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Home Made Kiln

Do you have a home made kiln?


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Emiliano Achaval

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I found a flower "Lei" display case. Its the same as a beverage display case, with glass in the front. The engine still runs, but the air its not cold, temperature goes up to 74.5. On the inside, on the ceiling there is a fan that moves the air, recirculates it inside. I'm thinking if I drill a hole above it from the outside the fan might help me with the drying process. I have read Cindy Drozda PDF on her kiln. She doesn't say how big her holes are, or how many, and where... A friend told me make them 4 inches wide, one above, one below, and have the light bulb below. The case is very tall, like over 6 feet, only 2 shelves, I will add a few more.
So, my questions are: how many holes, both sides?, opposites sides, what size holes? Is the fan inside too much air movement? I have called an appliance repair guy, he will disconnect the motor. The door has a nice light, but fluorescent, and I dont think it gets hot enough... Most people seem to be using a 60 watt incandescent light bulb... I searched the forum and did not find anything about this...
Since I got into box making, want to make sure my wood is dry, and I want to dry wet wood faster... Thank you in advance for your response. Aloha from Maui
 
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Look for thrown out dishwasher, you can have mine if you come get it
 
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I found a flower "Lei" display case. Its the same as a beverage display case, with glass in the front. The engine still runs, but the air its not cold, temperature goes up to 74.5. On the inside, on the ceiling there is a fan that moves the air, recirculates it inside. I'm thinking if I drill a hole above it from the outside the fan might help me with the drying process. I have read Cindy Drozda PDF on her kiln. She doesn't say how big her holes are, or how many, and where... A friend told me make them 4 inches wide, one above, one below, and have the light bulb below. The case is very tall, like over 6 feet, only 2 shelves, I will add a few more.
So, my questions are: how many holes, both sides?, opposites sides, what size holes? Is the fan inside too much air movement? I have called an appliance repair guy, he will disconnect the motor. The door has a nice light, but fluorescent, and I dont think it gets hot enough... Most people seem to be using a 60 watt incandescent light bulb... I searched the forum and did not find anything about this...
Since I got into box making, want to make sure my wood is dry, and I want to dry wet wood faster... Thank you in advance for your response. Aloha from Maui


Emiliano,
I would like to see a picture of the case you are referring. Having not seeing it you can drill 2" holes in the side towards the top and bottom. You don't have to use all what you drilled by making a cover for them. Rotate the cover for full open to partial open. The fan inside is a very good idea to keep air moving over your blanks. This helps to stop mold from developing and helps keep surface moisture from staying on the wood. My dehumidifier kiln, albeit much larger, has three fans in it.

A light bulb heat source is an Ok method however those types of incandescent bulbs needed will become obsolete sooner rather than later. You can pick up a small 120 amp oven heating element for around $15. Just make sure sure you mount it safely as not to start a fire. I have mine mounted in an old metal computer case. Hook it up through a thermostat for better heat control. The light bulb method works just make sure you keep it 1" off the bottom so any water that accumulates won't cause a problem.

Just to give you something to compare to my kiln is 8' wide x 3' deep x 7' tall and has insulated 2x4 walls, head and floor. I also use a dehumidifier.
 
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Not sure if this will help you but here's a couple pics of a kiln I did for some powder post beetle critter elimination on cherry lumber a few years ago. 1/2" plywood skin lined with thin insulation panels from the big box store. I used a couple 250 watt infra red bulbs with a fan on one end & on casters for mobility. Drilled a hole in one corner for any water drainage and sealed it up with a rubber stopper. Made a little plexiglass observation window so I could see a few different thermometers stuck in a piece of scrap lumber that would read internal lumber temp. This box held just shy of 100 bf on lumber.

kiln5.jpg

kiln4.jpg


kiln6.jpg
 
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Nice project, Dave. My problem is having enough space for something like that or even an old dishwasher.
 

Emiliano Achaval

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Emiliano,
I would like to see a picture of the case you are referring. Having not seeing it you can drill 2" holes in the side towards the top and bottom. You don't have to use all what you drilled by making a cover for them. Rotate the cover for full open to partial open. The fan inside is a very good idea to keep air moving over your blanks. This helps to stop mold from developing and helps keep surface moisture from staying on the wood. My dehumidifier kiln, albeit much larger, has three fans in it.

