A few facts about wood: The Intro.

Understanding even a tiny bit about wood can make you a much better woodworker. So lets start with some basic safety advice:

Working with any timber is a potential health hazard:

The lumber you will likely use in wood working comes in three main categories:

  1. Natural Timbers
  2. Treated timbers
  3. Engineered timbers.

Natural Timber:

Describes any timber simply milled (cut) from a log or branch. However, before we go too far, let's look at some facts about natural wood.

 

Hard wood versus soft wood

Different species of trees produce different types of wood. While there is a lot of grey area between the two extremes, wood is usually grouped into two different categories. Slower growing (and often deciduous) trees often have more dense wood, and are called "hard woods". Faster growing trees (often ever-green trees) have less dense wood, so they're often called "soft woods". I'm sure that's a simplification, but for now that's enough.

A side note:

My university was genetically engineering Poplar trees (not "popular" as some people I know call it) to grow in even less time, but the wood was so poor they had a tendency to snap and fall down in only moderate wind. Being a public safety hazard, they were removed. Increasing the rate of tree growth, while attractive at first glance, is often false economy, so if you have a farm, and 50 years or so of life left in you, might I humbly suggest you plant rarer hardwood trees? They can often sell for over $50K each in todays money, and that'll get higher as demand and rarity increases. That's a pretty good retirement fund, and it's not quite as unpredictable as the stock market.

Don't get me wrong, I like soft woods, and they're strong enough for many tasks. I have no chance of breaking a 50mm x 100mm (roughly 2" x 4" in the old parlance) thick piece of pine, even if I jump on it... unless my weight is placed on a long cantilevered beam or something. My home-made work benches almost all use pine for the framework. House frames are often made of treated pine. It's not weak, it's just not as hard wearing as the harder woods.

Treated timber products:

Somewhere between natural timber, and engineered timber is the treated timber range. Treated timber is usually natural lumber (or ply wood, discussed below) that has been chemically treated to slow rotting and deter termites. You can see identify some treated pine products by a characteristic green-ish tinge. Some are intentionally dyed with unnatural colours to indicate that they're treated. However, it's not always easy to identify whether a piece of wood has been treated or not, especially if it has "greyed" with age.

To make matters more confusing, not all treatments are the same. Older treated products were treated with an arsenic solution (a potent poison) which has raised concerns about the safety to use it in places like playgrounds, and vegetable patches. Newer treated products, claim to be "safer" (note that safe-er is not the same as "completely safe") because they have used a different solution, by reducing the amount of arsenic (not removing it) and combining it with copper and chrome. (aka: "CCA" treatment). Copper deters fungus (and consequently most rot), Arsenic kills borers and termites, and apparently the Chrome bonds them together somehow. CCA treatments have been standardized and come in a variety of "strengths" from "H1" to "H6" (here in Australia). H1 refers to the "Hazard level". As you might imagine, H1 is the "safest" but also has the least wood protection. "H6" lasts the longest, but also has the greatest chemical risk.

Engineered Wood-like Materials:

While all wood must come from a tree at some point, your typical solid lumber isn't the only option around. Ply wood, particle board (a.k.a: "Chip board") and HDF/MDF (a.k.a: "High/Medium Density Fibreboard") are three of the most common products in this area. All of them involve some form of wood and glue, but they do it in decreasingly natural ways. The big advantage of engineered products is that you can build it to any size, dimension, and tweak them for different purposes without trying to grow the biggest tree conceivable. Most people won't be concerned about custom-made, ship-sized stuff, and just deal with the commercially available supplies. Let me outline the benefits and costs of each.

Plywood:

Plywood is the most natural of the big 3 engineered woods. Although that isn't saying much. You certainly won't see this wood being cut "as is" from a tree trunk. Instead, ply wood manufacturers take thin sheets of natural wood, then glue the sheets into stacks of odd numbered layers. You might be asking: "Why is it odd numbers of layers?"  The only answer I have been able to find is so that the grain on both sides goes in the same direction, giving it a more natural look. If you ask "why bother?" You see, each layer has in ply wood has the wood grain perpendicular to the layers above (and below it if it's not an end sheet). That way, the wood is strengthened and made more stable by doing so. (Note: wood expands/contracts based on the humidity of the air, but expand most across the grain as the fibres swell up, gluing each layer 90 degrees to the adjacent layers vastly reduces this expansion, so they're called "stable".) If each layer was oriented so the grain faced North-South, and the next layer East-West, (repeat as needed) and had an even number of sides, the two faces of that piece of plywood would have the grain going in perpendicular angles, making the wood look weird. It makes wood orientation yet another important thing us mere DIY'ers to forget to consider.

Plywood sheeting comes in thicknesses ranging from 2mm to 30mm (at least where I live). I've also seen up to 50mm in planks... usually structural treated pine, known by builders here as "LVL" or Laminated Veneer Lumber. Naturally, as the thickness increases and number of layers goes up, so does the weight, cost, and strength of the wood. Plywood also comes in various kinds. Some are hardwood, others are pure soft woods like pine. Some don't bother filling in the gaps between layers (called "voids") while others fill the gaps to make "void-less" options. Naturally, the void-less type is more expensive. Top grade ply also comes with consistent, knot-free hardwood finishes (top and bottom layers are blemish free) which might also be "marine grade" for exposure, and hardiness. Since I am an "in-lander" with no convenient coastal access, marine grade to me just means "pretty", allegedly more "resilient", and far more expensive.

Because plywood is made in numerous locations. There isn't always a consistent system to judge the rating of a piece of plywood. So do your research, and understand the ratings used in your area. If that's not an option, have a good look at any piece before purchasing, and consider the needs of what you're trying to do.

Particle Board/Chip Board:

Particle board is one of the most common components used in kitchen cabinetry (particularly the plastic coated/melamine coated stuff). It's basically a bunch of wood chips doused in glue, then squeezed under high pressure into boards of a particular dimension. If you've gotten into kitchen cabinetry, then you've probably seen the white melamine-coated variety at your local big box/hardware store. It has some interesting properties.

High and Medium Density Fibreboard (MDF):

HDF/MDF is another compressed wood product. Instead of using wood chips, it uses really fine sawdust and a ton of glue, compressed heavily to make sheets. MDF is a much more glue-determined as the wood particles are so much finer. You could honestly argue that it's a saw-dust reinforced glue product, rather than wood... strictly speaking.

MDF, like plywood comes in a variety of thicknesses, and often comes in large, easily available sheets.

A note about engineered and laminated wood...

While working with any wood will leave residues on your cutting blades/bits. The glue of engineered woods contribute to the accumulation of residue on your router bits, or saw blades, and "gum up the works" more quickly than with natural timbers. If you have laminated engineered woods,(like many kitchen benches) where the top is also covered with Melamine/Laminex veneers, these external coatings add even more chemicals "to the mix" then your blades may get "gummed up" after surprisingly few cuts. I've seen people throw away bits and blades because they simply "don't cut well anymore".. Have a look at those teeth edges. Is every tooth on your circular saw blade intact, but it's somewhat sticky, or grimy? Does it take forever to cut? Try taking the blade out of your device and rubbing/soaking/cleaning your blades with some concentrated washing detergent (some even use dish washing detergent). Have a look at the video below, I've skipped the Festool advertisement at the beginning for you, and it's only 85 seconds long. If it saves you from buying a $30 (or more) blade, using items already found in your home, then I consider that time well spent.

 

Wow, that was a lot of info in a page. Ok that's enough for now, I hope this has been helpful. Have fun!

Ham.