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Mike Holbrook
07-23-2016, 11:27 AM
I like harvesting and drying smaller pieces of wood for making furniture. I am also interested in harvesting and using smaller limbs, shrubs and trees, maybe with the bark still on. I have books by Peter Galbert and Drew Langsner, chair & furniture makers, with designs for drying small pieces for chairs, maybe table parts. Most of these designs are for indoor kilns.

I am interested in building a more insulated outdoor kiln, capable of handling a little larger pieces, say 5-6 feet long. I am moving to the North Georgia mountains to a log home. My shop will be in a large two car garage, with an apartment/guest house over it. There is a porch/deck at the rear exit to the garage, which is actually two stories, with a roof over the top story. I am thinking about building a kiln to reside on or next to this porch. I am thinking about a small electric heater or intense lights to warm the interior to a thermostat controlled level, under 200 degrees.

I am considering building the kiln out of rock/ brick/ engineered rock or maybe galvanized/painted metal or some combination of those materials. Leaving wood in a wood kiln, even a "fireproofed" wood structure, for long periods makes me nervous. I also have my doubts about how well such a structure would stand up to outdoor elements. I am wondering if anyone on this forum is familiar with a design they can point me towards or advise me on?

John TenEyck
07-23-2016, 2:38 PM
Let me start by saying I built a dehumidification kiln about 15 years ago, following the general plans in a FWW article from maybe 20 years ago. I can point you to the correct issue if you are interested. The kiln is a box made from 2 x 4's and plywood, caulked and painted on the inside, and insulated with 1-1/2" foil faced foam on the outside. My version holds 275 BF of lumber up to 8' long and 30" wide. It runs at 110F and is heated by nothing more than 3, 100W incandescent light bulbs. There is a hi temp. switch that will trigger an alarm, but the there is just about no way this thing could ever over heat. A blower to circulate the air and a household dehumidifier are the other major components. A simple control system maintains control of temp. and RH. There even is provision for adding moisture back at the end of the drying cycle to eliminate case hardening.

I air dry my green milled lumber for at least 4 months and usually longer before putting it in the kiln. Where I live the EMC will get down to about 12 - 14% outside. Starting with that it takes 2 - 3 weeks to dry it in the kiln down to 6 - 7% MC. It costs less than $20 to dry a load of wood. I built the thing for less than $300.

IMO you do not want to build a big heavy masonary structure for a kiln, nor do you want to run it up to 200F. That makes everything more complicated and expensive with the only benefit being a high temp. kiln will crystallize pine sap. You would need an excellent control system, and knowledge of how to use it, to operate a high temp. kiln. If you keep it light and well insulated, and run it at low temperature, it won't cost much to build or operate a kiln and it will be inherently safe.

The absolute safest thing you could build would probably be a stand alone solar kiln, sited well away from any other buildings. Solar kilns operate at relatively low temperature, too, and some people build them against the back of a barn, etc..

John

Mike Holbrook
07-24-2016, 12:54 PM
Appreciate your thoughts John.

In his new book Galbert says he runs his kiln for chair parts at 140. I seem to recall kilns at chair classes being run closer to 200. I imagine that kilns in classes may be run that high because they are being opened constantly, which would be the only reason I might turn a kiln up that high, even for a relatively short period.

I think much of the wood I will be working for chair and table legs,..is much less sensitive to shrinkage/splitting due to the shape and size of the pieces. Chair classes start with green wood and in 5-7 days end up with pieces that are relatively stable. Galbert says he leaves the green parts he is working out in his shop for two or three days then puts them in the kiln, which is about what happens in a chair class as well. I find that once a log is quartered it is less likely to split. Galbert mentions this in his book too. I think it has to do with a larger part of the radial & tangential mass of the wood being able to adjust to the surrounding air & humidity. Certainly lumber with its major exposure of radial plane wood would logically have more potential issues than the smaller round or square pieces typical of chair stock.

I am still considering whether or not I want to dry green lumber. I suspect a kiln full of lumber would make it harder to dry smaller parts, due to the excess moisture. If I were to dry lumber I might build a separate kiln for it.

I thought about a solar kiln for a good while. I don't have a good location for one on my new lot, which is covered in tall hemlocks. I am more interested in drying smaller pieces up to 50-60" long in a matter of days or weeks.

John TenEyck
07-24-2016, 1:17 PM
Small cross section parts like those used in a chair will tolerate faster drying than a wide board. Green sawn lumber (wide boards) will not tolerate rapid drying. Commercial kilns start at 100F or so with very high humidity to slow the drying rate enough to prevent checking or worse. It takes many days to dry a load of 4/4 lumber, weeks to dry 8/4. For a hobbiest it's just a whole lot easier to sticker a pile of green lumber outdoors and let Mother Nature take care of the initial drying. Once the MC is down below the fiber saturation point, then you can be more aggressive about bringing it down to what's needed for furniture making.

I know nothing about what's needed for chair stock, however. Sorry.

John

Mike Holbrook
07-24-2016, 8:54 PM
Right John,

My interest in drying smaller pieces for chairs is probably not representative of the majority of those drying lumber.

I think your suggestion of stickering green lumber is probably my best option. The area I will be living in, North Georgia mountains, has actual sawmills that I believe I can acquire rough sawn, local lumber from at reasonable rates.

I have a two story decked area, with a roof, behind the garage area my shop will be in. It may be a good place to dry rough sawn lumber, if I can keep my pack of GSD's, German Shepherd dogs, from eating it. They love big sticks, which can be a problem.

Scott T Smith
07-28-2016, 5:03 AM
Mike, there is a lot involved with kiln drying. To learn more, I would recommend that you do a search and download the following:

1. Drying Hardwood Lumber, by Gene Wengert
2. The USDA Drying Eastern Hardwood Lumber (https://naldc.nal.usda.gov/naldc/download.xhtml?id=CAT87208771&content=PDF)

Drying schedules vary based upon species, thickness and moisture content. The two publications referenced above will greatly assist you with understanding the process.

Scott