Selecting the correct type of wood for a project is crucial for any woodworker or DIYer. The characteristics and properties of the wood determine how well it will perform for different applications.
One key factor to consider is the wood's hardness, usually measured using the wood hardness scale.
What Is the Wood Hardness Scale?
The wood hardness scale, also known as the Janka hardness scale, is a measure used to determine the resistance of a wood sample to wear and denting. It is an essential tool for woodworkers as it provides a standardised way of comparing the hardness of woods. The test involves measuring the force required to embed a .444-inch steel ball to half its diameter in wood, with the results stated in pounds-force (lbf).
The Janka scale gives an objective numeric value that helps compare the hardness between various wood species. Janka ratings are listed on a wood strength chart, showing that softer woods have lower ratings while harder woods have higher Janka ratings. For instance, balsa has a rating of just 90 lbf, making it the softest wood species, while Australian buloke has a Janka rating of 5060 lbf.
How Does Wood Hardness Impact Woodworking Projects?
Wood hardness has the following implications for woodworking:
Durability and Longevity
Harder woods are generally more resistant to wear, damage, and decay, making them ideal for high-traffic areas and outdoor projects. On the other hand, softer woods may show signs of wear more quickly.
Harder woods can be more challenging to cut, shape, and sand, potentially increasing the time and effort required to complete a project. In contrast, softer timber is usually easier to work with but can be more prone to damage during the woodworking process.
Tool Wear and Tear
Harder woods tend to dull blades and cutting tools more quickly, requiring frequent sharpening or replacement of tools. While they are gentler on tools, softer woods may need sharper blades to avoid tearing or crushing the wood fibres.
Joinery and Fastening
Harder woods may require pre-drilling to prevent splitting, but they typically provide stronger joints, whereas softer woods are more forgiving during fastening but may produce less durable connections.
When it comes to finishing, harder woods often stain and finish more evenly, but very dense woods may need special preparation for best results. Softer woods may absorb stain and finish unevenly, potentially requiring wood conditioner or other treatments to achieve a uniform appearance.
Cost and Availability
Harder timber is often more expensive and may be less readily available, depending on the species and region. On the other hand, softer woods are typically more affordable and widely available.
When to Choose Harder Woods
Woods with higher Janka ratings tend to perform well for projects that involve consistent impact or abrasion. Here are some typical uses for very hard woods:
Flooring: Hardwood floors need to handle heavy foot traffic daily. Dense woods like oak and maple stand up well to this pressure over time.
Cutting boards: Woods like teak and beech resist knife scratches, ideal for a kitchen cutting surface.
Tabletops: Durable woods prevent dents and liquid damage on dining tables that see daily use. Good options include opepe, makore, and jarrah.
Stair treads: Stairs experience concentrated foot impact in small areas. Hardwoods like ash or white oak are common stair materials.
Tool handles: Impact-resistant woods like hickory and hornbeam hold up to repeated strikes when used for hammer and axe handles.
When to Choose Woods with Medium Hardness
Woods with moderate wood hardness ratings offer a balance of workability and durability for many applications:
Interior furniture: Woods like cherry, walnut, and mahogany have enough hardness to resist scratches and indentations yet are pliable for carving and finishing.
Cabinetry: Woods in the 1000-1500 range on the wood scale like alder, poplar, and pecan machine well and accept different stains and finishes.
Turning blanks: Moderately hard woods provide sufficient sturdiness while remaining easy to shape on a lathe, like yellow birch, elm, and sycamore.
Shelving: Mid-range woods offer strength to hold items while resisting minor bumps and scrapes, like maple or red oak.
Trim and moulding: Woods that aren't too soft or too hard, like poplar or ash, make shaping and installing trim manageable.
When to Choose Softer Woods
On the lower end of the Janka scale, softer woods lend themselves to more delicate work where shaping and finishing are priorities:
Carvings: Low-density woods, like basswood and butternut, enable detailed carvings to be sculpted more easily. The wood holds crisp edges without splitting.
Musical instruments: Softwoods allow acoustic instruments to resonate properly. Options like spruce, cedar, and mahogany are common for guitar soundboards.
Moulding and millwork: Intricately shaped mouldings machine well when using softer species like pine or alder. The end grain accepts stain evenly.
Toys and models: Woods like balsa and paulownia are light and simple for children to saw and shape when making hobby projects.
Boxes and crates: Lightweight woods keep shipping costs down while providing protection against minor bumps. Popular choices are pine, spruce, and larch.
Working with a Range of Wood Hardnesses
A useful strategy when undertaking a woodworking project is to use a mix of wood species with different hardness levels suited for specific components.
For example, durable hardwoods might be ideal for structural frames, legs, or surfaces that need to withstand scratches. More moderate woods could be selected for drawers, cabinets, and interior parts that receive less wear, while delicate ornamental details and carvings may be made from softer woods that are easy to machine and shape.
Having a range of wood hardnesses provides the correct properties where you need them. The wood hardness scale helps identify those densities to match the woods with their intended uses.
Limitations of the Wood Hardness Scale
While the Janka wood hardness scale is an invaluable tool for woodworkers, it's important to understand its limitations.
It Only Measures One Property of Wood
The Janka scale only measures hardness, not other crucial properties like workability, grain pattern, or moisture resistance. A wood species may be hard according to the Janka scale, but it might also be difficult to work with due to its grain pattern or tendency to warp when drying.
Wood Is Tested in a Controlled Environment
The Janka test is conducted under controlled conditions, which may not reflect the real-world contexts in a woodworking shop. Factors like temperature, humidity, and the age of the wood can all affect its hardness, which are not accounted for in the Janka rating.
It Doesn’t Account for Variations Within a Species
Lastly, the Janka scale doesn't account for variations within a single species of wood. For example, the hardness can vary significantly between the heartwood and sapwood of the same tree or between trees grown in different climates.
Therefore, while using a hardness of wood scale can be a helpful starting point, it's essential to consider these limitations and supplement the Janka rating with additional research and hands-on experience when choosing wood for your projects.
Navigate Wood Hardness with Woodshop Direct
The wood hardness scale is a vital guide for every woodworker and DIY enthusiast.
Understanding wood hardness and using the Janka scale ratings to compare different species allows you to make informed selections when planning woodworking projects.
Woodshop Direct supplies a wide selection of timber species with different hardness levels to meet any need. Our woods are FSC and PEFC-certified, aligning with our commitment to sustainability and ethical sourcing.