by Eric Meier
One of the hidden gems amidst the mountains of wood research and data that’s been done by the USDA and its Forest Products Laboratory is a study of machinability and workability of many common US hardwoods.
Working with Wood: down to a science
Most people are content with more or less anecdotal or somewhat subjective opinions of a given wood and how it behaves when being machined. A wood is either “good,” “bad,” or maybe even “excellent,” or “very poor” when it comes to workability. But what if you could quantify this data down to specific numbers?
What if you could perform different tasks on a wood species over and over, and come up with a precise number (or percentage) that represents exactly how likely the wood will machine or be worked with success? That’s exactly what the USDA study has done, and I’d like to share the results with you online in a format that allows for sorting and displaying averages to make the data even clearer.
Machinability of US Hardwoods
(% of pieces producing a satisfactory result)
|Common Name||Scientific Name||Overall|
|Cherry, black||Prunus serotina||89.6||80||80||88||100||100||–||–||–||–|
|Oak, white||Quercus alba||79.8||87||35||85||95||99||83||91||69||74|
|Oak, red||Quercus rubra||78.7||91||28||84||99||95||81||86||66||78|
|Maple, bigleaf||Acer macrophyllum||73.6||52||56||80||100||80||–||–||–||–|
|Walnut, black||Juglans nigra||71.5||62||34||91||100||98||–||78||50||59|
|Beech, American||Fagus americana||68.0||83||24||90||99||92||49||75||42||58|
|Chestnut, American||Castanea dentata||66.2||74||28||87||91||70||64||56||66||60|
|Maple, hard||Acer saccharum||64.0||54||72||82||99||95||38||57||27||52|
|Elm, soft||Ulmus spp.||63.8||33||13||65||94||75||66||74||80||74|
|Poplar, yellow||Liriodendron tulipifera||59.4||70||13||81||87||63||19||58||77||67|
|Alder, red||Alnus rubra||57.0||61||20||88||64||52||–||–||–||–|
|Tupelo, water||Nyssa aquatica||54.2||55||52||79||62||33||34||46||64||63|
|Maple, soft||Acer spp.||52.3||41||25||76||80||34||37||59||58||61|
|Tupelo, black||Nyssa sylvatica||50.2||48||32||75||82||24||21||42||65||63|
*Description for each category to qualify as producing a satisfactory result are as follows:
- Shaping—”good to excellent”
- Turning—”fair to excellent”
- Boring—”good to excellent”
- Mortising—”fair to excellent”
- Sanding—”good to excellent”
- Steam bending—”unbroken”
- Nailing—”free from complete splits”
- Screwing—”free from complete splits”
Making Sense of the Data
This data is by no means the last word on wood workability. But because it was done in a subjective and impartial way, it’s at least a good starting point in painting an overall picture of how hardwoods will respond to machining operations. By looking at the data as a whole, a few observations can be made.
1. Working with hand tools can be a lot different than machine tools
In the world of hand tools, there’s a very important metric that can be looked at to determine how a wood will respond to hand tooling operations: density. While not infallible, as woods get lighter in weight, they generally become easier to saw, carve, chisel, plane, etc. Conversely, uber-hard and heavy woods, especially many imported tropical hardwoods, can be a real bear to work with.
So when woodworkers see a list like this, the woods that are thought to be very easy to and cooperative to work with in the hand tool world may actually end up getting a less-than-ideal score. A good example of this would be basswood (Tilia americana) —generally regarded as a very good carving wood, and very easy to work with, yet it gets a fairly low score on the machinability front.
2. There’s a happy medium in wood weight as it pertains to workability
Taking black cherry (Prunus serotina) as our paragon of workability, we can do some rough comparisons to see what might make a wood well-suited for different machining tasks. Toward the bottom of the list seems to be wood that’s too light and soft. When this lightness is also combined with interlocked or irregular grain, it can make for a challenging time in the shop. This is reflected in woods like tupelo, willow, and aspen/cottonwood ending up at the bottom of the heap.
On the other end of the spectrum, especially among those that have worked with extremely dense imported hardwoods, there’s definitely a line that can be crossed where a wood becomes just too hard to work with using regular woodworking tools. While the list above is slightly skewed in favor of denser woods, it should be noted than none of the woods normally get above a density of around 50 lbs/ft3 (800 kg/m3). And while some heavy woods may produce clean results, they may require special treatment or may be very tough on the cutting edges, making their use less practical and not something taken into account in the bare numbers.
3. It may not be correct to give equal weight to each category
To be honest, the combining of all categories into a single average score was not something in the original study data. I only added this feature (as well as the ability to sort on different facets) afterward because it was so conducive to this digital medium.
But with nine different categories, the tests cover a broad range of potential situations that may or may not be pertinent to your situation. For instance, if you are doing more traditional woodworking (which generally eschews metal fasteners), then the values for nail splitting and screw splitting may not have much relevance to your situation.
On the other hand, an operation like planing is a nearly universal step in many woodworkers’ projects—and its a phase where machining defects like tearout will very often occur. In this way (whether by accident or intentionally), the columns in the table above are more or less sorted in order of most significant to least going from left to right. Despite this, the average of all categories represents a true, unweighted average of all recorded data.
4. Possible CNC router and other automated applications
As CNC (computer numerical controlled) routers, lathes, and other tools become more and more popular (and affordable), the list above may become increasingly relevant.
At the moment, most CNC work with different species is trial-and-error, and I’ve not been able to provide much specific advice in this burgeoning area of woodworking. Nonetheless, the list above has at least parsed out each individual facet of a wood’s workability, so perhaps with time a clearer picture can be drawn from the data as to what constitutes an ideal wood for CNC applications.