Replies

1. 
   PlaneWood | Oct 08, 2003 10:18pm | #1

   Well, you don't wanna use green lumber! 

   Some species, like black walnut, will air dry fine and can be used to make fabulous furniture.

   But, all wood regardless of how it is initially dried, will expand and contract with changes in humidity.  There will be different rates of expansion across the grain (radial) than with the grain (tangential).  There are charts that will give the expansion coefficients for all species.  Some species can change as much as 1/2" across a 4' width.  And, there is nothing you can do that will stop it from moving.

   So, table tops must be allowed to float.  That is, the top is fastened to the skirts in such a way that it can expand and contract across it's width.   There are various ways to do this.

   If your shop humidity is higher than that in your house then the wood will shrink as it drys out in the house.   The converse is true if shop humidity is lower.  I've seen beautiful table tops that split down the center cause the float was not done or not done well.  One was a 20' long table in a church that happened to be placed right under an heating/AC outlet. 

   Hope that helps!

   PlaneWood by Mike_in_Katy (maker of fine sawdust!)
   PlaneWood

1. 
   sixmanfan | Oct 08, 2003 10:41pm | #3

   Can you tell me where I might find the techniques to attatch the top to let it float. Like I said I am a rookie and the more I research this the more I wonder if I can do it properly! Also my local lumber yards do not keep kiln dried lumber am I better off ordering some and getting it shipped to me or can I use the lumber straight from the lumberyard?

   Thank you very much for taking the time to tutor me.

   Gary

1. 
   rod | Oct 09, 2003 03:47am | #4

   Sixmanfan,  Garrett Hack had an article on this topic in FWW, I don't remember the issue.  It is reprinted in the Taunton Book,  "Practical Design, solutions and strategies".  There is a lot of other useful stuff in this volume.

   Rod

2. 
   jonsherryl | Oct 08, 2003 10:30pm | #2

   Sixman, kiln dried stock will be more stable in the humidity ranges the wood will be exposed to as a piece of furniture in a typical, centrally heated house. Especially in a temperate climate zone with cold winters. In other words, Kiln dried stock is less likely to fail (check or distort) as the wood's moisture content experiences levels BELOW it's MC at the time it was removed from the kiln (below the 8% to 10% range.) Actually the wood, whether kiln dried or air dried, will seek what is called its Equilibrium Moisture Content...which in most regions of the Midwest averages around 12%. It's just that KD stock performs better at the drier end of the spectrum, which is more important in most, cold climate, interior applications.

   Two other factors must be taken into consideration when deciding which way to go: 1.) the species of wood you choose and, 2.) how important its shinkage properties are likely to become in how you are using it. Some woods, like maple, beech, elm and oak aren't as naturally stable as are genuine mahogany, cherry or walnut...and, unfortunately, wide edge-glued panels (like a table top) are a risky proposition with respect to what can happen if they distort.

   Also, just what you can get away with depends a lot on the joinery you choose. If your design allows the wood to float, you can accommodate some shrinkage and distortion...But for a beginner, making a table for use in a centrally heated home, my recommendation would be to opt for kiln dried stock. You'll develop a sense of how far you can push air dried stock of the various species as your skills progress...but, if I were you, I'd save those lessons for simpler and smaller projects, at least for the time being.