A light bulb heat source is an Ok method however those types of incandescent bulbs needed will become obsolete sooner rather than later. You can pick up a small 120 amp oven heating element for around $15. Just make sure sure you mount it safely as not to start a fire. I have mine mounted in an old metal computer case. Hook it up through a thermostat for better heat control. The light bulb method works just make sure you keep it 1" off the bottom so any water that accumulates won't cause a problem.

Just to give you something to compare to my kiln is 8' wide x 3' deep x 7' tall and has insulated 2x4 walls, head and floor. I also use a dehumidifier.
Thank you for your reply!! Today I drilled 2 holes at the bottom, 2 at the top. Each is 1 5/8 wide. I will take a picture tomorrow... I had to still light bulbs from my house, and related them with LED, went to ACE hardware and they dont sell old light bulbs anymore!! Someone suggested a heating rod for inside a safe... Will that work? So you think the fan on the ceiling is not too much air flow? Cindy drozda has 2 one inch holes below, and 2 above... Appreciate your help. Aloha.
 

Emiliano Achaval

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Not sure if this will help you but here's a couple pics of a kiln I did for some powder post beetle critter elimination on cherry lumber a few years ago. 1/2" plywood skin lined with thin insulation panels from the big box store. I used a couple 250 watt infra red bulbs with a fan on one end & on casters for mobility. Drilled a hole in one corner for any water drainage and sealed it up with a rubber stopper. Made a little plexiglass observation window so I could see a few different thermometers stuck in a piece of scrap lumber that would read internal lumber temp. This box held just shy of 100 bf on lumber.

kiln5.jpg

kiln4.jpg


kiln6.jpg
Nice one!! But... I can peek into mine! LOL. Love the glass door... Interesting choice of lights! I guess they are not too hot?? Is that heating lights? Thank you for taking the time to answer. Aloha
 

Emiliano Achaval

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Not sure if this will help you but here's a couple pics of a kiln I did for some powder post beetle critter elimination on cherry lumber a few years ago. 1/2" plywood skin lined with thin insulation panels from the big box store. I used a couple 250 watt infra red bulbs with a fan on one end & on casters for mobility. Drilled a hole in one corner for any water drainage and sealed it up with a rubber stopper. Made a little plexiglass observation window so I could see a few different thermometers stuck in a piece of scrap lumber that would read internal lumber temp. This box held just shy of 100 bf on lumber.

kiln5.jpg

kiln4.jpg


kiln6.jpg
Sorry, I didn't read before my first reply. I will try those infrared light... And... you have a window!! Aloha
 

Bill Boehme

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Infrared lights are made for things like keeping food hot at restaurants. They might be OK for baking wood to kill bugs. It looks like the meat thermometer is reading 180 degrees. I think that would be way too hot for a drying kiln. For a box of the size of yours I think that an oven lightbulb Would be about right. They are specialty tungsten with a rating of about 40 watts. They are still available because CFL and LED lights wouldn't survive long in an oven. The temperature should be warmer than outside air, but not blazing hot.
 

Emiliano Achaval

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Emiliano,
I would like to see a picture of the case you are referring. Having not seeing it you can drill 2" holes in the side towards the top and bottom. You don't have to use all what you drilled by making a cover for them. Rotate the cover for full open to partial open. The fan inside is a very good idea to keep air moving over your blanks. This helps to stop mold from developing and helps keep surface moisture from staying on the wood. My dehumidifier kiln, albeit much larger, has three fans in it.

A light bulb heat source is an Ok method however those types of incandescent bulbs needed will become obsolete sooner rather than later. You can pick up a small 120 amp oven heating element for around $15. Just make sure sure you mount it safely as not to start a fire. I have mine mounted in an old metal computer case. Hook it up through a thermostat for better heat control. The light bulb method works just make sure you keep it 1" off the bottom so any water that accumulates won't cause a problem.

Just to give you something to compare to my kiln is 8' wide x 3' deep x 7' tall and has insulated 2x4 walls, head and floor. I also use a dehumidifier.
If is not too much trouble, could you take a picture of the heating element box and thermostat? What is the ideal temperature? Thank you in advance!!
Infrared lights are made for things like keeping food hot at restaurants. They might be OK for baking wood to kill bugs. It looks like the meat thermometer is reading 180 degrees. I think that would be way too hot for a drying kiln. For a box of the size of yours I think that an oven lightbulb Would be about right. They are specialty tungsten with a rating of about 40 watts. They are still available because CFL and LED lights wouldn't survive long in an oven. The temperature should be warmer than outside air, but not blazing hot.
Great tip Bill!!! Just love this AAW forum... I will post pictures of my contraption tomorrow. Aloha
 

Bill Boehme

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You might check with your fellow Islander, Kelly Dunn. He uses a kiln and says that is the only way that most wood can be dried in the humidity there. Fortunately, I don't have to do anything special beyond putting some Anchorseal on the wood.

