Machinability of Domestic Hardwoods

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. 

Quartersawn sycamore guitar body with routed cavities

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 NameScientific NameOverall
Average
PlaneShapeTurnBoreMortiseSandBendNailScrew
Cherry, blackPrunus serotina89.6808088100100
TanoakNotholithocarpus densiflorus80.0803981100100
Oak, whiteQuercus alba79.8873585959983916974
Oak, redQuercus rubra78.7912884999581866678
PecanCarya spp.76.188408910098784769
Maple, bigleafAcer macrophyllum73.652568010080
Walnut, blackJuglans nigra71.562349110098785059
AshFraxinus spp.71.0755579945875676571
HickoryCarya spp.70.27620841009880763563
HackberryCeltis occidentalis69.07410779972946363
Beech, AmericanFagus americana68.0832490999249754258
Chestnut, AmericanCastanea dentata66.2742887917064566660
BirchBetula spp.64.4635780979734723248
Maple, hardAcer saccharum64.0547282999538572752
Elm, softUlmus spp.63.8331365947566748074
MagnoliaMagnolia spp.60.6652779713237857376
SweetgumLiquidambar styraciflua60.3512886925823676969
Poplar, yellowLiriodendron tulipifera59.4701381876319587767
SycamorePlatanus occidentalis57.3221285989621297974
Alder, redAlnus rubra57.06120886452
Tupelo, waterNyssa aquatica54.2555279623334466463
Maple, softAcer spp.52.3412576803437595861
WillowSalix spp.50.952558712424738962
Tupelo, blackNyssa sylvatica50.2483275822421426563
CottonwoodPopulus spp.48.821370705219448278
BasswoodTilia americana48.364106876511727968
AspenPopulus spp.47.2267657860

*Description for each category to qualify as producing a satisfactory result are as follows:

  • Planing—”perfect”
  • 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.

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