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i have a stack of walnut in my barn, i bought a pin moisture meter, and was wondering where to ise it at, i tried end grain top and sides and it was all 8-10% i cut like an inch or 2 off the end of one board and it still measured 8-10% does this mean its ready to be used? i dont have any particular project right now, just curious. i cut it down and had it milled in December
Quote:
Originally Posted by cody michael
Cody, you will obtain the most accurate reading by taking the measurement in the center of the face of the board, with pin's that reach at least 40% to the center of the board. For a 3/4" - 1" thick board pins around 3/8" long are suitable. For an 8/4 board you will need 3/4" - 7/8" long insulated pins for the most accurate reading. I would suggest staying at least 10" or so away from the end of the board when taking a measurement.
You will obtain the LEAST accurate readings by taking the measurement from the end grain at the end of a board.
Wood dries from the outside in, and due to cellular structure it will lose or gain moisture very rapidly through the end grain. On the edge of a board, it is also losing moisture fairly rapidly, so that is also a less than ideal place to measure.
Readings will be skewed when taken in (or immediately adjacent to) a knot or portion thereof. The grain structure changes in and around knots and the moisture losing characteristics are frequently different versus the face of the board.
I have a Lignomat miniLigno pin meter i use to double check wood just before use, but given the need to shove pins in to the core it's hard not to think that they are not a whole lot of use until such time as the wood is cut open for use.
Do you have any idea Scott what's the best means of obtaining a moisture content reading from wood drying in a kiln? I've seen mention of using a meter, but realistically a hammer in pin seems likely to end up damaging the board just where you don't want it.
The (small/DIY) kiln operators i've spoken to just rely on control of the processing time delivering an acceptable number, but that seems potentially a little hit and miss?
I use a meter with the long pins and a hammer attachment for the kiln. I do it in the edge of the board on the center of the length. When I think that I am done, especially when I am not getting much more water out of the dehumidification unit, I can them check with a pinless meter on the face of a couple of sample boards before I unload the kiln. The good thing about a dehumidification kiln is that the unit can only dry the wood down to about 6%. So, when there is little to no more water coming out, then you are usually there, around 7 - 8%.
Ta Danny. A dehum kiln by holding the interior at a given % RH is presumably self limiting. (for anybody reading that's not familiar - the equilibrium moisture content of wood is determined by the %RH of the surrounding air, so that 8% EMC is equivalent to about 43% RH - the wood won't get any dryer than that if the kiln is held at 43% RH: http://www.wood-database.com/wood-ar...-and-moisture/ )
I'm researching the Logosol Sauno kiln which uses steaming followed by heating at 30 - 50 deg C while at a controlled rate venting off the moisture to dry the wood - the rate of drying it seems is controlled by the degree of opening of two air vents/the rate of intake of outside air. It doesn't directly control the % RH in the kiln, but does so indirectly and approximately by venting heated air containing moisture being removed from the wood and replacing it with outside air - so that ultimately it has the ability (say in winter conditions when the outside air is below 10 deg C and 70% RH plus as is common here) to pull the wood down to maybe 2 or 3% EMC if run at 50 deg C.
It seems like a meter might be useful to detect when the required dryness has been reached in this case.
Ian, between green and 30% MC, the industry standard MC% reading is to weigh sample boards and use the oven dry method to determine MC%. Below 30% you can use a moisture meter, or alternatively the oven dry method all the way down to final MC%.Quote:
Originally Posted by ian maybury
Hi Scott, I've done the weighing deal using a microwave to dry the wood, and have a miniLigno pin meter. Guess I was hoping there might be a more instant and convenient way of getting a meter reading from inside a kiln without cutting samples out of or poking holes deep into the wood with meter pins...
I just have a basic meter, I don't think I would want to stab the pins in that deep, could i drill a small 1/8 or so inch hole, then stick pins into wood?
The meter measures the electrical conductivity of the wood between the two pins, so the pins have to be in firm contact with the wood.