BTW, Kelly is currently out of pocket, off to the mainland to attend his daughter's graduation.
 

Emiliano Achaval

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I rough turn most of my work. Then it goes on a shelve for a minimum of six months... Super bone dry here is 12.4 %... I dried some apple wood in the microwave in the house. Wife almost kill me, lol, but thats another story. The apple was bone dry. Then we had a Kona storm. It actually gained some weight back! So, I dont think it makes sense to worry about drying too much, unless you have to send it to the mainland. Then it is a good idea to throw it in the kiln, get it out, and run to the post office... Cindy Drozda actually texted me back and told me how her kiln is... I have never felt the need to dry the wood, but now i'm chasing threads daily, and the wood has to be bone dry... I'm off to Hilo for the opening of the 19th annual woodturning exhibition. I will be doing a demo on chasing threads. I'm sure I will see Kelly, I will ask him about his kiln... I appreciate your help Bill. Aloha
 
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Glass is a very poor insulator. For more heat and less energy spent, cover the unit with a shipping blanket or insulation blanket. I usually start all my drying at 90 degrees then build from there. I also have a small desk size fan for air circulation.
 
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As for lightbulbs—you can usually get 60 or 100 watt rough service bulbs at most hardware stores. I don't know much about kilns, other than talking to a few small operators. Most kilns for lumber work between 120 and 180° F.

An alternate to heat is to remove moisture from the air. I use a 10' X 12' insulated shed as a kiln of sorts...and I don't use heat, I use a dehumidifier. I see that wood dries faster with heat, but in my experience drying bowls of softwoods and softer hardwoods, I don't want to dry them too fast. But that's just me, and my conditions and wood species are very different from yours or anyone else on this forum.

One things is for sure: monitor your wood carefully. Nothing worse than ruining a bunch of blanks. Do some experimenting on blanks that aren't special to see how far you can push it. As an example, I've learned that I can dry mountain ash in roughly one quarter of the time of hemlock. Strait grained mountain ash is almost impossible to crack, and hemlock will crack in mere hours in a dry room. It's an adventure!
 
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Sorry it would be difficult to get a picture of the heating element. I have a tunnel in the back of the kiln where it is and the fans blow over it. I would have to dismantle a lot of things to get a picture of it. I heat mine to 95 degrees to start. as the wood dries I will go to 100, 105 until dry. If there are bugs, eggs or larvae then run it to 120 to 130 for two days, after wood is dry, and that will kill any insect issue. With my kiln a try to pull a gallon of water a day. Smaller kiln less water per day. The wood area in my kiln is 6' x 2' x 6'. You can calculate that square footage to yours and then run a calculation for how much water to pull every day from yours. At the end of the drying cycle the water pulled per day drops quickly that last week. I can dry a kiln load, depending on how wet the wood was when going in, in about 4 to 5 weeks. They are all bowls ranging in size from 18" to 7" in diameter. I have very little loss and what I do lose I can pretty much tell you as I load which ones I'll lose because they have a defect of some sort. I use a more expensive commercial thermostat on mine so It probably wouldn't useful to you. A household thermostat would work or oven thermostat. I don't know how big the fan is but I doubt not would be to much. Remember the kiln has a lot of humidity in it so the fan is blowing humid air around the blanks so it isn't like the fan is drying the wood it is just moving air around the blanks. You control the moisture loss by how much you open the holes or in my case how much I run the dehumidifier.
 

