Drying wooden in a photo voltaic kiln

My article “Construct Your self A Photo voltaic Kiln” in FWW #310 contains plans for the kiln I constructed and descriptions of the method of constructing it. However there was not sufficient room to get into the subtleties of working the kiln. That’s what I’ll cowl right here. First, nonetheless, I’ll clarify how I am going about sourcing materials appropriate for drying.

Discovering inexperienced lumber and logs

There are a number of methods to get inexperienced lumber to dry in your kiln. One is to purchase inexperienced lumber. You should purchase inexperienced boards for a lot lower than kiln-dried. Many sawmills will promote inexperienced lumber and so will sawyers with moveable mills. One good approach to discover small impartial sawyers is to contact firms that make moveable bandsaw mills—they’ll often have buyer lists accessible. Go down the record of native sawyers and get in contact; odds are you will discover some that promote inexperienced boards.
Another choice is to supply your individual logs and have a conveyable bandsaw mill come to you to noticed them into planks. For those who don’t have your individual supply for logs, they are often surprisingly simple to seek out. Tree service firms are a great place to start out. For those who discover a tree service working in your space, discuss to them—they’ll generally be completely satisfied to drop off just a few logs and save themselves having to cope with them.

Once I first began milling logs, I put an advert on Craigslist to promote just a few inexperienced boards to offset the price. I used to be shocked how many individuals contacted me from these adverts to attempt to promote and even give me logs. Individuals could have a tree or two eliminated and don’t wish to see it go to firewood or the landfill. After phrase will get out that you simply do that form of factor and have a photo voltaic kiln, you’ll have loads of folks wanting to offer you logs. I say no to extra logs than I take.

I rent a neighborhood sawyer to return lower the logs for me. He owns a WoodMizer bandsaw mill that may noticed as much as a 30-in. log. The sawyer is nice to work with and fees me by the hour. Among the logs come from my very own property and others got to me. I’ve by no means paid for logs, however I do generally pay to get them transported.

Working with the sawyer, I can mill logs precisely how I need them. I will be choosy about lower orientation to get one of the best grain attainable. Once I first began having logs milled, I might lower 4/4, 5/4, 6/4, and eight/4 boards. I quickly discovered this too sophisticated, as a result of while you stack the lumber within the kiln all of the boards in a selected layer must be the identical thickness. With so many thicknesses I used to be all the time quick a board to fill out a layer or had one board too many. Today I mill simply 5/4 and eight/4 inventory except I’ve a challenge deliberate that requires another dimension. This makes stacking and holding issues tidy a lot simpler.

Proper after the logs are milled, I sweep them clear of sawdust and take away the bark. The bark virtually falls off a freshly lower board, however on uncommon events I’ll use a drawknife to take away it. I fastidiously examine every board for bugs or injury. Any boards which are questionable or odd-shaped I’ll promote inexperienced for very low-cost. No cause to waste area within the kiln for one thing I received’t use. Whenever you mill your individual materials, you may afford to be very choosy.

To actually sanitize lumber and kill any bugs it may be harboring, the wooden wants to achieve a core temperature of 135°. Most occasions the photo voltaic kiln will get to that temperature and above just a few days in a cycle. However I don’t fear about it an excessive amount of as a result of I’m very cautious about what I dry. The bark is the primary place for bugs to dwell and it will get eliminated lengthy earlier than it goes into the kiln. The boards are very clear, and I’ve by no means had a difficulty.

Loading the kiln

I designed my kiln with giant double doorways to make loading it as simple as attainable. I’ve a tractor, and my intention was to load and unload the entire lumber stack in a single go utilizing forks on my tractor. Because it seems, though I might do this, I don’t. As a substitute, I favor to see every board because it goes into the kiln after which once more when it comes out. When milling I don’t have the time to look over every board and this offers me the possibility. When unloading I get to see how they dried and might begin to kind the boards in my head.

