Wood

Part 2 - Where Wood Cuts Come From, and Where to Use Them

Details
Hits: 15338

Even though wood has been around as a building product for millions of years, it remains one of the most complex building products due to it inherent properties. THe more you learn about wood the more there is know, and when you are a woodworker, understanding your building medium will put you miles ahead in saved time, costs and satisfaction with your projects. Have you ever wondered why some of your woodworking projects buckle, bend or crack? Well, the answer may be the way it was built, or it could have been the "cut" of wood you used. This article will attempt to help explain some of the charcteristics of wood to help you make some better choices in selectinb your building materials and assembling your products. Click below to read more ...

If you are starting off by reading this article, stop and go back and read Part 1 of this article first, it will only take a few minutes and it will make this article much easier to understand and apply.

When we look at the three primary cuts of boards, Flat, Rift and Quarter, it is evident that the growth rings run at different angles. This is critical to understanding how wood behaves. You should first of all know that all wood is constantly moving. The reason it is constantly moving is that wood is always either absorbing or dissipating moisture. Where ever wood is stabilizes itself to the conditions around it, if the air is moist, wood absorbs moisture, if the air is dry the wood sheds moisture until it is stable with its environment.

Another thing to know about wood is that during it expansion and contractions it only moves is certain directions. Wood will not expand in the direction of the grain. To explain this a bit more, it you purchase a simple 8 foot 2" x 4" board, and put it in either a moist or dry environment, the board will not get any longer or shorter, it will always remain (with in mico meters) of its original 8 foot length.

The same 2' x 4" board in placed in moist or dry atmospheres WILL change width and depth. This is because wood absorbs water within it growth ring directions. Predicting how much a board will expand across its width and depth is very difficult because it depends on th type of wood and the cut of the board. For example a quarter-sawn board will expand more across it face than will rift sawn, and a flat-sawn will expand very minimally across its face, but it will expand a lot across its depth.

It is these same reasons, those of expansion and contraction that make Rift-sawn boards the worst culprits for turning out "propellers" (boards that are often twisted beyond use and end up as firewood).

So ... what are the pros and cons of each type of board and where should they be used?
Flat-Sawn boards are often considered the most beautiful of the cuts with the grain displaying the beautiful "cathedrals" up the grain of the board. These boards are ideal for large visual areas like kitchen cabinet doors, drawer fronts or the sides of dressers or other large similar projects. These boards are quite stable dimensionally, across their width. Where you may not want to use them are as treads when building a stair case as these boards will flex and bend under pressure, they would be great for risers on steps with the visual appeal and their strength in that direction. For treads on a stair rift would be better but quarter-sawn would be best for the treads. Flat sawn is also a poor choice for decking or flooring. Besides always tending produce slivers, they will also tend to warp or cup due to the expansion across the depth of the boards.























Rift-sawn boards are probably the least desirable of all the cuts. This is because these cuts can vary quite a bit depending on where in the log they are cut. They also tend to "move" in two directions with makes them poor choices for flooring, table tops and decking. Rift cut is often left for building materials like 2x4, 2x6s, 4x4 and so on. This does not mean that good quality hardwoods are not available in rift-sawn cuts, only that it is often not the ideal cut.

Quarter-sawn is considered by most the ideal cut, and in some ways it is. Quarter-sawn is not as attractive as flat-sawn and is really designed for different building area. Quarter-sawn wood is ideal of table and chair legs, spindles and other long straight pieces. If you are looking for real wooden flooring you will want to lay down quarter sawn (also called edge grain) flooring. It lasts for ever, is quite stable, very strong and does not easily produce slivers.

There is a lot more to learn about wood but this will at least give you a sampling of how woods react and where to use them for more effective and pleasurable projects.

 copyright Colin Knecht
woodworkweb.com

 

PLYWOOD - The Good, the Bad the Alternative

Details
Hits: 34831

I spend good money buying what I am assured is "good quality plywood ", so why, when I get it home, does it make me want to turn it into firewood?. That was the hard hitting comment from an associate of mine recently. He's not the only one who is disappointed in the quality of plywood ... thousands more just like him have the same comments, I hear it ALL THE TIME!!.

