Name Sycamore
Location Eastern North America
Texture/Grain Medium/Closed
Specific Gravity 0.49
Hardness Soft
Strength Medium
T/R Stability 6.4/5.0%

 

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1. Wood Botany

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he mechanical properties are those that affect the performance of the wood species and the ease with which you can work it. Is the wood sufficiently hard, strong, and stable for your project? Can you cut, assemble, and finish it easily? To answer these questions, refer to the appropriate categories in the chart of “Mechanical Properties of Wood” below. This chart includes the following categories.

 

SPECIFIC GRAVITY
Although
specific gravity is technically a physical property, it’s usually included with mechanical properties. It’s a reasonably reliable indicator of the wood strength and ease with which it can be worked. Woods with high specific gravities are generally stronger and more difficult to work.

STRENGTH
Because numbers so often make little sense when considered by themselves, I've given each species a simple comparative rating in these strength categories so you can instantly understand where it falls in the entire range. If you need the actual numbers, see the chart of "Relative Wood Strengths."

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The hardness is the ability of the wood surface to resist damage. This is an important consideration when choosing woods for projects that will be subject to abrasion or heavy use. Ratings: Very Hard, Hard, Medium, Soft, Very Soft.

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Strength is the sum of compressive strength and stiffness. These determine the amount of weight a piece of wood will safely support. Ratings: Very Strong, Strong, Medium, Weak, Very Weak

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"Bendability" or bending strength indicates both the ease with which a wood can be bent and the percentage of its strength it retains after bending. Ratings: Very High, High, Medium, Low, Very Low.
 

 
This is a simple "three-point" strength test for wood which, as it is set up, measures both the modulus of elasticity and the modulus of rupture for the species "greenheart." This test was performed at the University of Cambridge in England.

MOVEMENT AND STABILITY
Wood changes dimension tangentially (across flat grain) and radially (across quarter grain). This movement is measured by determining the percentage that wood shrinks from when it’s green (freshly cut) to completely dry. The lower the percentage, the less the wood moves and the more stable it is. Additionally, a big difference between tangential and radial movement indicates that the wood is susceptible to warping, twisting, and bowing.

WORKING CHARACTERISTICS
Before buying a wood species that you’ve never worked before, it helps to know how difficult it is to surface the wood with a hand plane or a thickness planer. Does it lend itself to strong glue joints? Is it incompatible with common finishes? These working characteristics depend on many factors. If the wood is extremely dense, it’s harder to cut. Irregular grain patterns make planning more difficult. The cell structure of some woods makes them prone to splitting and chipping. Waxy or resinous extractives interfere with cutting, gluing, and finishing. The chart of “Mechanical Properties of Wood” rates the following:

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The relative ease of working a wood species with hand tools

bullet

The ease of working it with power tools

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The tenacity with which common wood glues hold it together

bullet

The facility with which it accepts a finish

COMMON USES
Finally, nothing helps so much in deciding whether or not to use a wood species for a project as knowing how other craftsmen use the same wood.
 


In yellow birch (top), there is a large discrepancy between the tangential movement (8.1%) and radial movement (3.6%). Consequently, the species is prone to warping, twisting, and bowing. In Honduran mahogany (bottom), on the other hand, the discrepancy is very small (4.1% versus 3.0%). This wood is much more likely to remain flat. (modulus of elasticity). This is a concern when the wood must withstand high amounts of stress.*
 

Biodiversity Many useful wood species, especially those from fragile environments such as rainforests, are severely depleted from overuse and poor management. These are specified as “Endangered” in the Comments section of the chart of “Mechanical Properties of Wood.” This designation is determined by CITES (Council on International Trade in Endangered Species), the result of an international agreement an the conservation of species that began in 1973. You can search this list at:

CITES
International Environment House
11 Chemin des Anémones
CH-1219 Châtelaine, Geneva
Switzerland

You can find additional information on endangered wood species in the "Red List" from the International Union for the Conservation of Nature (IUCN) or the “Good Wood Guide” from the Friends of the Earth.


 


Sometimes you get lucky. Although there are 28,000 species of fauna on the CITES endangered list and as many as 970 species of trees thought to be headed for extinction, occasionally we get some good news. This is a Judean Date, Phoenix dactylifera, a long-extinct palm tree important in Biblical times as a source of food and medicine (see Psalms 92:12). The species was revived, at least for a short time, from a 2000-year-old seed found at the archaeological dig in Masada, Israel.

USING THE CHART
The chart of “Mechanical Properties of Wood” is divided into three parts -- North American Hardwoods, North American Softwoods, and World Woods, or woods from other places than North America. To access any part, click on the title below. To see the properties for any wood species, click on its name.
Tree Trivia:
North American Hardwoods
 
bullet Alder, Red
bullet Ash
bullet Aspen
bullet Basswood
bullet Beech
bullet Birch, Yellow
bullet Butternut
bullet Cherry
bullet Chestnut, Wormy
bullet Elm, Red
bullet Gum, Red
bullet Hickory
bullet Holly
bullet Maple, Hard
bullet Maple, Soft
bullet Oak, Red
bullet Oak, White
bullet Osage Orange
bullet Poplar, Yellow
bullet Sassafras
bullet Sycamore
bullet Walnut
bullet Willow

North American Softwoods

bullet Cedar, Aromatic Red
bullet Cedar, Western, Red
bullet Cypress
bullet Fir, Douglas
bullet Hemlock
bullet Pine, Eastern White
bullet Pine, Ponderosa
bullet Pine, Sugar
bullet Pine, Southern Yellow
bullet Redwood
bullet Spruce, Sitka

World Woods (Other Than North America)

bullet Balsa
bullet Bocote
bullet Bubinga
bullet Cocobolo
bullet Ebony, Gaboon
bullet Goncolo Alves
bullet Jelutong
bullet Lacewood
bullet Mahogany, African
bullet Mahogany, Honduran
bullet Mahogany, Philippine, Lauan
bullet Paduak
bullet Purpleheart
bullet Rosewood, Bolivian
bullet Rosewood, Honduran
bullet Rosewood, Indian
bullet Teak
bullet Tulipwood
bullet Wenge
bullet Zebrawood

The extraction of
salicin crystals from the bark of the Willow tree by
Johann Buchner in 1828 led to the discovery of aspirin.


Marking tall white pines in New England with a "broad arrow" to reserve them for the British Royal Navy. This imposition was one of many that led American colonists to revolt against Britain.


Redwoods are among the largest (350 feet tall) and oldest (2,200 years) living beings on the earth.


The resin of the Jelutong tree, a favorite of wood carvers, is tapped to make chewing gum.

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*Indicates that you can enlarge a photo by clicking on it. To reveal the information in a "Superphoto," first enlarge it and then move the cursor over it.

 "Abundant to all the needs of man, how poor the world would be without wood."
Eric Sloane in Reverence for Wood

 

Wood and Woodworking Materials/Hardwoods and Softwoods/Mechanical Properties,
part of the Workshop Companion,
essential information about wood, woodwork, and woodworking
necessary to woodworkers and practitioners of the wood arts
to become competent craftsmen.
By Nick Engler.

Copyright © 2009 Bookworks, Inc.