Monday, November 30, 2009

DIY WoodWorking - How to Determine Warp

Warping is one of the home DIY wood craftsman's biggest headaches. After you've spent considerable time, painstaking effort and care in creating a beautiful hand-crafted piece of furniture - it is a disappointment to have it later warp and shrink. Here are some tips for DIY Woodworking - how to determine warp.

Warping and shrinking of wood can be held to a minimum if the wood is properly conditioned and attention paid to moisture content when working with wood.

How Wood Warps
Wood warps and shrinks in relation and direction of the tree's annual rings. Shrinkage turns out to be twice as great when the direction is parallel to the rings as when it is across them. Edge-grain wood (quarter-sawn) shrinks the least because the heaviest shrinkage tends to take place across the narrow dimension of the board. In a quarter-sawn board, the end grain angles between 45 and 90 degrees, across the edge of the board, with the grain running up and down.

Flat-cut boards have the greatest warp and shrinkage potential because they tend to cup away from the heart side of the wood. When facing the cut edge of the flat-cut board the grain runs in half circles and the board tends to cup away from the heart of the wood or "down."

How To Detect Warp
One of the easiest ways to test warp is to take your board and put one end on the floor and sight along the other end down the board. Turn the board over to sight it from both sides. Any end warp or twisting can be easily seen using this method.

Any irregularity caused by warp should be removed before you use the wood. A board that is warped will continue to twist as it dries out no matter how it is used.

Conditioning Wood
Conditioning wood means seasoning the wood to the proper moisture content (MC) to correspond to the humidity of the wood (or project's) permanent location. A general rule of thumb is to have a MC of between 9-12%. A variation of about 3% is acceptable.

If you live in an area that has a humidity factor of about 40% indoors, then the moisture content for your wood furniture should be around 8%. So if the wood you are using for your project has a MC of 8% to begin with, you won't experience massive expansion and contraction through the seasons.

Easy Method to Check for Moisture Content
Saw a small piece of wood from the wood to be used in your project. Weigh it with a small kitchen scale that reads grams or grains. Now place the sample of wood in the kitchen oven at about 220 degrees F. and weigh it every 20 minutes until it stops losing weight. This will take about 1.5 hours. Take the difference of the beginning weight and the ending weight and divide that by the finish weight and that should give you your moisture content.

As an example, your wood sample weighs 155 units to start, 136 at finish with a net change of 19 units. Divide 19 unites by the 136 and you will have a finished moisture content of 14%. Though your sample is bone dry, it won't stay that way. Within 3 or 4 hours it will regain approximately half of the lost moisture and size and in a few weeks be back to normal.

Wood is truly never seasoned. Even wood that is a 100 years old will absorb 16% to 18% moisture if stored outdoors. If you remember to store your wood in a location where the humidity is about the same as where the finished product is used - your wood should be in a good shape.

Autor: Laurie Brenner

I know how it feels to build something only to have the wood warp on you. One header we put in our house that served as the portal from the great room to the kitchen had to be replaced twice. The header, including the posts, kept warping and twisting on us. It can be frustrating until you learn how to determine warp and pick the right pieces of wood for your projects.

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Added: November 30, 2009