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Sorry it would be difficult to get a picture of the heating element. I have a tunnel in the back of the kiln where it is and the fans blow over it. I would have to dismantle a lot of things to get a picture of it. I heat mine to 95 degrees to start. as the wood dries I will go to 100, 105 until dry. If there are bugs, eggs or larvae then run it to 120 to 130 for two days, after wood is dry, and that will kill any insect issue. With my kiln a try to pull a gallon of water a day. Smaller kiln less water per day. The wood area in my kiln is 6' x 2' x 6'. You can calculate that square footage to yours and then run a calculation for how much water to pull every day from yours. At the end of the drying cycle the water pulled per day drops quickly that last week. I can dry a kiln load, depending on how wet the wood was when going in, in about 4 to 5 weeks. They are all bowls ranging in size from 18" to 7" in diameter. I have very little loss and what I do lose I can pretty much tell you as I load which ones I'll lose because they have a defect of some sort. I use a more expensive commercial thermostat on mine so It probably wouldn't useful to you. A household thermostat would work or oven thermostat. I don't know how big the fan is but I doubt not would be to much. Remember the kiln has a lot of humidity in it so the fan is blowing humid air around the blanks so it isn't like the fan is drying the wood it is just moving air around the blanks. You control the moisture loss by how much you open the holes or in my case how much I run the dehumidifier.

About a dozen years ago when Trent Bosch was teaching classes at our club he did a presentation on the kiln that he used for drying bowls. From your description, your kiln sounds very similar.
 

Emiliano Achaval

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I had to turn off the light today. The 75 incandescent light bulb proved to be too much. Some of the wood was checking bad. Bill Boheme gave me a great tip, I bought an oven light bulb. It is incandescent, heavy duty, 40 watts. Thank you Bill!! Temperature was 85.2 with the 75 watts. All the wood, obviously, lost several ounces of weight in one day!
Thank you everybody that has taken the time to help me. Greatly appreciated. Aloha
 

Emiliano Achaval

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Sorry it would be difficult to get a picture of the heating element. I have a tunnel in the back of the kiln where it is and the fans blow over it. I would have to dismantle a lot of things to get a picture of it. I heat mine to 95 degrees to start. as the wood dries I will go to 100, 105 until dry. If there are bugs, eggs or larvae then run it to 120 to 130 for two days, after wood is dry, and that will kill any insect issue. With my kiln a try to pull a gallon of water a day. Smaller kiln less water per day. The wood area in my kiln is 6' x 2' x 6'. You can calculate that square footage to yours and then run a calculation for how much water to pull every day from yours. At the end of the drying cycle the water pulled per day drops quickly that last week. I can dry a kiln load, depending on how wet the wood was when going in, in about 4 to 5 weeks. They are all bowls ranging in size from 18" to 7" in diameter. I have very little loss and what I do lose I can pretty much tell you as I load which ones I'll lose because they have a defect of some sort. I use a more expensive commercial thermostat on mine so It probably wouldn't useful to you. A household thermostat would work or oven thermostat. I don't know how big the fan is but I doubt not would be to much. Remember the kiln has a lot of humidity in it so the fan is blowing humid air around the blanks so it isn't like the fan is drying the wood it is just moving air around the blanks. You control the moisture loss by how much you open the holes or in my case how much I run the dehumidifier.
I will have the appliance guy disconnect the pump, but I want to keep the fan. I can turn it on during the day, when I'm in the shop. I believe it will help, and you have proven my point. Thank you for your help.
 
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I had a portable dehumidifier in the basement of a house many years ago. It pulled the air in and let it empty into a bin that I emptied about once a day or you could hook a section of garden hose to hit and drain it into a floor drain.
 

Bill Boehme

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A couple years ago I kept records on the weight of a bunch of roughed out bowls that started out very wet and coated with Anchorseal. For the first few days as Dale Bonertz also said about the bowls in his kiln, there is a huge amount of water lost. For the first couple days some of the water was from the Anchorseal. Initially, the rapid weight loss is free water being evaporated. After the free water is gone, the bound water starts to evaporate, but there is a lot of overlap because the outer part will be losing bound water while the inner part still has free water. There is a lot of water lost in the first week, maybe half as much the second week, half again the third week. After a month, it is mostly bound water that is slowly evaporating. Warping and cracking occur when bound water starts to leave so I don't rush this stage. I keep these rough turned pieces in my air conditioned garage during the summer. At the end of three months the water loss is very slow and for a lot of wood, it can be finish turned with little or no warping. However, even bone dry wood may warp as it is finish turned since removing wood upsets the balance of internal stresses that were in equilibrium.
 

Emiliano Achaval

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About a dozen years ago when Trent Bosch was teaching classes at our club he did a presentation on the kiln that he used for drying bowls. From your description, your kiln sounds very similar.
Bill, why do you think what I'm doing is not more widely used by woodturners? I know its easier to leave things on a shelve for 6 months, but for box making I believe its going to help me a lot... Also, some of the wood I got in exchange was kiln dry. Boy!! Nastiest driest wood ever, cocobolo, made a mess too, orange dust all over... The box I did today was from an old Kiawe fence post, cut over 20 years ago, dried naturally, my chasers were making beautiful tiny shavings, a beautiful sight that gives this grown man goosebumps haha. Did I tell you the oven light is working perfectly!! Best tip yet so far out of this thread!! The 40 watts is just right!! Aloha from Maui.
 

