All about wooden weapons - a new article

[charles]

In response to changes in relative humidity, wood expands and contracts. There is no stopping this reaction. Applied finishing materilas, at best, slow the change in size and shape, but do not prevent it.

In general, wood does not expand or contract equally in all directions: it is an "anisotropic" material. The unequal response is what results in splitting and deformation of shape - twisting and cupping. For the purposes of analysis, three directions or orientations are defined: linear, along the length of the fibers of the wood; radial, from the center of the tree outwards, and; tangential, around the circumference of the tree. Wood always expands and contracts least along the length of its fibers/"grain", so little as to be negligible in most applications. The concern is its radial and tangential expansion and contraction.

These two websites gives an overview of the terms: http://workshopcompanion.com/KnowHow/De ... vement.htm
http://www.popularwoodworking.com/trick ... -expansion

Average values are tabulated for the % change in size, in both radial and tangential directions, for many species of wood. These indicate that for a specific width of board, cut with a specific grain orientation (e.g. flatsawn vs. quartersawn) you can expect the tabulated % change in size for each change in wood moisture content of 1 %. The smaller the per cent change, the less the wood will expand or contract. The ratio of radial to tangential change is also tabulated and provides a measure of how likely the wood's shape will distort in response to changes in relative humidity.

With that background, Dalbergia sissoo, commonly called Northern Indian rosewood, Sissoo or Shesham, has R, T and T/R values of 3.1%, 5.1% and 1.8, from http://www.wood-database.com/sissoo/.

Dalbergia latifolia, commonly called East Indian rosewood, has R, T and T/R values of 2.7%, 5.9% and 2.2, from http://www.wood-database.com/east-indian-rosewood/. East Indian rosewood is one of the most common materials from which guitar backs and sides are made - as well as fingerboards and bridges. It is considered a relatively stable wood.

Comparing the values of sissoo and latifolia, they aren't hugely different and have similar stability to changes in moisture content. (Compare that, for example, with Lignum Vitae, at 5%, 8% and 1.8, or Gabon ebony, used for centuries in instrument making, at 8.3%, 11.2% and 1.3. It is common to see cracked ebony fingerboards, for example.)

The numbers above give a general indication of what to expect, useful for determining how a finished wooden article will behave to changes in humidity. However, if the wood is properly dried before being made into finished objects and the grain orientation of those objects chosen to minimize wood movement, the effects of changes in humidity on the finished objects can be minimal.

Guitars have a variety of specific issues. One issue is that the large, thin wooden surfaces of the top and back are fixed in size all around their edges: they are constrained, preventing expansion and contraction of the overall size of the top or back. The result is that when a guitar top or back is subject to high humidity, the top or back bows to increase its size, since it cannot increase its perimeter. When a guitar top or back is subject to low humidity, it shrinks. The top or back can only shrink to a flat surface, providing the shortest distance across its width. When the forces causing shrinkage exceed the strength of the wood fibers, the top or back splits to relieve those forces. An unconstrained wooden sword, for example, will not have that issue. Movement across the width of a guitar top or back is minimized by using quartersawn (vertical grain) wood. It has now become popular - with increasing scarcity of "good" wood - to use flat sawn wood for backs and sides. Doing so increases their risk of cracking, if the humidity of the wood is not maintained.

So, in short, the sissoo will probably work quite well for wooden weapons, and guitars, if the wood is properly dried prior to making the weapons and has its grain oriented to suit the specifics of the finished wooden object. (For guitars, the ideal grain orientation is quartersawn, not possible unless the tree is at least 16+ inches in diameter, or the top or back is made of more than 2 pieces. For weapons, such as swords, the ideal grain orientation might be "rift" sawn, by definition, neither quartered nor flat sawn.)


EDIT:

Some examples of sissoo for use in guitars:
http://rctonewoods.com/RCT_Store/indian ... od-c-1_38/
http://www.vorreiterguitars.com/?page_id=804

[jonathan.bluestein]

Thank you for this wonderfully thorough and enlightening answer!

