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Home > Weapons > Woods for Training Weapons
by James Goedkoop <Send E-mail to Author>

The following is the first chapter of a book in process, titled "Bokken, Jo, and Related Wooden Weapons." Other chapters cover the design of various weapons used in Aikido training including observations on wooden swords and their schools of origin.


Introduction

The qualities that define the character of Bokken, Jo and other traditional Japanese wooden weapons, rest entirely on the integrity of the material itself. There are hundeds of wood choices overall and many regional varieties worthy of consideration but as we shall see in this section there are actually very few that are well suited for all situations that martial artists encounter in their weapons training.

The Japanese have always used their native evergreen white oak (Shiro Kashi) for most training weapons used in paired practice where there is likelyhood of impact with a partner's wooden weapons or armor. Kashi isn't generally considered a "fine" wood but its tough, reliable, relatively dense character is well suited for impact tool handles and martial art equipment. Many other materials and wood species are available in Japan. Unique weapons of unusual construction and materials, including several superb tropical varieties, are produced but only intended for settings appropriate to their scarcity, cost and appearance. Centuries of practical wisdom support this distinction between the utilitarian and the formal as it relates to martial art weapons.

The extension of the Japanese martial arts to other parts of the world, where no native tradition exists in the manufacture of related practice equipment, fosters attempts to produce traditional wooden swords and the like without the benefit of any accumulated local wisdom or reliable material from local sources. Because of this, there has been a tendency of non Japanese to overlook a distinction which is taken for granted in Japan - the role of materials suitable for routine practice and that of materials which are appropriate for presentation and ritual. Instead, many foreign practitioners view all equipment on a purely "qualitative level" and perceive the value of one's practice as being influenced by the degree of beauty and precision of the weapon - a notion generally discouraged by both Japanese and non Japanese masters and one, I think, that remains an obstacle in the development of weapons training. The following section is intended to guide the reader to an understanding of various materials and their appropriate use.

For both the utilitarian and refined, the wood is the weapon. Its strength, density, stability, color and texture are the potential for quality. Although a mediocre weapon may come from an exceptional piece of wood, it will always have within it the possibilities dictated by the the quality of the material. No amount of artistry will make a good practice weapon out of a mediocre piece of wood.

As it turns out, there are very few kinds of wood that are suitable for wooden weapons, especially ones longer than two feet or so where density and shock stength are important. Most hardwoods, especially the dozens of commercial species including native oak, maple, cherry, walnut etc. have mechanical drawbacks and most modern synthetic materials are not esthetically or historically appropriate to the traditional martial arts. It is little surprise that the materials chosen in this situation are not often seen in common woodworking where so many other readily available options exist.

The descriptions and information here include factual data concerning wood selections based on the production of thousands of wooden weapons for Japanese martial arts, published information and actual tests of hundreds of wood samples subjected to the stresses expected in paired practice.

It is necessary to categorize information and the following study, like all others, combines individuals of a species as if they were one but actually reflects an average of many unique members. In the case of natural wood there are significant differences within a species and the reader should consider the diversity: For example, American Black Walnut in general doesn't have suitable shock strength or dent resistance for this application and we would be tempted to unequevically extend this judgement to all Black Walnut. Under some (rare) conditions however, an individual tree may produce lumber that will produce a servicable and perhaps an excellent practice weapon. Several of the true hickories from a specific region (which will be discussed later) yield excellent quality lumber in general but an individual piece may be weaker than unusually good piece of material from an "inferior" species.


Impact Strength

Whereas the quality of wood can be described from many perspectives, one of the primary concerns here is its safety and strength during contact which typically occurs with sudden impact. The following chart, Impact Strength of Materials, shows the strength of various materials when subjected to impact shock (with other wood) expected during paired practice. The test uses a simple spring loaded ram* to test samples of identical size. The sole purpose of the test is to determine if a particular material has potential as a martial art weapon but some wood species are included to provide comparative data even if they would not qualify for other reasons.

(For those interested in the physics of the test: The strengh of natural woods (used as structural members) is well documented in published data where samples are subjecting to slowly applied loads. This test however is specifically designed to test shock strength as it relates to martial art practice. A hardwood ram, attached to a fiberglass spring, impacts equal sized test samples on the tangential surface. The spring's deformation is proportional to the magnitude of the applied force. The impact energy is calculated according to the relationship E=1/2ky2. Impact energy can be represented as the square of the calibrated distance that the spring is deformed. Samples are subjected to gradually increasing impacts until failure. The numerical values on the chart represent the impact energy that broke the sample. Most values are the average of five or more samples of the same species. )

White pine is included for reference. American White and Red Oak, both ring porous hardwoods, might have sufficient strength but their open grain presents exposure to damage in those areas.

