Air Drying - Woodworking Talk - Woodworkers Forum
 
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post #1 of 12 Old 03-26-2011, 05:12 PM Thread Starter
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Air Drying

Air-drying logs and parts of logs involves some science and luck. You can find tomes of information about drying lumber on the internet, written magazine articles and books on that subject.

At what diameter do you remove the pith from a log before end sealing or leaving log unsealed? There are just too many correct answers to try to address all situations.

Where I live annual relative humidity, wood species available has given me both success and failures trying to dry wood. Normally logs six inches in diameter or less just cut, end seal, stack in my woodshed until get around to them. Over six inches will cut, split, end seal and stack.

I have a very simple plan, which varies a little with wood collected. I will normally cut and end seal wood wanted bowl or spindle turning. That wood goes into woodshed for months or years before turning. Was without a shed for awhile few years back and lost a lot my turning wood through checking fungus growth stored under a tarp.

First picture is a piece of Bradford Pear collected in Jan of this year, which is trying to bloom. Second and third are pieces of Dog Wood collected couple of days ago. The pen is Mulberry salvaged from bowl blank that checked so badly in storage. Actual pen looks better than photo.
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post #2 of 12 Old 03-28-2011, 12:11 PM Thread Starter
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Wood Equilibrium Moisture Content Table and Calculator
http://www.csgnetwork.com/emctablecalc.html

Wood never becomes totally dry there is always moisture in wood. Moisture content changes with relative humidity in air. Wood will gain and lose moisture until the day burned completely up in a fire. Applying the right finishing material will slow down moisture transfer but not completely stop it.
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post #3 of 12 Old 04-30-2011, 07:36 AM Thread Starter
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Drying wood is water removal process. One word that describes this process is evaporation! As wood dries, it shrinks get stronger and lighter in weight. When you fell a tree more than half its weight is water. We measure water in wood as a percentage called moisture content MC.

Wood dries from the outside in. If drying is not controlled wood, checks and cracks occur. Since water will leave the ends of a log 12 times faster than sides, we end seal.

Important to end seal wood soon as possible, and after cutting logs into manageable sizes.

A tree holds both free and bound water in its cells. When most of the free water is, almost gone MC said to have reached fiber saturation point FSP. MC is about 25 to 30 percent. Once FSP is, reach part of the wood starts shrinking. Bound water is chemically bound to cell walls evaporates much slower.

Before you can make something from your wood, sand, finish, wood must reach equilibrium moisture content EMC. Wood should be dried to a MC within 2% of its in-use MC.

Average in-use MC for interior use might be 6, 8, or 11 percent depending upon where you live. Average in-use MC for exterior use range from 12 to 16% MC.
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post #4 of 12 Old 04-30-2011, 07:42 AM Thread Starter
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Can anyone explain why? I cut a tree down for firewood, split and do not end seal, and store it in my woodshed. Nine months later will probably have a MC of about 20%. Nine years later that wood can still have a MC of 20%. Has nothing to do with wood only dries one inch per foot per year!
That wood has reached EMC, during the years in storage wood will gain and lose MC based upon relative humidity. Point here wood never really dries.
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post #5 of 12 Old 04-30-2011, 08:01 AM
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I'm not a rocket surgeon, but I DO know that ambient humidity affects the wood I turn Today.

We've had some pretty dry days here recently, RH < 20%, and on those days I MUST finish/seal projects immediately, or they will check and crack as I watch.

Most of the time, the RH here is well over 50%, and I have no problem turning and finishing fairly wet wood.

I've found that if I put a good finish on the piece, it will maintain it's integrity, even after spending time in the AC'd indoors(low RH), and when kept in the desert of south-central New Mexico(ditto).

Keep in mind, I'm relying on literally weeks of experience!

p

...ever notice how "I'm sorry" and "I apologize" mean the same thing, unless you are at a funeral..?
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post #6 of 12 Old 04-30-2011, 05:40 PM Thread Starter
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My approach to drying wood is simple and may seem caviler to many of you but it works for me. I want to work smarter than harder and limit times handle the same piece of wood.
Do not use a moisture meter or scales, although either one or both a great idea.

On logs less than 6 inches or less in diameter, do not worry about removing the pith, just end seal with either paraffin wax (Gulf canning wax) or latex paint and store. Over 6 inches in diameter will split, and not worry about the pith until cut or turn away. Over 10 inches in diameter will remove pith with chain saw.

Have never used a commercial end-sealing product (Anchor & Green Wood sealers) although think, they are great. I know a man that swears by oil based paint or varnish as an end sealer. Know a woman carver cuts her candle wax with mineral spirits and uses that.

