Replies

1. 
   hammer1 | Mar 15, 2008 09:47pm | #1

   If you buy KD cabinet grade lumber, it should be close to 8% moisture content. If it's 12% you may want to find a different supplier. The moisture content will increase if the lumber is stored in a place that has high humidity. One of the best ways to keep it stable is to sticker it in storage, this way air can circulate around each piece. After milling, you should also sticker it for the same reason. In the milling process, if you take more off one side than the other, it's likely to warp. If you rip narrow pieces from wide boards or you resaw thicker stock in half, the probability of warping increases.

   Boards seem to have an integrity once the have been sawn from the log and dryed. When you cut them in the ways I've described, you change the dynamics of this integrity. Depending on where the board was cut from the log and the nature of the grain, some are more prone to moving around. With experience, you have a good idea which ones may be trouble and what operations may contribute to those problems. It's still not 100% controllable in every case.

   Woodworkers use all kinds of tricks to help alieviate the tendency to warp. Some will partially mill and let the stock rest for a time. Blowing a fan on the pile in adverse conditions can help. I mill to thickness, keep it stickered and try not to let it sit around. If the rough board is warped and twisted to begin with, chances are, that it will want to move in that way later on. It's already shown it's character. Many of us like knarly wild grain in some work. Cautious milling, flatening on a jointer before planing, proper storage, air circulation and avoiding interupting the integrity are your best hopes.

   Beat it to fit / Paint it to match

1. 
   Nollie | Mar 15, 2008 10:04pm | #2

   Hi,

   Thanks for the advice. It would be very helpfull. Down south in Africa i have contacted 4 suppliers of lumber and all of them specify 12% moisture. They say that they do not supply lumber with a lower moisture than 12%.

   It seems to me that i have to make another plan. Mill the wood and stack them in the way you sugested and let it settle out for some time

   Thanks

1. 
   SgianDubh | Mar 15, 2008 10:56pm | #4

   hammer has given you broadly useful advice. There is another option and that is to pay someone to kiln the wood to 7% or 8% MC if that is the requisite MC for the wood you are working with. You could also build your own solar kiln quite cheaply and put the wood through a final conditioning cycle. I imagine the climate is hot enough, dry enough and sunny enough to run a solar kiln cheaply and efficiently.

   I suspect you work in a dry workshop, one where the relative humidity (RH) is somewhere south of 50% RH which results in wood reaching 9% MC and lower. Perhaps your problems occur on a seasonal basis if your workshop has no climate control and the warping occurs in the dry season. I'm not sure of the seasonal cycle in South Africa, and obviously I have no idea what kind of workshop and climate control you have within it.

   However, I have to say that it isn't always 'right' to build furniture or wooden items out of timber that is at 8% MC. It's right for some things, and too dry for others. You will have to provide more detailed information about your workshop conditions and the like before I could provide more specific advice. Slainte. Richard Jones Furniture

2. 
   hammer1 | Mar 17, 2008 02:26pm | #5

   12% moisture content would be a big problem in my climate. We heat six to seven months a year, joints would open up due to shrinkage. A simple electric fan is an easy way to keep air moving. I run a couple in my shop around the clock in humid conditions. They help with rust on tools as well. Wood has a mind of it's own, though. Attempts at perfection are just that, and often frustrating. Even at 7% content, uneven milling will cause problems. When cutting up larger stock, you never know how it will react. I try to allow for corrections when faced with this situation but I still get zinged from time to time.Beat it to fit / Paint it to match

1. 
   Nollie | Mar 17, 2008 08:12pm | #6

   Hi,

   You gave me some good advise guys-thanks.  The wood that is giving me the most problems is what we call Rooswood(Guibortia Coleosperma). We get the wood from Zambia And Angola. I am attaching a photo of piece that i made. A dense wood that finishes very nicely- 800 kg per m3. I borrowed a moisture meter from a friend and tested the moisture on all the lumber that that i did not mill. The MC varied from 14% to 17%.The supplier sell it for 12%.  That for our kiln drying standards!!

   I searched the web and came across a web site called Wood web. Very good information on solar kiln drying. They also give some plans on different kiln designs and operating instructions.

   I will have to build a solar drier to condition the wood to the final MC. Thanks for this advice from Great Britten.  The wood that we get from the USA and Europe is also at 12%MC.

   African Greetings  

   
1. 
   JohnWW | Mar 17, 2008 11:14pm | #7

   The MC of the wood at the moment it came out of the kiln may very well have been 12%. In a humid environment it would immediately start reabsorbing moisture from the air unless it was wrapped in an airtight tarp. Unless that was done, and you have a shop with a humidity controlled environment with a low RH, the wood will always gain or lose moisture to reach a balance with the moisture in the air around it. If you are expecting kiln dried wood to stay a a fixed MC you are always going to be disappointed.John White

2. 
   SgianDubh | Mar 15, 2008 10:40pm | #3

   "If you buy KD cabinet grade lumber, it should be close to 8% moisture content."

   That's true in North America hammer. It's not the case in other parts of the world. Here in Europe, and evidently in South Africa, kiln drying standards are different.

   In the UK for example standard practice is to dry to between 10% and 12% MC. However, there are moves afoot Europe-wide to change the standard to a lower final MC of, I think, 8%. This is close to the North American norm and it reflects the changes in the climate control now available in European habitable buildings, and the typical RH numbers these buildings exhibit throughout the yearly cycle. Slainte.Richard Jones Furniture