In many cases, very hard and heavy hardwoods such as African Ebony prove to be relatively brittle. Other exotic species such as Greenheart,Blackheart, Blackwood, Leadwood etc all tend to have excellent resistance to denting but low shock strengh. These materials would show little damage at lower impacts but might break unexpectedly with a higher impact. Lignum Vitae, a wood with extraordinary properties, invariably develops checking (either superficial or more severe cracking) due to atmospheric humidity swings and its use a martial art weapon would not prove to be a wise use of resources.

Impact Strength Graph
Click image for an enlarged view of the impact strength graph
and included footnotes
or
click here for an Adobe Acrobat .pdf version.


Density

Along with impact strength, wood density is a key consderation in weapon quality. It is usually measured as a ratio called specific gravity. When wood floats in water, its specific gravity is less than 1 but there are a few varieties, mostly of tropical origin, that have specific gravities greater than 1 and will sink. High density does not necessarily translate into high impact strength. There are several dense woods that have a much lower impact strength than other less dense ones as shown below. Please review the information in the above chart "Impact Strength of Materials" and included footnotes which describe the impact test and clarify the data in the following table.

Wood Specific Gravity Impact Strength
White Pine .35 86
African Ebony 1.10 110
Red Oak .63 169
Purpleheart .79 173
Pau Ferro .73 173
Shiro Kashi (Japanese White Oak) .82 179
Honduras Rosewood 1.00 189
White Ash .60 196
Birch .62 196
KWW Laminated Composite 1.30 198
Coromondel Ebony 1.10 202
Osage Orange .80 243
Impact Grade Hickory .775 345

Although high density doesn't necessarily translate into high impact strength, it has a major influence on performance and maneuverability. It is almost always desirable for Baton (police stick) , Yawara (¡short stick ~12"), Kobuton (hand weapon ~5"), Tanto (wooden knife) and other short sticks under 24 inches. The additional inertia is a major benefit in many defensive situations and when the weapon is used for pressure point techniques, dense and harder wood is much more efficient. For these applications, wood with specific gravity over 1 is often best.

Bokken (wooden sword) and other longer weapons used in paired practice should be chosen from a material with high impact strength. In some cases, a wooden sword is intended to approach the actual weight of a real sword and higher density materials (specific gravity greater than 1) are required but these weapons should not be used for routine practice. Suitable higher density materials are almost always costly. Most wood with high specific gravity is tropical in origin (the laminated composite shown in the charts comes from reasonably well managed domestic sources but is expensive nonetheless). The most important consideration of all is the possibility of an impact which exceeds the material's shock strength; a situation that becomes more likely with a weapon over 24" in length and relatively slender in diameter like Bokken and Jo. High density materials are harder, with the appearance of being practically indestructable and sometimes won't show damage prior to failure. An unexpected, complete break may create a dangerous situation. The same precautions are advised for very long weapons including Bo (long staff ~ 72") , Naginata (Japanese halberd like weapon ~ 96"), Yari (spear up to 120"), Juken (rifle/bayonet ~ 72") etc. if used in contact with other practice weapons.


Materials

Different materials are appropriate for different weapons and different situations. The following wood selections are described and recommended according to their individual properties:

Shiro Kashi (Japanese White Oak)

Martial artists familiar with Japanese wooden weapons frequently refer to this wood simply as "White Oak". It has a tight but coarse grain structure and like North American White Oak, it has prominant rays which give it a distinctive figured appearance. It's either bone white or light tan in color and darkens over time. Shiro Kashi differs in several respects from North American White Oak. While related, the Japanese White Oak tree is evergreen and owing to its continuous growing season, does not have a conspicuous open grain like American White and Red Oak. Open grain structure, typical of the so called "ring porous" hardwoods presents soft areas which are more prone to impact damage. Kashi is uniformly hard, has excellent dent resistance and has better impact strength than American Oaks. There are two drawbacks relevant to its use in wooden weapons: It is not stable; weapons of Shiro Kashi will frequently warp due to changes in atmospheric humidity. Also, like other Oaks, it seems to lose strength as it ages. In tests conducted on older samples from wood that had been very strong, the aged material had lost its integrity substantially. The older wood will appear dry and develop cracks usually beginning with a grain separation in areas of repeated impact - a sure sign that the weapon is weakening. Clearly, Shiro Kashi should be considered a good quality utility wood, excellent for several years practice but probably having a limited life span.

White Ash

The most well known and useful of the Ash family is White Ash. The wood is strong in comparison to its weight and is often used for baseball bats, tool handles, oars and paddles. Ash is noted for its stability. It is less subject to twist, warp and dimensional change than most North American hardwoods.