Bill Boehme

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Bill, why do you think what I'm doing is not more widely used by woodturners? I know its easier to leave things on a shelve for 6 months, but for box making I believe its going to help me a lot... Also, some of the wood I got in exchange was kiln dry. Boy!! Nastiest driest wood ever, cocobolo, made a mess too, orange dust all over... The box I did today was from an old Kiawe fence post, cut over 20 years ago, dried naturally, my chasers were making beautiful tiny shavings, a beautiful sight that gives this grown man goosebumps haha. Did I tell you the oven light is working perfectly!! Best tip yet so far out of this thread!! The 40 watts is just right!! Aloha from Maui.

Well, Trent Bosch, Kelly Dunn, Dale Bonertz, and probably you are production turners/professionals/turners who do it as a business. Other professionals have a full pipeline by using simpler methods like Anchorseal and sit on a shelf or bagging.

For me, drying three or four pieces in a kiln doesn't make sense. If I'm not mistaken, you have to turn a bunch of rough outs load up the kiln and then don't mess with it until you unload the whole batch. In other words, you can't have pieces at all stages of drying ... Everything is at the same stage, just like a lumber drying kiln.

My current method works for me. I'm familiar with the local problem woods (post oak, fruit wood, and juniper) and generally don't mess with them. I probably have a couple years worth of wood on hand that is already dry. Your climate is much more humid and not as hot as Texas so a kiln might be the right answer. My favorite wood is mesquite which doesn't need to be dried. It is one of the most stable woods there is.

I also turn a lot of figured maple. You don't find much maple here so I buy maple blanks. Some of it is wet, but by the time that I get around to them, they will have dried. I haven't been able to turn for almost a year, but I keep buying maple blanks and probably have accumulated forty or fifty. :D

Anyway, I think that non professional turners don't create enough volume to make a kiln practical. I think that somebody like @dbonertz could give you a more definitive answer.
 

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Bill, why do you think what I'm doing is not more widely used by woodturners? I know its easier to leave things on a shelve for 6 months, but for box making I believe its going to help me a lot... .
Many production turners use kilns.
Kilns tend to work best with a near full load 40 - 300 bowls depending on the size.
Kilns take up a good bit of space,

People turning a few bowls a week don't generate the volume of bowls to fill a kiln and the benifit of kiln may not justify the space.

Production turners on the other hand save space by reducing the storage needed for bowl drying to the size of the kiln. Also from an economic perspective they are shortening the production cycle considerably and ruducing inventory of bowls not ready for market.

I have no interest in a using a kiln I only finish about 6 twice turned bowls last year.
I do mostly hollow forms & NE bowls. These dry in a day or two with little attention and no need for a kiln.
 
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"Bill, why do you think what I'm doing is not more widely used by woodturners?"

How do know the percentage of turners that are using kilns? Quite a few guys in my club are.
 

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How do know the percentage of turners that are using kilns? Quite a few guys in my club are.

The dearth of published design information about kilns is an indicator that they aren't widely used. What plays in Peoria might not be the optimal approach in a different climate. I belong to a very large club of 200+ members and nobody uses a kiln. As Al pointed out it might make sense for production bowl turners, but not for somebody who turns a few bowls a month. We don't have any production turners in our club other than a spindle turner.

Before rushing off to build a drying kiln, here is some good information from a commercial operation on drying hardwood lumber.
 
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About a dozen years ago when Trent Bosch was teaching classes at our club he did a presentation on the kiln that he used for drying bowls. From your description, your kiln sounds very similar.

It is. I know Trent and actually used his old kilns for many years. I built mine based on his.
 

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"Bill, why do you think what I'm doing is not more widely used by woodturners?"

How do know the percentage of turners that are using kilns? Quite a few guys in my club are.
I guess they dont bother to help a fellow kiln user. Thats what I'm guessing my estimate, how few have bother to answer. I guess not everyone reads this forums...I know I'm the only one out of 32 club members in Maui.
 