Only use wax as an end sealer, never coat a complete piece of wood. Drying wood is a water removal process. Wood completely sealed in wax will retain moisture. As wood shrinks may or may not notice wax cracking, that’s okay if no end check occurring.

If you buy wood completely sealed in wax either turn right away or scrap wax from sides to allow moisture to escape. Wood merchants completely seal their wood in wax because they sell by the pound. Vendors selling to turners and carvers almost never guarantee MC of wood they sell.

That might not be true for wax emulsion sealers like Anchor & Green wood sealers. Apparently, they do allow moisture to escape. Only know what have read have no experience with the stuff.

Oil based paint, varnish, and poly will completely end seal logs.

Latex paint will allow moisture too escape only slows it down.

While end sealing important how you store wood also important. Need air circulation, protection from weather, and direct sun light.

Do not pay attention to over used rule like “one year of drying for every inch of thickness.” That rule does not take into account tremendous variations in species, density of wood or environmental conditions.
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post #7 of 12 Old 04-30-2011, 09:15 PM
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Here's what I use to dry bowls and small pieces of wood. My Unit was throwing this insulated box away so I brought it home, drilled some holes in the top, put in a fan and a heat lamp. I'm going to stand it on end and put more shelves in it but it works well for now.




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From Alaska to Florida who knows for how long.
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post #8 of 12 Old 05-01-2011, 07:28 AM Thread Starter
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I like your kiln that is what working smarter than harder all about!
Outstanding!
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post #9 of 12 Old 05-01-2011, 02:29 PM
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You get cracks in the wood when drying, from stress...literally, one portion of the wood dries faster than the rest, and the tension causes it to split. So the key is to dry it as evenly as possible.

My suggestion is that if you want to use this as stock for a table, you should have someone with a portable sawmill come over and slice the trunk into slabs for you. Then coat the ends with a sealer, when you stack the lumber for drying. (The attic space above your garage, or shop, would be a good place for this.) Depending on moisture content, it can take weeks, to months, to air dry oak to a desireable level. In the furniture industry we bring the moisture content down to around 6% to 8%, here in North America. This prevents most checking and other defects after the wood has been worked. It is important to note that air drying will not bring most lumber down to this moisture content level. Common practice is to air dry for a period and follow it up with kiln drying. Air drying red oak, at 4/4 slabs will bring it down to about 20% moisture content in most locations - how long it actually takes depends on where you live and what time of the year you start, but you can expect it to be around 4 to 8 months, at a minimum. Most woodworkers will give it a full year, for every inch of thickness, for best effect. Kiln drying also serves to help kill off all the little critters that live inside the wood, so, I would suggest you finish off with kiln drying. Talk to your kiln owner/operator about scheduling.. or you may opt to build one yourself. Heated kiln drying is the method that kills insects, using a humidification system is another way to dry lumber, but it will not kill the critters.

Check for Home and Gardening pergola plans or various plans for pergola.
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post #10 of 12 Old 05-01-2011, 05:16 PM Thread Starter
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Kiln drying just too expensive for most woodturners. Kiln operators do not like to put wood over two inches thick in their kilns. They do not like to mix species of wood too much. You risk case hardening putting thick turning blanks in a kiln.

Just because wood has been in a kiln does not mean it will not gain MC with change in relative humidity.

Basswood or pine decoy blanks four inches thick will dry in less than a year. A four-inch thick blank of Rosewood may take longer to dry without defects. Generally lower density wood take less time to dry than higher density woods.

Rough turning bowls and hollow forms speeds up dry, because you decrease (remove) amount of wood to dry. Building a simple kiln like Doug 1980 increases success rate and shortens drying times.

Pen turners have taken some really simple but effective ways to dry their pen blanks normally less than one inch thick or less by sixes inches long. Putting blanks in attics, car trunks, shelf over stovepipe, beer cooler kilns, and old cooking stoves just some methods used.

One reason say drying wood is more art than science for wood turners is because they deal with so many different species, and live all over the country. Cell structures different if wood comes from base of the tree vice crotch, and limbs. Woodturners often turn roots, reaction and burl wood that has some crazy cell structure. Mineral content can also vary within same species of wood.
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post #11 of 12 Old 05-01-2011, 05:25 PM Thread Starter
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Do woodturners need and use dimensional kiln dried lumber? Application like making pepper mills, mirrors, nut crackers just some of many things we make. Can also use air dried lumber but better know it is dry before you do. I have never bought wood for pens made.
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post #12 of 12 Old 05-09-2011, 07:28 AM Thread Starter
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I like this article for bold moves (risk) this guy takes turning wet bowls. Only thing stopped doing is cutting really wet wood on my bandsaw. Hate cleaning the blade. I have never had any luck leaving any portion of the pith, he does!

http://www.customwooddesign.com/turninggreenwood-1.html
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