Day 2 continued

How Dry is Dry

Water occurs in wood in two places, First, theirs the free water that fills the inside of the wood cells. That's like water in a bucket. Second, water also infiltrates the cell walls. That's called bound water. Imagine squeezing a piece of cotton Cheeses cloth until all the free water is drained away. The cloth though, remains damp because the material continues to contain moisture-the bound water.

When wood contains bound water its is said to be in its fiber saturation point. And the bound water can be eliminated completely only by drying it. Somewhere with no relative humidity, as in an air-tight oven.

Wood likes water, wood rates as a hygroscopic substance. Thai is it has ans affinity for water and readily absorbs it as a liquid and vapor. This ability directly deepens on the humidity of the surrounding atmosphere. therefore the amount of moisture is wood changes as the humidity changes.

The term Kiln-Dried means that wood moisture was removed in a chamber where air circulation, humidity and temperature were controlled.

Bow, Cup, Twist Crook

What Shrinkage does to wood

Woodworkers call the change in shape of a piece of wood warp. And it takes several common forms, all of which distort the wood.
Bow, as its name implies, describes the lengthwise curvature for board-end to end along its face. Twist, means that all of a boards corners won't lie equally flat. Crook, all the curvature runs end to end alone its edge. Cup, is when a board no longer flat from edge to edge. Cup always occurs in the opposite direction of a flatsawn board's annual growth rings. Although not a distortion like any form of warp, checking refers to the Small splits along the grain. You'll most often see checks in the ends of boards but they can occur on surfaces too. This is due to the fact that wood dries 10 times faster along it length compared to drying across the width. One of the things we will learn in our class project is to project wood movement and design and build with this in mind.

Defects in Wood

Knots are limbs separated from the tree trunk during tree growth.

Wane is bark on the edge of a board.

Pitch Pocket is an opening in a board containing pitch.

Splits is the tearing apart of wood cells due to improper storage or handling.

Checks are the lengthwise separation of wood due to shrinkage.

Measuring Wood

The standard method of measuring hardwood is given in board feet. We will be calculating the board feet we will need for class project. Including any projected waste as part of our calculations.

One board foot is described as 12 inches by 12 inches by 1 inch thick or 144 cubic inches. This is calculated by multiplying length x width x thickness.. examples of a board foot are 3x4x12 and 2x4x18 and also 1x6x24. All these measurements give 144 cubic inches of lumber. We will be using a bill of materials for the workshop to determine how much wood we will need for each project.

Grading Wood

FAS (first and Seconds) This is the best grade, boards are 6" and wider and 8' and longer. Almost clear and yeidls 8 32/3 percent clear face cuttings 4" or wider by 5' or longer and 3" or wider and 7' or longer.

Selects, The boards 4" and wider, 6' and longer. one side is FAS the is no 1 common. Yiedls 832/3 percent clear face cuttings.
No 1 common, Boards are 3" and wider, 4' and longer and yields 66 2/3 percent clear face cuttings 4" or wider by 2' or longer.

Urban Forestry in California

In 1989 the legislature passed a bill to reduce solid waste by 50% by the year 2000. One unique outcome put forward by Eric Oldar of the California Dept of Forestry was to promote the value of the lumber cut from trees in Urban locations and to promote organizations to harvest urban lumber as an economic venture and to reduce solid waste.

Palomar College Participates in Urban Forestry with a Wood=Miser portable ban saw and Kiln for drying the lumber. Student participation in the Urban Forest Program is part of the class requirements and more will be covered on this subject in future blogs.