When loading the boards into the kiln I modify the sliding bunks with stickers I constructed onto the ground. The usual for stickering is often 12 in. to 18 in. aside. I am going with 18 in. aside for higher air move, and I’ve been pleased with the outcomes. Contained in the kiln I exploit dried hardwood stickers solely, making them ¾ in. sq.. I make them within the store each time I’ve scrap materials, so I’ve them in a number of species. As I add layers of boards to the stack of lumber, I preserve the stickers in a pleasant, straight, vertical line proper up the stack. You possibly can dry boards of various thickness in the identical load, however every layer of boards must be the identical thickness. I preserve every layer as tight and neat as attainable.

The placement of your stack contained in the kiln is essential. You need about 12 in. of clearance from the back and front partitions. This provides you with loads of airflow. By way of drying, the ends of the stack will be as near the partitions (left and proper) as you need. Nevertheless, it turns into very tough to load and unload the kiln if the area is simply too tight there. My kiln might match planks 10-½ ft. lengthy, however I lower my logs to a bit of over 8 ft. This provides me further area within the kiln and makes it a lot simpler to stack the boards.

The highest of the stack will get a further layer of stickers. Then I cowl the stack with plywood I painted flat black. This shades the stack from the direct solar and prevents it from getting solar bleached. Simply bear in mind to not block the 12 in. of air move on the back and front of the stack. On prime of the painted plywood, I stack some cement blocks that I’ve additionally painted black. These sit within the direct solar and act as a incredible warmth financial institution. In addition they preserve the black plywood shading in place. I don’t suppose the added weight prevents twisting or cupping; when wooden desires to maneuver it’s going to maneuver.

With the stacking performed, I hold the followers again on their French cleats, then staple baffling materials between the underside of the followers and the highest of the stack in addition to between the ends of the stack and the aspect partitions. The baffling retains the air flowing by the stack and never round it. For the baffling I’ve been utilizing some leftover vapor barrier. When that runs out, I plan to have a extra reusable system that may be rolled up out of the way in which when loading and unloading. A black materials could be preferrred for this.

Working the photo voltaic kiln

As soon as the lumber and followers and baffle are in place, I take a moisture studying on the thickest board within the middle of the stack. I write that studying and the date in chalk on the plank I examined. Then I plug within the followers (blowing towards the roof) and shut the doorways.

The photo voltaic kiln dries lumber in light cycles: When the solar is out the followers flow into the heated air, which absorbs moisture from the wooden. At evening the lumber cools means down, the followers are off, and a few of that expelled moisture within the air reabsorbs into the wooden.

I’ve generally taken planks proper off the mill and put them straight into the kiln, and different occasions I’ve stickered fresh-sawn planks for just a few months of air drying outdoors earlier than placing them within the kiln. My drying course of is easy and the identical for each. I begin with the vents closed all the way in which for one sunny day to get the wooden acclimated to the warmth. It is going to quickly seem like a rainforest contained in the kiln if the wooden is useless inexperienced. If I consider it, I open the vents all the way in which up at evening to let moisture out and shut them the subsequent morning. Even closed there shall be some air move from leaks which are inconceivable to stop. You possibly can go a pair extra days with the vents closed, however you will need to verify inside as a result of mildew can begin to type.

After this preliminary acclimation, I open every vent roughly one inch. At the start, I’ll look within the kiln the primary few days and ensure there isn’t any mildew forming. Water would possibly begin pooling on the ground; I simply go away it, for the reason that kiln will dry it will definitely. If I discover any mildew forming, I’ll open the vents up one other ½ in. This may range relying on the dimensions of your vents, the season, and the way moist the wooden was while you began. As soon as I’m completely satisfied there isn’t any mildew forming, I go away the vent setting till the wooden reaches 20% moisture content material.