Ash is a ring porous hardwood with strongly contrasting spring and summer wood. This characteristic results in alternate, relatively hard sections with softer areas of open grain. Because of this, Ash is more prone to objectionable denting when impacted on its softer areas and is not ideally suited for weapons taking direct impact. Because of its otherwise excellent mechanical properties however, and its tendency to get smoother and improve with continuous handling, it is one of the very best materials for long shaft sections on Yari and Naginata.

Birch

Birch is moderately heavy and hard with good strength. Its appearance is very similar to Maple with an even, fine texture and tight grain structure. White Birch refers to the white sapwood of the species and Red Birch refers to the heartwood of the same tree. Birch grows throughout the hardwood forests of temperate latitudes and is an important commercial hardwood. Its high shock strengh and availabiliy in thick, long pieces, making it a good contender for wooden Bo staff. Naginata, Yari and Juken. In its natural state, its drawback is its tendency to show impact dents where contact is heavy.

Birch is well suited to the production of veneers, In the 1950s, the US Forest Products laboratory developed a process of drawing resin and dyes through veneer stock and laminating the wood layers under extremely high pressure to produce an enhanced composite product. This material is generically known as Compreg (compressed, impregnated wood). The variation referred to in this publication is the "Laminated Rosewood Composite" of Kingfisher WoodWorks.

Impact Grade Hickory :

There are at least 16 species of Hickory native to Asia, Central America and North America. Mixed hickories, appropriate for furniture and cabinet work, are obtainable in lumberyards throughout the United States. Varieties from New England, the Midwest, Great Lakes and Southwest, including the closely related Pecan Wood, produce lumber comparable in quality to many other North American hardwoods as shown in the preceding impact and density charts. For lack of a better description, the designation "Impact Grade" Hickory refers to a source of regional varieties selected according to subspecies from a small area in the Central Appalachians where trees are selected that yield wood with properties suitable for martial art equipment. Not only is the material unique mechanically, it is also handled much differently than cabinet grade lumber. Common grades of commercial hickory are grouped together. Commercially distributed hardwood is usually kiln dried and hickory, which is difficult to dry, is sawn into into standard 3/4" planks which allow accelerated dry kiln schedules. These thinner planks include (mechanically) inferior species of Northern and Western hickories with the added risk of structural damage caused by faster drying schedules. This special stock however, is cut into thicker slabs of the most premium material from a specific geographical area and slowly air dried. This resulting "Impact Grade Hickory" is either bone white or light reddish in color. It has a flat, graceful grain structure and a smooth texture with good density. Its shock strength exceeds all native and exotic species including the commonly used Japanese White Oak (Shiro Kashi). While Oaks appear to become brittle with age, Weapon Grade Hickory retains its toughness. Although heavy contact with very hard materials will cause some denting, normal practice with similar weapons will just create an unobjectionable patina. Even after years of heavy use, it is unlikely to snap into dangerous pieces. Ideally, the best Dojo choice would be the uniform use of this material for paired practice. It's safe, strong, attractive and comes from a domestic managed resource. Just as Kashi is the only wood used in Japan for practice weapons, American martial artists can look to this specially graded hickory as the optimal choice.

Laminated Rosewood Composite (LRC)

LRC refers to a limited, premium grade classification of densified hardwood composite. Made by laminating very thin layers of imbued birch veneer under enormous pressure, it has a stunningly beautiful dark Rosewood color with black highlights, is totally stable and takes a mirror finish.Weapons of LRC have several notable benefits. With a specific gravity of 1.3, its extremely high density and hardness make it ideal for smaller weapons where those qualities are so desirable. It comes from domestic sustainable sources and is an excellent substitute for rare tropical varieties. Since the intersticial spaces and microscopic conduits of the wood are filled with resin, there is little if any exchange of atmopheric moisture and hence no warpage. When skillfully worked, it holds perfect detail and when polished and buffed, will take a mirror like shine without any additional surface treatments. Because it is extremely dense, bokken made of LRC can achieve both the weight, proportion and balance of a live blade. It has excellent physical properties overall and, in the case of bokken, approaches the closest interpretation possible of a sword. It is however, an engineered material with properties different from natural wood and LRC items should be treated more like live edged weapons than those of natural wood. Since the material does not dent easily, it gives the impression that it is much stronger than any natural wood. As the tests show however, it's strength exceeds many of the strongest natural woods but not immensily so. It tends to be edge sensitive and an accidental drop onto concrete, which would just dent most natural woods may cause a more serious chip in the composite material. While there have been many natural wood bokken destroyed when hit with a composite weapon and at least one live steel blade, there have also been a few composite weapons broken and a few instances where a glancing blow at the very end of the point damaged a composite bokken. For these reasons, the LRC is not recommended for paired work involving contact but better reserved for suburi (individual) practice, silent sword techinques, presentation or other special situations.

