This postings’ objective is not to get into the “weeds” of the engineering but rather, to help the new(er) woodworker understand and decipher some of the erroneous and misleading hype often thrown about when talking about wood and its hardness. That said, this will likely be longer than I envision for a normal posting.
I will only discuss two basic considerations in wood engineering, Hardness and the deflection resistance (bending). Another consideration is impact resistance, there are others forces engineers look at, but for this discussion, I kept it to just the basics two.
As we know, wood is harvested from something live. Because of this, there are many variables to each piece cut. Along the road of the woodworking, each piece you cut can and will provide you insights on how to improve your ability to know what to look for when buying wood and understand how to “piece it together” so it looks the best as a finished product.
Identifying wood type and matching need and appearance to a project:
Picking the end look is often how we all start. That said, the next thing to think about is how it will go together to be strong enough for the intended use. Weight is a consideration that come in to play as well.
Understanding the misnomer of wood hardness for strength is often a common statement with woodworkers. Strength of wood is more than surface hardness, which is the often touted “Janka” rating.
For those who are unfamiliar with the Janka system- The Janka hardness test measures how many sq ft lbs pressure is required to embed a .444-inch steel ball (roughly 11mm) to half its diameter in wood. The purpose of this test is to measure wood species ability to withstand denting and wear. It is also a good indicator of how hard or easy a species of wood is to saw or nail. E.G. Northern Red Oak, has a Janka hardness of about 1290. Brazilian Jatoba, has a rating of about 2350. If desired, you can look up more on Janka on the internet.
But with wood, that is only one consideration. Modulus of Elasticity (MOE) is another. Simply put, how much bending stress (deflection) can a piece of wood take before it fails. Failure can be described as warping due to the stress or cracking or breaking. All are failures if that is not what you want.
This is what engineers look at when a building is being constructed out of wood. As a wood worker, this is something we need to have a cursory understanding of. So, when we build anything, we are also considering how to reinforce something in the build to assure it does not fail.
An old adage one of my engineering instructors told me –“ anyone can make something strong and heavy, but the skill is making it strong, light and efficient”.
Back to wood. The things I look for when matching wood is grain and its direction. Be a keen observer of wood grain and really look at how the wood grain moves through the board. This is really important., epecially if the wood is being sold at a cheap price. Things to avoid would be when wood grain wanes (starts moving in a differing angles suddenly), of course, knots and “Y” forks, and other defects like ring or heart check, cat or dog facing (where the Wye starts but then is reabsorbed in the early growth of the tree), pest holes or pith or punk…….. Unless you want that. Sometime this can be a cool feature(s).
Of these, the subtle wane and things like that are the real scourge - often discovered only when you begin to plane. I run into this a lot with certain woods, Iroko, African Teak, some Mahoganies and some other Exotics. The thing is, when you look at it 1st glance, you really cannot see it. But, upon careful inspection you will see some signs, for me? about 80% the time I catch it. Great odds if it is a poker game, but when it happens after hours of work……… yeah, not so fun. Wane is a real potential structural failure point, particularly when it is near a joint. Keep that in mind.
THIS – is where understanding your tools and having them sharp will help.
Enough rambling- this is a big subject and better understanding and knowledge of this benefits all. Hope this helps enhance your discretion when acquiring materials and when thinking about how something goes together and how strong it will be when completed.
I will only discuss two basic considerations in wood engineering, Hardness and the deflection resistance (bending). Another consideration is impact resistance, there are others forces engineers look at, but for this discussion, I kept it to just the basics two.
As we know, wood is harvested from something live. Because of this, there are many variables to each piece cut. Along the road of the woodworking, each piece you cut can and will provide you insights on how to improve your ability to know what to look for when buying wood and understand how to “piece it together” so it looks the best as a finished product.
Identifying wood type and matching need and appearance to a project:
Picking the end look is often how we all start. That said, the next thing to think about is how it will go together to be strong enough for the intended use. Weight is a consideration that come in to play as well.
Understanding the misnomer of wood hardness for strength is often a common statement with woodworkers. Strength of wood is more than surface hardness, which is the often touted “Janka” rating.
For those who are unfamiliar with the Janka system- The Janka hardness test measures how many sq ft lbs pressure is required to embed a .444-inch steel ball (roughly 11mm) to half its diameter in wood. The purpose of this test is to measure wood species ability to withstand denting and wear. It is also a good indicator of how hard or easy a species of wood is to saw or nail. E.G. Northern Red Oak, has a Janka hardness of about 1290. Brazilian Jatoba, has a rating of about 2350. If desired, you can look up more on Janka on the internet.
But with wood, that is only one consideration. Modulus of Elasticity (MOE) is another. Simply put, how much bending stress (deflection) can a piece of wood take before it fails. Failure can be described as warping due to the stress or cracking or breaking. All are failures if that is not what you want.
This is what engineers look at when a building is being constructed out of wood. As a wood worker, this is something we need to have a cursory understanding of. So, when we build anything, we are also considering how to reinforce something in the build to assure it does not fail.
An old adage one of my engineering instructors told me –“ anyone can make something strong and heavy, but the skill is making it strong, light and efficient”.
Back to wood. The things I look for when matching wood is grain and its direction. Be a keen observer of wood grain and really look at how the wood grain moves through the board. This is really important., epecially if the wood is being sold at a cheap price. Things to avoid would be when wood grain wanes (starts moving in a differing angles suddenly), of course, knots and “Y” forks, and other defects like ring or heart check, cat or dog facing (where the Wye starts but then is reabsorbed in the early growth of the tree), pest holes or pith or punk…….. Unless you want that. Sometime this can be a cool feature(s).
Of these, the subtle wane and things like that are the real scourge - often discovered only when you begin to plane. I run into this a lot with certain woods, Iroko, African Teak, some Mahoganies and some other Exotics. The thing is, when you look at it 1st glance, you really cannot see it. But, upon careful inspection you will see some signs, for me? about 80% the time I catch it. Great odds if it is a poker game, but when it happens after hours of work……… yeah, not so fun. Wane is a real potential structural failure point, particularly when it is near a joint. Keep that in mind.
THIS – is where understanding your tools and having them sharp will help.
Enough rambling- this is a big subject and better understanding and knowledge of this benefits all. Hope this helps enhance your discretion when acquiring materials and when thinking about how something goes together and how strong it will be when completed.
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