Wood Drying Kiln Temp?

[Tom Hansen]

I picked up a broken mini fridge, about 12 cu. ft. and rigged up a single bulb inside. Anyone have the definitive answer on what temperature I need to be aiming for to dry out once turned blanks? Is there such a thing as too hot or too cool? Do I need to worry about mechanically evacuating humidity inside periodically or would opening the door a couple times a day suffice? Maybe I want to keep as much humidity inside as possible to avoid cracking? I'm planning on blanks about 1".

I have zero experience with drying in anything other than a paper bag. Is there a thickness that's too thick and would cause cracking problems? Too thin?

Any and all of your experience welcomed.
Thanks in advance for your help.

 

[Karl Loeblein]

Start with a full kiln if possible to keep the moisture up so your turnings don't dry to quickly. Suggest keeping the heat around 100 degrees for the first few days and then slowly raise the temp to 120 degrees as the wood starts to dry out. Also, put a couple of small vents in the top that can be closed off if moisture gets too low. Your goal is to keep the moisture level the same throughout the pieces as much as possible.

 

[Richard Coers]

I start at 90 degrees for several days. I open the door occasionally to release some humidity after experiencing some mold problems with a huge load of red oak bowls. When that happened I washed with diluted household bleach and back to the kiln. Then start slowly going up from there. Speed and heat depends on wood species. Ash and walnut can go pretty fast, fruit woods and white oak, much slower. If the wood had any sign of insects. particularly powder post beetle, I take it to 150 degrees to sterilize the wood.

 

[Dean Center]

Back when Dale Bonertz was making and selling rough turned bowls and drying them in a homemade kiln, he told me that heat wasn't the key ingredient in the process, it was the air movement. I think he only heated up to 80 or 90, at the most, with a very slow start to the process.

 

[Kevin Weir]

Another tool you can use in the drying process is weight. When my drying box has bowls in it, I weigh them once a week, turning the heat up from 90 degrees to about 120 over the course of several weeks. Once the weight stabilizes, additional time in the kiln is of questionable value. A small kitchen scale handles up to 4 kg or about 9 pounds.

I use an old school method of coating any end grain on wet-turned bowls with paste wax. This helps reduce checking and slows the drying, redirecting the moisture loss to face grained areas.

 

[Tom Hansen]

I use an old school method of coating any end grain on wet-turned bowls with paste wax. This helps reduce checking and slows the drying, redirecting the moisture loss to face grained areas.

That was also something I was curious about. I considered anchorseal or even parafin on the end grain. I've lost a lot of wood to cracking so I'm a bit jumpy to say the least. Most was fruit wood but still. Just a light coating of pastewax?

 

[Richard Coers]

If you are doing a lot of thicker fruit wood rough outs in the kiln to double turn, it helps a lot to stay further away from the pith than most other species. Also put a nice big radius on the top edges of the rim. Sharp edges like to start cracking more easily.

 

[Kevin Weir]

That was also something I was curious about. I considered anchorseal or even parafin on the end grain. I've lost a lot of wood to cracking so I'm a bit jumpy to say the least. Most was fruit wood but still. Just a light coating of pastewax?

Hi Tom. Paste wax is cheap and mostly paraffin so I usually apply a heavy coat, not only to end grain but also to crotch and figured areas. Some fruit wood, especially apple, has a high ratio of tangential to radial shrinkage. So it tends to be difficult to dry without checking. In this case, slower wins the race. Many of the apple bowls I turned have air dried for more than a year with very gradual kiln drying. If there’s a step to hurry through, it’s rough turning. The more time a fruit log or plank sits after cutting, the greater the risk of checking.

 

[John Tisdale]

Don't pass go and collect $200 until you read Gene Weingert's white paper: https://www.lignomatusa.com/wp-content/uploads/2015/02/DryingLumber.pdf
It's right up there with Bruce Hoadley's: Understanding Wood

 

[Tom Hansen]

Thanks for the link John. That's a great read.

 

[Tim Tucker]

That is a lot of good info. I add my kudos for you posting that link John. Thank you.

 

[Arthur Crozier]

Hopefully this link works. It is to a PDF of the USDA “Wood Handbook Wood as an Engineering Material”.

It has a chapter on drying wood as well as requirements for shipping wood products internationally.

https://www.fpl.fs.fed.us/documnts/fplgtr/fpl_gtr190.pdf

It covers a few aspects that were not in Bruce Hoadley’s book.

 

[Emiliano Achaval]

100 degrees like someone said above will crack everything within minutes. I have a tall small fridge with double insulated glass doors, used to display flower leis, the collar of flowers you get when you arrive in Hawaii. I have two 1.5 in holes on the bottom and 2 on the top. I can close them and open them as needed. I have a humidity and temperature meter from Amazon inside. I forgot the name of it, mental block. I use a 25 watts incandescent light bulb. Anything bigger than 25w will crack the Koa or anything else I put in there. Instead of 6 months, I can dry one rough turned bowl of box blank in a month or 2 tops. Temperature is usually around mid 80's. Humidity will drop as days go by.

 

[Tom Hansen]

I've been running around 90 and so far so good. Appreciate the input from everyone

 

[Glenn Lefley]

Cindy drozda mentioned at her last remote demo her kiln was at 85 f. When she first set it up and was keeping track of temperature etc.

 

[Perry Hilbert]

I always understood the control of humidity was more important than temperature. A slow even dissipation of humidity is required. A slight heat just helps evaporate/convert moisture to humidity faster. I stack my wood in a pole barn on skids. stacked with air spaces between. pieces to aid circulation. On hot summer days it gets up to 120-130 degrees in there. I get 3.5 x 5 inch pieces of rough sawn poplar and stack it that way in March, it is dry to use by October. I tried the same with red maple branches about 3 ft long. It was not quite dry by October but by the following spring it was. Wood that has been in there for more than two years seems plenty dry.

 

[Mike Johnson]

A slow and steady removal of moisture until you reach the desired moisture content, then increase the temperature for 24 hours to kill the insect larvae, then shut off the heat and let your kiln and wood cool down for another 24 hours. Holding a temperature of 150 degrees for 24 hours will usually kill off all insect larvae.