Friday, August 15, 2014

Wood Panels and Humidity

Coping with wood movement

All wood workers need to be aware of wood movement when building furniture projects. Failure to consider this important factor can cause wood panels to crack or split.

My high school biology teacher compared the structure of a piece of wood with a bundle of straws. The straws represent the cells and capillaries of the wood. When a tree is growing water and food are transferred up through the cells and are carried throughout the tree.

Once a tree is fell the free water in the wood is lost rather quickly but the bound water trapped in the straw like cell is slower to dissipate. As the level of bound water is reduced these straw like cells get narrower in diameter but maintain their length. This is the fundamental reason that wood expands and contracts across its width but has almost no expansion length wise.

When working with wood it is very important to allow the wood to expand and contract with changes in humidity. As humidity rises the straw like cells expand in diameter with the opposite effect occurring as the relative humidity falls.

Ways to accommodate expansion

Lets use a cutting board for the first example. A solid wood cutting board with a bread board edge secured with a tongue and groove joint. One edge has the bread board edge secured on both ends with a dowel through the tongue The other bread board edge is secured with the same tongue and groove joint but this end only has a dowel in the center of the piece.

The end secured with two dowels will develop a crack in the main panel. Since the length of the edge piece doesn't change having it fixed across the width of the main panel from expanding.

Alternatively, the opposite end of the cutting board is only fixed in the center. The main panel is free to expand and contract towards the ends. The only visual difference would be that the ends of the edge piece are no longer flush with the edge of the main panel.

The second example uses a large glued up panel such as a table top. If the table top was fixed to the rails across the width of the panel the rise and fall of humidity would undoudtable cause the panel to split.

The best method to overcome this is use wooden clip to attach the two pieces. A 1/4" x 1/4" dado milled on the inside upper edge of the rails. This accepts a wooden clip that fits into the dado and is then secures to the underside of the table top. This will security hold the top hold the top onto the rails without restricting the expansion and contraction of the large panel. Without this the table top would slowly start to open up.

In general anytime you are fixing one piece of stock across a large glued up panel measures need to be taken to allow the panel to move. Remember that it will expand across its width but not its length. Using one of the two methods mentioned above you will be able to prevent your glued up panels from splitting.

Thursday, August 14, 2014

From Toss Out to Sensational Keeper - Lamp Re-Make

When the old lamp from my children's room was turning decidedly "trash-worthy", a grand idea formed and kept me from tossing it out. Originally, it had been such a darling lamp - it had magically transformed the room into spinning stars and moons at bedtime. My boys were enthralled with it!

Well, as the boys grew, so did their access advantage to the lamp. The inner spinning mylar cylinder with the moon and star designs turned into a mangled, crumpled, ripped up piece of multi-colored plastic. There was nothing salvageable there. What was left, however, was a perfectly functional light and a plain wooden frame that held four blank canvas panels. Since I couldn't possibly throw a working lamp away no matter how plain and ugly it was - I had to jazz it up!

Here's how I did it:

1. I "washed" the canvas panels with a "butter cream" colored bottled acrylic diluted with water using a 2" brush. To create a weave pattern, I first made vertical strokes on all four panels then went back and did horizontal strokes.

2. I carefully painted the wooden frame with a dark brown bottled acrylic using a small artists' brush. (if you're not confident with your painting skill - use painters tape on the canvas panels to avoid getting the brown paint on them)

3. As soon as the frame and panels were dry, I planned my stencil placement and then taped the stencil in place using masking tape.

4. I chose a Chocolate color in a Delta Stencil Cream. After removing all excess paint from my stencil brush on a paper towel, I stenciled the design on all four panels using a circular motion. I used a design from our Plaster Petite's Line, set #1.

5. For the finishing touch - I used four pretty finials that I attached to the four corners of the frame with white glue. If you don't happen to have any finials hanging around your house - check out your local home store. You'll find great finials in the window treatment aisle OR try a really awesome decorative drawer pull for the top! Get creative! Elegant or funky! Just don't move the lamp until the glue is completely dry or you will have four falling off finials!