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Many production turners use kilns.
Kilns tend to work best with a near full load 40 - 300 bowls depending on the size.
Kilns take up a good bit of space,

People turning a few bowls a week don't generate the volume of bowls to fill a kiln and the benifit of kiln may not justify the space.

Production turners on the other hand save space by reducing the storage needed for bowl drying to the size of the kiln. Also from an economic perspective they are shortening the production cycle considerably and ruducing inventory of bowls not ready for market.

I have no interest in a using a kiln I only finish about 6 twice turned bowls last year.
I do mostly hollow forms & NE bowls. These dry in a day or two with little attention and no need for a kiln.
When I'm in a rush, or the client is in a rush, I usually suggest a NE bowl. Lots of clients come to the studio, they tell me I have an anniversary, what do you have, I then ask: when is it? Tomorrow!! LOl My Kiln is tiny.... A small flower case, looks just like a coca cola glass door refrigerator by the checkout line at all supermarkets...
 

Emiliano Achaval

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The dearth of published design information about kilns is an indicator that they aren't widely used. What plays in Peoria might not be the optimal approach in a different climate. I belong to a very large club of 200+ members and nobody uses a kiln. As Al pointed out it might make sense for production bowl turners, but not for somebody who turns a few bowls a month. We don't have any production turners in our club other than a spindle turner.

Before rushing off to build a drying kiln, here is some good information from a commercial operation on drying hardwood lumber.
What a good article! Man, I'm in way over my head, lol. Its a good thing I have more wood than a few production turners will use in a few lifetimes! I can manage to ruin a few pieces with trial and error...
 

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I guess they dont bother to help a fellow kiln user. Thats what I'm guessing my estimate, how few have bother to answer. I guess not everyone reads this forums...I know I'm the only one out of 32 club members in Maui.

Emiliano......You really should try and make contact with Kelly Dunn. I'm surprised you're the only one in your club using a kiln there in Maui. If I'm not mistaken, I believe he said the woods there in the islands never do get below a certain MC, and I don't recall what that number was, but it was above what is needed for successful turning......especially if the piece ended up in a dryer climate. Seems like you'd use a kiln there out of necessity, rather than convenience.

I just ran a search on these forums for Kelly Dunn, and came up empty handed. That seems strange, because he was a regular contributor to these forums, a year or so ago......:confused:......Kelly was very free with his advice and knowledge, so I'm sure he'd be happy to help you out in any way he can.:cool:

I've been following this thread out of curiosity, and I've never used a kiln. For me, it's simply a matter of having a quantity of roughed bowls in the process of drying at any one time. I don't run out of work to do. I don't know what is considered a "production turner", but my current rate of production is about 6 +/- bowls per month. I could easily step up that rate, but don't sell at that rate, so I'm in no hurry to produce faster.......:D.......I'm good with this, because I'm retired, and do not ever want to feel "rushed" again! ;)

ko
 
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This is a good conversation on kilns. One thing I noticed in the kiln drying article was a lack of discussion of drying temperature. I've always steered clear of building a heated kiln, opting for the dehumidifier in a closed room version. I'll give some of my reservations—just for the sake of being aware of them for those who do use kilns.

Working in shipyards in my 20s and 30s, I was around a lot of very talented old-school shipwrights, and I've yet to ever meet a shipwright who has anything good to say about kiln dried wood. Granted, a marine environment is VERY different from that of a home. Here's the shipwights' objection. In heating wood (I think the temperature cut-off is around 120+) the natural enzymes are killed. As with boiling wood, if kiln drying is done too fast, the cell walls also rupture. In a marine environment, kiln dried wood rots very quickly, probably due to the loss of natural enzymes that keeps wood still "alive"—so to speak. I've seen beautiful work come back into the shipyard rotten for no reason other than kiln drying of the wood. At the extreme end of heat, amazing doug fir came out of the 1980 Mt. St. Helens eruption, and a lot of the working fleet had repairs that came back a few years later with all of the new replaced planking rotting.

I've ordered kiln dried lumber from a number of different mills, and while the quality control may have been so-so in some of the more local mills, I swear I can feel a difference in how the wood cuts, especially with handtools. I've heard the same from a number of furniture makers. My take away for us woodturners is that I'd want to try air-dried versus (heat) kiln dried. I suspect that air dried may cut cleaner on the lathe, too.