There are just a few steps you may take to regulate the drying charge of the photo voltaic kiln. The primary possibility (and the one one I’ve used) is to open and shut the 4 vents within the again. In concept, in case your kiln have been completely sealed and also you closed the vents, zero moisture might escape. The air inside would develop into totally saturated, however there could be no means for the moisture to flee the kiln. Then at evening the moisture would all finally be reabsorbed by the wooden. Opening the vents permits moisture to be vented from the kiln out into the surface air.

One other approach to modify the drying charge is to cowl a portion of the roof. Doing this lowers the temperature contained in the kiln and slows the drying. Shutting off the followers throughout the warmth of the day may even gradual the drying charge.

To hurry the drying charge, you may think about loading much less wooden into the kiln. With much less mass to warmth and a better photo voltaic collector-to-lumber ratio, the kiln will get hotter and the drying goes sooner. (This relationship is essential to recollect when you could have an empty kiln. With no mass inside, the kiln will get a lot hotter and the warmth can injury the followers and even the roof panels. This may be solved by masking the roof with a tarp to maintain the solar out.)

Monitoring moisture within the kiln

There are a number of methods to observe the every day moisture lack of the wooden within the kiln. I’ve a Delmhorst J-2000 moisture meter that has 2-in. pins I can pound into the wooden to get an correct studying. Pinless meters could be positive to verify the preliminary drying charges within the kiln however don’t penetrate deep sufficient to precisely inform you when the board is totally dry. Some folks make pattern boards to place within the kiln and weigh them periodically to observe the drying charge utilizing the “oven technique.”

Once I first used the kiln, I fastidiously monitored the every day drying charges and cross referenced the secure drying charge charts. I don’t anymore. The dimensions of my kiln, my location, and the species I dry have been all the time underneath the secure drying charges. Now I simply go away the vents open about an inch till the boards attain a moisture content material of about 20%. Many of the defects which are going to occur as a result of drying course of will happen because the wooden goes from inexperienced all the way down to 20-22% MC. As soon as the wooden has reached 20%, I open all of the vents about 4 in. or so. It’s essential to recollect there’s a tradeoff: The extra you open the vents the decrease the interior temperature shall be. A plank wants warmth in addition to air move to dry, and that’s very true for the middle of the board.

I bought an ordinary low-cost wi-fi climate monitoring station that got here with three distant displays. I place one monitor contained in the entrance portion of the kiln, a second contained in the rear of the kiln, and the third outdoors the kiln. The displays ship temperature and humidity data to a digital show that I preserve in our kitchen. I exploit this knowledge to fine-tune my vent settings. The displays most likely aren’t extremely correct, however they’re constant sufficient.

The perfect I’ve been capable of obtain is 50° hotter than the surface air in the summertime and as much as 60° hotter within the winter. The roof being just a few levels steeper than my latitude accounts for the distinction. My distant monitoring station maxes out at 140°, and I’ve maxed it many occasions in the summertime months. When the wooden is inexperienced, the humidity studying can typically be 100%. Once I discover it’s down round 10% for a number of days, I begin taking extra moisture content material readings straight from the boards, as a result of they’re getting near dry.

How lengthy to dry a load of lumber?

Drying time relies on a number of elements: outdoors temperature, variety of sunny days, how effectively the kiln is insulated, thickness of fabric, and even species. For constructing inside furnishings, you ideally wish to get the moisture content material between 6% and eight%. Once I attain 8% or underneath, I’m able to unload the kiln. I’ve gotten it as little as 7%, nevertheless it appears to take a disproportionately very long time to get there and eight% is ok for my store.

My photo voltaic kiln takes about 4-5 heat sunny summer season weeks to dry a load of 5/4 inexperienced wooden to eight%. I’ve dried cherry, walnut, ash, purple maple, birch, and oak. The standard of lumber that comes out all the time amazes me. Positive, the pith items will break up and there are some finish checks right here and there. However usually the boards come out comparatively flat and retain most of their colour. They machine effectively and work nice with hand instruments. In my expertise wooden from my kiln behaves a lot better then commercially dried materials and strikes little or no when ripped if in any respect.

