denser, more durable, and more expensive than softwoods, which come from coniferous trees. Some examples of hardwood trees include oak, maple, and cherry. Hardwoods are commonly used in furniture, flooring, and decorative woodworking projects. They are also used to make a variety of products such as paper, veneer, and wood pulp.

To cut hardwood with a CNC machine, a computer program is used to input the desired design and the CNC machine uses a variety of cutting tools, such as routers or end mills, to cut the hardwood to the desired shape. The hardwood is typically secured to the bed of the CNC machine and the cutting tool is mounted on a movable arm. The arm moves the cutting tool over the surface of the hardwood according to the instructions in the computer program, creating precise cuts with a high level of accuracy.

Softwood

Softwood is a type of wood that comes from coniferous trees, which are trees that bear cones and have needle-like or scale-like leaves. Softwoods are generally less dense, less durable, and less expensive than hardwoods, which come from deciduous trees. Some examples of softwood trees include pine, spruce, and fir. Softwoods are commonly used in construction, as they are strong and easy to work with. Softwood is used to make furniture, or is mostly used for paper products, doors, and window panes.

The chart below concludes the Janka hardness of twenty common kinds of wood.

Janka hardness of 20 types of woods

Name Janka Imperial Hardness
Balsa 90
Buckeye,Yellow 350
Willow, Black 360
Pine, Sugar 380
Cottonwood, Eastern 430
Chesnut, American 540
Pine, Red 560
Douglas-Fir, Interior North 600
Birch, Gray 760
Ash, Black 850
Cedar, Eastern Red 900
Cherry, American Black 950
Walnut, Black 1010
Beech, American 1300
Oak, White 1360
Maple, Sugar 1450
Apple 1730
Cherry, Brailian 2350
Olive 2700
Rosewood, Indian 3170

The specific cutting tools and techniques used to cut softwood with a CNC machine may vary depending on the type and thickness of the softwood, as well as the desired finish. In general, softer woods may require the use of sharper cutting tools and slower cutting speeds to prevent tearing or splintering of the wood.

Engineered Woods

Engineered wood, also known as composite wood, man-made wood, or manufactured board, is a type of wood product that is made from wood fibers, particles, or strands that are bound together with a resin or other bonding agent. There are several types of engineered wood, including plywood, particle board, and fiberboard.

  • Plywood is made from thin layers of wood veneer that are glued together with the grain of each layer running at right angles to the one next to it. This gives plywood its strength and makes it less prone to warping and splitting than solid wood.
  • Particle board is made from wood chips, shavings, and sawdust that are mixed with a resin binder and pressed into sheets. It is a low-cost alternative to plywood, but it is not as strong or durable.
  • Fiberboard is made from wood fibers that are mixed with a resin binder and formed into sheets. It is available in various densities and is used for a wide range of applications, including flooring, cabinetry, and furniture.

Engineered wood products are generally less expensive than solid wood and are often used as a substitute for solid wood in construction and other applications. They can also be more stable and easier to work with than solid wood, as they are less prone to warping, splitting, and shrinking.

The CNC machine can be programmed to make a wide range of cuts, including straight lines, curves, and complex shapes. It can also be programmed to make multiple copies of the same design. The precision of the cuts and the ability to mass-produce parts make CNC machines an efficient and cost-effective method for creating engineered wood products.

What Should Be Taken Into Account of CNC Woodworking?

Due to unique properties of different types of woods, there are several factors to consider when using wood for CNC machining:

  1. Density
    Harder and denser woods are more difficult to machine, as they require more cutting force and produce more wear on the cutting tools. Softer and less dense woods are easier to machine, but they may not be as strong or durable.
  2. Strength
    The strength of wood varies depending on the species, grain direction, and moisture content. It is important to consider the strength of the wood when designing parts that will be subjected to load or stress.
  3. Stability
    Wood is a hygroscopic material, which means it absorbs and releases moisture from the air. This can cause wood to expand and contract, leading to dimensional changes. It is important to consider the moisture content of the wood and the relative humidity of the machining environment to ensure dimensional stability.
  4. Machinability
    Some woods are easier to machine than others due to their physical and mechanical properties. For example, softwoods are generally easier to machine than hardwoods, but they may not be as strong or durable.
  5. Finish
    The surface finish of the wood can be improved by using sharp cutting tools and applying a finish after machining. Sanding and applying a finish can also help to seal the wood and protect it from moisture.
  6. Tooling
    The choice of cutting tools is important when machining wood. High-speed steel (HSS) and carbide tools are the most commonly used for wood machining. HSS tools are less expensive and can be used for softer woods, but they are not as durable as carbide tools, which are more expensive but can be used for a wider range of woods.
  7. Moisture Content (MC)
    Moisture content (MC) is one of the most crucial factors to take into account when processing wood. A common problem with building anything out of wood is its incline to warp. Moisture changes in the air certainly affect the moisture content in wood. Any change in moisture content (whether it grows or reduces) will have an impact on the structure of the workpiece. This is why you’re expected to consider what type of moisture the product will be exposed to where it will ultimately be placed.
  8. Knots
    A knot is a branch or part of a branch that has been incorporated into the trunk. The mechanical properties of wood are affected by knots as a result of the interruption of the continuity and the change of direction of the wood fibers related to them. These properties are lower in this part of the wood as the fibers around the joints are twisted, causing stress concentrations. During the drying process, “checks” (cracks due to shrinkage) often occur around the knots. Strength and hardness perpendicular to the grain are exceptions to lower mechanical properties in general. Because of the latter two exceptions, to avoid shock loads, it’s recommended to reduce woodworking parameters when dealing with knotted parts of the workpiece.
  9. Grain Size
    Wood with large cellulose fibers refers to as coarse-grained (oak and ash) and wood with smaller and fewer fibers are called fine-grained (pine and maple). Softwood is often fine-grained and is therefore shaped to be easier to process because they don’t contain so many strong fibers to cut. It is worth noting that not all softwood trees are fine-grained and not all hardwood trees are coarse-grained.

Work with Runsom for Your CNC Woodworking Projects

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