Are you sure the first link is for Sissoo guitars? I think they're all Dalbergia Latifolia there at the moment.

The second link does look like it, but I would guess the wood is quite old. During at least the first few years, from many projects I've seen and from my own wood, the grain is much brighter brown, in the beginning sometimes even a little reminiscent of Cocobolo. The wood of the piece in the second link appears almost black, and reminiscent of African Blackwood.

This is the color I usually get:

[charles]

You're welcome.

In the first link, the photos are of Indian Rosewood: I linked to it for the description/comparison of Indian and Sissoo.

The photos in the second link do look very dark, though they don't show the back or sides very well. I'm just assuming that the guy who made it knows what he used: he may also have stained it. My point was simply, there are people selling Sissoo specifically for guitar parts and there are people making guitar parts out of it. There are other links that I didn't post for fingerboards etc. out of Sissoo.

The beauty - and challenge - of wood as a material is that is can vary so much in color and grain from one piece to the next, even within the same species. The photo you linked does look a lot like some freshly cut cocobolo, also of the rosewood family. Many woods will darken considerably when exposed to air and/or sun. Padauk, for example, will go from bright orange to dark brown when subject to UV light. Cocobolo will also darken considerably over time, often to a dark brown from its initial orangey brown.

You probably already know this, but make sure the ends of your boards are fully sealed - painted or paraffin waxed. They'll likely split no matter what you do, but sealing the ends will reduce that considerably. Think of the structure of wood as a handful of drinking straws. Moisture travels most readily through the center of straws. Sealing the ends of the straws reduces the rate at which moisture escapes through the ends, allowing more even drying between ends and sides. The more even the drying, the smaller the stresses, the less warpage and splitting.

If your logs were cut end-to-end like a load of bread, in slices, you'll get one or two pieces that are near quarter sawn, one or two that are flat sawn and the rest rift sawn. If you pay attention to the orientation of the end grain (annual rings), you'll see differences in the orientation effects how each board shrinks/warps. Is the photo of the wood you have drying, or just a photo similar to what you have?

[Niall Keane]

I assume the pore issue is what makes White oak not suitable for outdoors? We use English oak etc. for such.

White oak is "often" used for outdoor purposes, where it weathers well to a silver gray. It is often used as a modern alternative to teak or ipe. There is a historic building just up the street from me. It was recently restored and a modern addition was created. Interestingly, the outside framing members, between large windows, are all unfinished white oak. Of course, white oak is one of the woods of choice for wine and scotch making, staying in contact with moisture for long periods of time. It does have its exterior uses where one wants that weathered look.

not common in the UK and Ireland. wish I'd known what you say above some years ago when it was insisted upon by a Joinery and Carpentry company that English oak be used externally and I had a whole load of hassle trying to match as close as possible the tones. Admittedly I was treating it (oil) to retain its fresh look, perhaps that was a factor in their advice? Still it was looking ok a year later:



Anyway I digress, this is a martial arts forum.

[Niall Keane]

In response to changes in relative humidity, wood expands and contracts. There is no stopping this reaction. Applied finishing materilas, at best, slow the change in size and shape, but do not prevent it.

In general, wood does not expand or contract equally in all directions: it is an "anisotropic" material. The unequal response is what results in splitting and deformation of shape - twisting and cupping. For the purposes of analysis, three directions or orientations are defined: linear, along the length of the fibers of the wood; radial, from the center of the tree outwards, and; tangential, around the circumference of the tree. Wood always expands and contracts least along the length of its fibers/"grain", so little as to be negligible in most applications. The concern is its radial and tangential expansion and contraction.