Mixing species, and even thicknesses, within the photo voltaic kiln is ok. It’s worthwhile to preserve the thickness inside the layers the identical however apart from that I’ve dried 8/4 proper on prime of 5/4 materials. In fact, 8/4 will take longer to dry so I both go away it in for a second cycle, or simply go away the entire stack within the kiln till the 8/4 is completed. The photo voltaic kiln won’t over-dry the 5/4 materials. The kiln may be very forgiving and is generally a set-it-and-go system.

There are methods to switch your photo voltaic kiln to hurry up dry time. You would add a second layer of your roofing materials and fasten it contained in the kiln to the underside of the rafters. This may improve the warmth within the kiln by growing the photo voltaic collector. You would additionally add some supplemental warmth to the kiln in addition to run a dehumidifier. You would need to pay a lot nearer consideration to the secure drying charges with any of those modifications.

My followers are powered by small photo voltaic panels, so when the solar is out, they spin. The photo voltaic panels imply I don’t have to run energy to the kiln, and the method works fairly effectively. However one approach to make my system extra environment friendly could be so as to add a timer to the followers. Ideally, the followers wouldn’t begin to spin till the kiln heated up sufficient within the morning solar. The inside will warmth a lot sooner with out the followers operating. And after the solar goes down the temperature nonetheless stays excessive contained in the kiln for a number of hours the place you’ll profit from the followers nonetheless operating. This may require me to arrange a battery system; if I did have energy within the kiln, I might be utilizing a timer.

Remaining ideas

One apparent benefit to having a photo voltaic kiln is the price financial savings. However for me it’s so far more than that. My favourite half is utilizing the sources round me to make furnishings. In New England we’re fortunate and have hardwoods throughout us. It all the time used to hassle me to go to a lumberyard and buy oak, maple, ash, cherry, or different species that develop regionally. How ridiculous it felt to purchase oak which may have come from a number of states away and been trucked to a mill, then trucked to my native lumberyard. Typically, on the way in which dwelling from the lumberyard, I might drive previous an oak tree being eliminated to clear energy strains or make means for building. What a waste of native sources to have it go to firewood, mulch, or the landfill.

One essential factor to notice: There may be plenty of labor concerned in milling logs and loading and unloading the photo voltaic kiln. Switching over the masses within the kiln will be performed alone, nevertheless it’s a lot sooner with two folks. I’ve the sawmill are available about 4 occasions a yr, and having just a few folks serving to on these days makes for a way more nice expertise. Anybody who helps me invariably goes dwelling with a pleasant stack of boards from the earlier load I dried.

My photo voltaic kiln has been in use for 4 years and has dried about 4,000 board ft. Over this time, I’ve discovered that the photo voltaic kiln is forgiving, and it could be tough to break your lumber. I additionally discovered to mill at the least one kiln load forward. This fashion, the subsequent stack will be air drying whereas it’s ready for a flip within the kiln. This begins the drying course of and shortens the time wanted within the kiln. Woodworking mates of mine actually just like the photo voltaic kiln as effectively. I can’t presumably retailer and use all the pieces I mill, so I’ll typically make trades. The price of the kiln might probably be offset by promoting dried boards. Individuals have additionally requested to lease area within the kiln to dry a few of their very own materials. Planning your load schedule maximizes the yield. I attempt to get two to 3 masses by from spring to fall, and a further load stays within the kiln all winter.

Does each woodworker want a photo voltaic kiln? In fact not. However when you have a ardour for woodworking, a curiosity for the supplies you utilize, and an appropriate place to construct a photo voltaic kiln, I like to recommend giving it some thought. I’ve milled and dried a historic tree, a household tree, timber headed to a landfill, broken timber, and timber that have been simply in the way in which of one thing else. Now each challenge I make has a narrative to inform. I bear in mind the tree, the place it got here from, and the way I obtained it. I bear in mind milling the tree. Typically, I’ll bear in mind seeing the precise board coming off the mill.