The last consideration, as it relates to paired practice may be said of any of the very hard and dense materials in general: In a practice situation, many students use equipment that fits their means and their experience. Very hard and heavy wood will certainly do significant damage to the budget oriented weapons that many beginning students start out with. In the interests of safety and good judgement, it is best to engage in daily paired practice with materials that do not cause unnecessary damage to a partner's equipment.

African Ebony

Several tropical hardwoods including African Ebony are extremely hard and heavy but without notable impact strength. Also known as Cameroun and Gabon Ebony, this wood is jet black with occasional grey striping and is the familiar black wood formerly used on piano keys. Because of its density, outstanding hardness and ability to hold detail, it is excellent in small hand held weapons used to apply pressure. Along with other wood of tropical origin, Ebony comes from sources that aren't necessarily well managed, should be considered a limited resource and used judiciously.

Honduras Rosewood

There are several species of natural Rosewood with excellent density, strength, dent resistance and overall physical properties. Honduras Rosewood is usually a dark reddish tan sometimes with prominant streaks of black and purple. It has a beautiful, coarse swirling grain structure with color patterns varying from reserved to startlingly bold. Rosewood is not often available from sustainable sources in pieces suitable for solid construction larger items. Smaller Tanto, Kobuton, Yawara and similar works are often possible. Bokken and Jo of natural Rosewood are highly desirable and extremely rare. This material, like other tropical woods is not recommended for daily practice or casual use due to its scarcity and unique character.

Pau Ferro

South American Pau Ferro (Ironwood) has a beautiful dark tan color often including black streaks and graceful dark figure patterns. It has fine, dense grain with a very smooth surface texture. Pau Ferro, an exceptional and rare tropical wood, is occasionally available in pieces thick enough for solid piece bokken and jo and it makes excellent blade sections for Yari and Naginata intended for presentation and solo practice.

Purpleheart Wood

Purpleheart is available in thick pieces which allow for the construction of largest and longest solid piece weapons. It is sometimes possible to obtain it from managed sources and has some outstanding properties making it especially suitable for staff type weapons like jo, bo etc. It is very hard, and usually displays a straight, uniform grain structure with a somewhat coarse texture. It turns to a clear, brilliant violet upon exposure to light. Purpleheart is extremely stable and lends itself to long, slender weapons where a less stable material would usually develop noticeable warpage. Because it is extremely stiff in comparison to its weight, it gives the user an energetic feel of returning energy rather than absorbing it and for these reasons, could be considered a "conditional wood" - an excellent choice for some situations.

Coromandel Ebony

Also known as Macassar Ebony, this exceptional wood deserves special consideration among the natural woods available for the construction of wooden swords, staffs and martial art weapons. Because of its superb character, it conveys a unique and unmistakable feeling of presence. Coromandel is strong, hard, has a ideal weight with a fine dense texture. If skillfully shaped and finished, an alive almost reptilian quality emerges with predominantly black with tan figure patterns and occasional subtle but surprising hints of green and other colors. It is arguably one of the most beautiful of all woods.

Upon reading this description, it may be tempting to conclude that a fine weapon of Coromandel Ebony is the optimal personal choice for the serious student of the martial arts. Its unrestricted use however, would actually be inappropriate. Acquiring unique and rare weapons of limited natural resources often reflects the enthusiam of aspiring students where, due to the cost and scarcity of this material, is best reserved for special situations - a gift perhaps to a senior instructor from an appreciative dojo.

Osage Orange

No discussion of wood, selected for weight and strength, is complete without mention of Osage Orange, an unusual North American hardwood with a unique heritage. Indigenous to the American Southwest, the wood has a superb strength and was highly prized by Native Americans for archery bows and is still coveted by traditional bowyers. When freshly cut, it has a startling and unlikely bright yellow color which slowly turns to a subdued orange tan. The tree does not produce much of the dense, straight grained wood which has good mechanical properties. High quality lumber is very rare but the tree is certainly not endangered. Other studies of shock strength sometimes rate Osage Orange as the strongest of all woods. When used in longer weapons for paired practice it absorbs energy upon impact with a surprising springy feel.


Under the name Kingfisher Woodworks, James Goedkoop has produced thousands of practice weapons for aikido practice and the sword related martial arts.


This article was first printed in the May/June 1999 edition (Issue #63; Vol 13, No. 3) of Aikido Today Magazine and is reprinted with their permission.

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