These two websites gives an overview of the terms: http://workshopcompanion.com/KnowHow/De ... vement.htm
http://www.popularwoodworking.com/trick ... -expansion

Average values are tabulated for the % change in size, in both radial and tangential directions, for many species of wood. These indicate that for a specific width of board, cut with a specific grain orientation (e.g. flatsawn vs. quartersawn) you can expect the tabulated % change in size for each change in wood moisture content of 1 %. The smaller the per cent change, the less the wood will expand or contract. The ratio of radial to tangential change is also tabulated and provides a measure of how likely the wood's shape will distort in response to changes in relative humidity.

With that background, Dalbergia sissoo, commonly called Northern Indian rosewood, Sissoo or Shesham, has R, T and T/R values of 3.1%, 5.1% and 1.8, from http://www.wood-database.com/sissoo/.

Dalbergia latifolia, commonly called East Indian rosewood, has R, T and T/R values of 2.7%, 5.9% and 2.2, from http://www.wood-database.com/east-indian-rosewood/. East Indian rosewood is one of the most common materials from which guitar backs and sides are made - as well as fingerboards and bridges. It is considered a relatively stable wood.

Comparing the values of sissoo and latifolia, they aren't hugely different and have similar stability to changes in moisture content. (Compare that, for example, with Lignum Vitae, at 5%, 8% and 1.8, or Gabon ebony, used for centuries in instrument making, at 8.3%, 11.2% and 1.3. It is common to see cracked ebony fingerboards, for example.)

The numbers above give a general indication of what to expect, useful for determining how a finished wooden article will behave to changes in humidity. However, if the wood is properly dried before being made into finished objects and the grain orientation of those objects chosen to minimize wood movement, the effects of changes in humidity on the finished objects can be minimal.

Guitars have a variety of specific issues. One issue is that the large, thin wooden surfaces of the top and back are fixed in size all around their edges: they are constrained, preventing expansion and contraction of the overall size of the top or back. The result is that when a guitar top or back is subject to high humidity, the top or back bows to increase its size, since it cannot increase its perimeter. When a guitar top or back is subject to low humidity, it shrinks. The top or back can only shrink to a flat surface, providing the shortest distance across its width. When the forces causing shrinkage exceed the strength of the wood fibers, the top or back splits to relieve those forces. An unconstrained wooden sword, for example, will not have that issue. Movement across the width of a guitar top or back is minimized by using quartersawn (vertical grain) wood. It has now become popular - with increasing scarcity of "good" wood - to use flat sawn wood for backs and sides. Doing so increases their risk of cracking, if the humidity of the wood is not maintained.

So, in short, the sissoo will probably work quite well for wooden weapons, and guitars, if the wood is properly dried prior to making the weapons and has its grain oriented to suit the specifics of the finished wooden object. (For guitars, the ideal grain orientation is quartersawn, not possible unless the tree is at least 16+ inches in diameter, or the top or back is made of more than 2 pieces. For weapons, such as swords, the ideal grain orientation might be "rift" sawn, by definition, neither quartered nor flat sawn.)


EDIT:

Some examples of sissoo for use in guitars:
http://rctonewoods.com/RCT_Store/indian ... od-c-1_38/
http://www.vorreiterguitars.com/?page_id=804

thanks! very impressive!

[charles]

not common in the UK and Ireland.

It is in France: they make a LOT of barrels out of it.

I had a whole load of hassle trying to match as close as possible the tones.

That's what stain is for.

English, or "brown", oak is nice. I like the house, very nice.

My brother is an architect, as is my uncle. My brother is just finishing a $38 million estate in Sonoma California that the interior designer specified English walnut, rather than black or claro walnut. There is a LOT of walnut, thousands of board feet. She then bleached it to a uniform gray color.

Admittedly I was treating it (oil) to retain its fresh look, perhaps that was a factor in their advice? Still it was looking ok a year later:

It'll need to be oiled repeatedly, every couple of years, else it will fade to gray if its in the sun. Same for teak. An oil with a UV inhibitor will help.

this is a martial arts forum.

I've heard that rumour too.

[charles]

thanks! very impressive!

Any fine woodworker worth his or her salt knows this information.