So, lets talk about plywood and why it is the way it is, how can we best use it and what are some alternatives. First of all there are two kinds of plywood, "sliced" and "rotary". These terms are used when talking about the face of the plywood. So if you were to purchase a three-quarter inch 4x8 sheet of "Oak Plywood", you would have the choice of purchasing either "sliced" or "rotary". So ... what's the difference other than price you ask ... whew, a LOT .......

Of the two kinds of plywoods "sliced" is the most expensive and the most attractive as it simulates boards of wood. Rotary plywood manufacture costs less than the sliced method and it looks more like "plywood", but here are the two methods for actually making plywood.



"Sliced" plywood is just as it says, slices of wood are sheared off with a giant knife, just like slicing cheese. These are then assembled on the face of the plywood core where they are glued and then sanded to make the finished sheet.



"Rotary" plywood on the other hand is made quite differently. A select log is mounted on what is essentially just a huge lathe. When the tree is spinning a high rate, a large blade digs into the tree deeper and deeper and at the same time a long flat vaneer is unfurreled off the blade. It is this veneer that is then glued to the plywood core, then sanded to make the finished sheet.

Now ... lets talk about the "core" for a minute. Most hardwood sheets of plywood use less expensive softwood cores on which to build the hardwood face of the plywood. Much of the problems with plywood are a result of these cores, and here's why. Some of the cores are not well made, they may have "voids" in them, or the quality of the wood they are made from may just be of poor quality. To compound these quality issues, some of the wood that is used to create these cores is dryer that other portions. Some of these veneer sheets within the plywood expand or contract depending on how wet they were when they were used to make the "cores", and what the atmospheric conditions are where they are stored.

When you purchase plywood that says its 3/4". According to the Plywood Manufactures Codes, it does not mean the plywood is exactly 3/4" ... it means the plywood will not EXEED 3/4", which means it is always somewhat less than the 3/4" ... sometimes by 1/16th" (or more).

This means that if you are sizing a project or cutting dados, rebates etc. It is more likely than not that the wood is going to be lose in these because if you followed the instructions of the dado blade and made it exactly 3/4" ... it will be too big for the plywood. Also, if your project has one 3/4" piece on either side and those sheets are actually 1/16th shy, your entire project will be 1/8th narrower ... see the problems this can create!!! AND, WHAT'S WORSE ... if you purchase two or three sheets of plywood, there is an excellent chance NONE of them will be exactly the same depth, in fact, there is a good chance none of the sheets will be consistently the same depth along each edge.

Like all other problems that woodworkers encounter, there are solutions.

Solution #1 - don't use plywood - I say this a bit "tongue-in-cheek" because we all know we MUST use plywood for many projects, but now we can be a bit more selective.

Solution #2 - re-manufacture the width of each edge of plywood you will use. Now I know this sounds tedious, but it's not that bad, and considering all the time you save by using plywood, you can afford to use up a bit of that time making it perfect. The re-sizing of an edge can take a few different methods, such as running all your edges vertically through your table saw to have every edge exactly the same.

Solution #3 - Use the Medium Density Fibre (MDF) and similar versions of hardwood sheets. Some of these come with hardwood vaneers laminated to their face sides, others are plain. Generally speaking, these sheets are flat ANS evenly thick because of their method of manufacture. Of course they have other challenges, like heavy weight, poor substance for using screws with and some will absorb water either from the air, or from "puddling", which makes them swell and become weak.

Well, that's the story of plywood ... love it or hate it, it remains a great product for many applications, but not necessarily the only product. Like anything you do in woodworking selecting materials is half the battle and knowing what to look for and what application you are working on will go a long way in helping you select the right materials.

Copyright - Colin Knecht
wooworkweb.com