Replies

1. 
   jackplane | Sep 11, 2006 08:08pm | #1

   The ideal moisture content is between 6-9%, for all woods, and does not vary between species. But 11-12% is not too bad, depending upon what is being built, and the construction involved. (6-9% , from Wood and Wood Products magazine).

    

1. 
   daryl | Sep 11, 2006 08:32pm | #2

   I think the ideal moisture content is the one that matches where the piece will go. Another good way to make sure it will be OK is to see what your workshop is. An easy way is to put a meter on your workbench, since it has generally sat there for a long time. Mine hovers in the 9-10% range (hard maple).

1. 
   jackplane | Sep 11, 2006 10:13pm | #3

   It's true that one must account for where the piece will go. If you ship to arizona for example, the mc needs to be far lower than if the piece is sent to the Northeast, relative to where it's made. 

2. 
   JohnWW | Sep 12, 2006 03:49am | #4

   To build furniture, the moisture content of the wood should be at equilibrium with the relative humidity in your shop, having it at any other level is nearly impossible to maintain anyway once the wood is brought inside to work with it.  The best way to achieve equilibrium is to just sticker it in your shop for a few weeks. 

   You should presume that the finished furniture could be exposed to some fairly extreme conditions over its hopefully long life, and the design should accomodate a 12% change in moisture content, from around 4% to 16%, to be safe.

   John White, Shop Manager, Fine Woodworking Magazine

1. 
   quietude | Sep 12, 2006 08:47am | #5

   Thank you for all the information. It has been most helpful.
   luke

2. 
   KingwoodSteve | Sep 15, 2006 04:53pm | #6

   John,

    Please forgive my ignorance but I am at the beginning end of understanding how much humidity affects wood, and being from the Houston area, I guess it’s something I need to learn early.

    You say that a design should accommodate a 12% change in moisture content. Could you expand a little on that statement? I understand that table tops, panels and so forth need to allow for expansion but I took your statement to mean all aspects of the design. Does this include joint work too? DT’s and M&T joints are supposed to be snug, so how will this affect them?

   Thanks,

   Steve

1. 
   JohnWW | Sep 15, 2006 05:29pm | #7

   Steve,

   With dovetails, both halves of the joint have the grain running in the same direction, so no stress is built up.  The thickness of the stock will change enough that in some cases the tails and pins might be a bit proud or sunken.

   Mortise and tenon, up to perhaps 4" wide, typically doesn't have a problem, but after that you need to start to plan on the tenon part shrinking enough that it might crack if too solidly attached.  You definitely need to plan out very large M&T designs like bed head boards tenoned into the posts.

   Where you are located doesn't really matter, what counts is where the furniture ends up, and, except for built in furniture, the only safe approach is to plan on the worst, which is why I try to design for a very large moisture content change.  

   An 8% to 10% swing is quite conceivable, moving a piece from Maine to Florida, for instance, so I use 12% to be safe.  Except for designing in a bit more room for movement, there isn't any difference in planning for a large swing over a smaller one, so I play it safe.  

   Also it isn't just expansion and contraction that needs to be considered, even perfectly dried, fitted, and finished flatsawn boards will cup with gains and losses in moisture and this needs to be planned on also.  I could, and very well may, write a book on the subject, there is a lot to consider.

   John White 

1. 
   KingwoodSteve | Sep 15, 2006 07:13pm | #8

   Thanks John,

    keep us posted on the book. I, for one, will be in line to buy it.

    

   Steve

1. 
   JohnWW | Sep 15, 2006 09:03pm | #9

   You'll get the first copy.

   John W.