I've also seen some issues where the kiln dried wood was supposedly dry, but wasn't. When I built a house for my parents, 1500 sq feet of flooring arrived, and after letting the wood acclimatize, I began installing the floor. Then the funny stuff started... After about ten rows of 3 1/8" flooring, my distance started growing on one end of the floor. What I eventually determined was that the flooring had almost been dried fully, but not quite. Every piece of flooring was a little less than 1/64" wider on one end. The sawyer died about that time, so we were stuck with the wood. I can only guess that the fan in the kiln was blowing one direction, and the far end didn't quite dry fully before going through the shaper. I ended up having to join the flooring by hand in-place (after it had been nailed down) with a rabbet plane every 2 to 3 feet. The floor turned out great, but it was a heck of a lot of extra work. The take away: if a sawyer of 40 years can have that quality control issue with his commercial kiln, it can happen other places.

Next sad-story: A friend returned from a vacation a few years ago with a beautiful vase and bowl from a professional turner of good reputation, who is well known for drying wood in a kiln. The vase both warped and cracked, and the bowl was more warped than I would call acceptable for a twice-turned bowl. Granted, my friend heats with wood here in Alaska and has a very dry house, but this is still wet, temperate rainforest on this lower edge of Alaska....nothing like desert Arizona.

So: I'm not discounting heated kilns entirely...I'm just saying, keep an eye out for potential problems, especially with too much heat and incomplete drying. I'm confident that closer attention to detail could have prevented both the flooring and turning problems. As for "killing" the wood, I think that is just something to be aware of past 120°F or so. Again, I would want to compare air dried to kiln dried, and maybe even do some experiments with bowls in utility use.
 

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The often repeated old woodworkers tale about cell walls rupturing doesn't hold water (pardon the pun). Most likely it is being confused with what happens when wood becomes case hardened because of kiln drying at too high a temperature or some other wood defect. The article that I previously referenced barely mentioned case hardening and what they said wasn't quite detailed enough to get a complete picture. However, an important point in the article is that the main goal of kiln drying isn't to speed up drying, but to get the wood into a dry stable state by hardening the lignin. Faster drying has to be tempered with understanding drying defects. As the article says, you're walking a fine line between getting a dry stable product and unstable case hardened wood. Case hardening isn't a YES or NO condition because it exists to a certain degree in all kiln dried wood. With proper drying, the effects of case hardening can be kept unnoticeable.

Most woodturners know the difference between "free" and "bound" water, but for the benefits of any new turners who aren't familiar with these terms, here it is. Free water is the water that exists in the cell cavities and in the xylem (the vessels that transport water and nutrients to the to the leaves. During the active growing season roughly 2/3 of the water in wood is free water. When drying roughed out bowls the free water quickly evaporates or slings out during rough turning. After the free water has evaporated the wood begins to shrink as the "bound" water evaporates. "Bound" water can also be called water of hydration because it is water molecules that are attached by weak ionic bonds to the cellulose that makes up the cell walls as well as the lignin and hemicellulose. Bound water evaporates much more slowly because thermal energy is required to separate the ionic bonds.

While drying rough turned bowls and other turnings in a kiln isn't the same as drying lumber there is enough commonality between them that the "Dry Kiln Operators Manual" published by the USDA Forest Products Laboratory is a very useful reference. Here are some select chapters from the book that I think would benefit all turners even if not interested in kiln drying:
  • Introduction, TOC, and Glossary -- Good general information and useful glossary.
  • Chapter 1 Properties of Wood -- This should be a "must read" for all woodturners who want to get a basic understanding of wood.
  • Chapter 3 Auxiliary Equipment -- you can skip or skim through this chapter
  • Chapter 8 Drying Defects -- This chapter is another one that all woodturners ought to read.
  • Chapter 9 Operating a Dry Kiln -- While this is aimed at commercial kilns, there is useful information that can help with designing woodturning kilns.
While many woodturners find drying kilns useful, there are plenty of caveats that I think render them impractical for most woodturners. I also have read about some kiln designs in forums that seem just plain poor designs. However, I think that a rough turned bowl is a lot more tolerant of drying defects than than hardwood lumber would be.
 

Emiliano Achaval

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Emiliano......You really should try and make contact with Kelly Dunn. I'm surprised you're the only one in your club using a kiln there in Maui. If I'm not mistaken, I believe he said the woods there in the islands never do get below a certain MC, and I don't recall what that number was, but it was above what is needed for successful turning......especially if the piece ended up in a dryer climate. Seems like you'd use a kiln there out of necessity, rather than convenience.

I just ran a search on these forums for Kelly Dunn, and came up empty handed. That seems strange, because he was a regular contributor to these forums, a year or so ago......:confused:......Kelly was very free with his advice and knowledge, so I'm sure he'd be happy to help you out in any way he can.:cool:

I've been following this thread out of curiosity, and I've never used a kiln. For me, it's simply a matter of having a quantity of roughed bowls in the process of drying at any one time. I don't run out of work to do. I don't know what is considered a "production turner", but my current rate of production is about 6 +/- bowls per month. I could easily step up that rate, but don't sell at that rate, so I'm in no hurry to produce faster.......:D.......I'm good with this, because I'm retired, and do not ever want to feel "rushed" again! ;)

ko
Kelly writes almost daily on the Wow website. You could print a large book with his writings. He's from the Big Island. I'm on Maui. Bone dry Koa here is 12.4%. I got some good advice from Cindy Drozda. She has a pdf on her home made kiln. Mine is working great!! As I turn green boxes I weigh them, and throw them in. Just sent 23 Koa bowls all over the mainland, hope they like the weather where they are going, Koa is famous for cracking over there... I make at least one bowl or box a day. Sometimes more... Am I a production Turner? Lol
 

Emiliano Achaval

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This is a good conversation on kilns. One thing I noticed in the kiln drying article was a lack of discussion of drying temperature. I've always steered clear of building a heated kiln, opting for the dehumidifier in a closed room version. I'll give some of my reservations—just for the sake of being aware of them for those who do use kilns.

Working in shipyards in my 20s and 30s, I was around a lot of very talented old-school shipwrights, and I've yet to ever meet a shipwright who has anything good to say about kiln dried wood. Granted, a marine environment is VERY different from that of a home. Here's the shipwights' objection. In heating wood (I think the temperature cut-off is around 120+) the natural enzymes are killed. As with boiling wood, if kiln drying is done too fast, the cell walls also rupture. In a marine environment, kiln dried wood rots very quickly, probably due to the loss of natural enzymes that keeps wood still "alive"—so to speak. I've seen beautiful work come back into the shipyard rotten for no reason other than kiln drying of the wood. At the extreme end of heat, amazing doug fir came out of the 1980 Mt. St. Helens eruption, and a lot of the working fleet had repairs that came back a few years later with all of the new replaced planking rotting.

I've ordered kiln dried lumber from a number of different mills, and while the quality control may have been so-so in some of the more local mills, I swear I can feel a difference in how the wood cuts, especially with handtools. I've heard the same from a number of furniture makers. My take away for us woodturners is that I'd want to try air-dried versus (heat) kiln dried. I suspect that air dried may cut cleaner on the lathe, too.

I've also seen some issues where the kiln dried wood was supposedly dry, but wasn't. When I built a house for my parents, 1500 sq feet of flooring arrived, and after letting the wood acclimatize, I began installing the floor. Then the funny stuff started... After about ten rows of 3 1/8" flooring, my distance started growing on one end of the floor. What I eventually determined was that the flooring had almost been dried fully, but not quite. Every piece of flooring was a little less than 1/64" wider on one end. The sawyer died about that time, so we were stuck with the wood. I can only guess that the fan in the kiln was blowing one direction, and the far end didn't quite dry fully before going through the shaper. I ended up having to join the flooring by hand in-place (after it had been nailed down) with a rabbet plane every 2 to 3 feet. The floor turned out great, but it was a heck of a lot of extra work. The take away: if a sawyer of 40 years can have that quality control issue with his commercial kiln, it can happen other places.

Next sad-story: A friend returned from a vacation a few years ago with a beautiful vase and bowl from a professional turner of good reputation, who is well known for drying wood in a kiln. The vase both warped and cracked, and the bowl was more warped than I would call acceptable for a twice-turned bowl. Granted, my friend heats with wood here in Alaska and has a very dry house, but this is still wet, temperate rainforest on this lower edge of Alaska....nothing like desert Arizona.

So: I'm not discounting heated kilns entirely...I'm just saying, keep an eye out for potential problems, especially with too much heat and incomplete drying. I'm confident that closer attention to detail could have prevented both the flooring and turning problems. As for "killing" the wood, I think that is just something to be aware of past 120°F or so. Again, I would want to compare air dried to kiln dried, and maybe even do some experiments with bowls in utility use.
I too wonder about the temperature. My 40 watt incandescent bulbs keeps the temperature at a steady 85,...
 
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