My kiln build

[Bill Boehme]

What Mike said about reducing volume makes a lot of sense. A volume that is too large for the number of turnings will force the wood to dry out too fast. Think of the primary purpose of your kiln is to prevent cracking rather than speeding up drying.

 

[Dave Mueller]

Mike,
Great chart data... thanks. One question - when you open the door to weigh the pieces, the moisture loss would drastically lower the RH in the box. It would seem that near the end of the drying cycle, there is not much moisture left in the wood to replenish that lost when the door is opened. Is this a problem?

 

[Mike Brazeau]

Thanks Dave. At that stage of the drying process it is not really a problem. By then it is the bound water that is being released. Early on I wondered about that too. I generally try to have pretty much a full load but have done small batches too and turned off the computer fan in my kiln and let convection take over. Did a small batch of apple boards about 4-5" wide x 1" thick and a foot long for a fellow guild member. I stickered them and put a paving brick on them. Was a complete success. He made a staved urn for a neighbour. After my four presentations to local clubs I know of about a dozen kilns being made and have seen a few. All kinds of configurations, some using weather stations with wireless sensor to monitor interior so you do not have to open up. I really feel the high initial humidity for about two weeks is the most important aspect. I have second turned a natural edge bowl after twelve days.

 

[DON FRANK]

My reply is slightly off topic in regards to what has worked well for my bowl kiln. My design mirrors a youtube video and his suggestions have proven to work well for me too. Mine is simply an old dishwasher with the motor removed so I'm just using the cabinet. Once the motor and spinner is removed from the bottom there is a hole . A round trouble light will fit into that hole along with a 40-60w bulb depending on the season. I have a piece of barn tin over that trouble light to diffuse the heat more evenly. I removed the sliding racks and cut all the upright spikes off flush that are used to hold plates upright. This allows me to stack bowls easier in the top and bottom rack. I drilled a hole in the front door and ran a probe thermometer thru the door to monitor the temperature. This kiln is kept in an unheated part of my building that will be somewhere above freezing in the winter. With a 60w bulb the inside temperature will maintain about 85 degrees. Since a dishwasher already has vents in the door to allow steam to release no other vents are cut into the cabinet.
The only secret to success for this bowl kiln is to load it full with green bowls all at one time. I think this has everything to do with maintaining full humidity as the bowls begin to start the drying cycle as others have suggested in the thread. Once I load the cabinet I don't open the door for at least two weeks. There is no fan inside to move the air. I have had great success with this system especially when I take the time to put a coat of anchor seal on the outside of the bowls. My 10% bowls will dry in the 2-3wk range. I have done some as large as 19.5" which have 1.5-1.75" sidewalls.
I plan to add a humidity probe so that I can keep the door closed until they are done. The design is cheap and is certainly not very scientific but it works very will with very little cracking or failures. I plan to experiment with boiling half the bowls and not boiling the other half in the same batch with identical wood and see if I can determine any benefits from taking the time to boil. I would certainly prefer to not take the time to boil but I have seen that it seems to help.

 

[Perry Hilbert]

Not sure what you are using for thermostats. A poultry incubator thermostat is a mechanical switch that works on the principle of heat expanding air in a sealed container. They turn 110 voltage on and off. Adjustable from about 95 degrees to 105 degrees. Years ago, I was hatching hundreds of quail eggs and built an incubator from an old oven. Used two 25 watt bulbs for heat. The incubator thermostat turned the lights off when the 101 degrees was reached. When it cooled, the thermostat container contracted enough to flip the switch and turn the lights on again. Last I bought one, they were about $15.00 Certainly not very sophisticated, but worked.

 

[Dave Mueller]

Thanks, Mike. Good information, guess I'll have to build one.

 

[John Turpin]

Not sure what you are using for thermostats. A poultry incubator thermostat

Well, my Suncourt duct thermostat blew up yesterday. I think I'll try a poultry thermo next time.

 

[Richard Coers]

One caution about loading up a bowl kiln with really wet bowls. MOLD! I filled mine to the gills with wet oak bowls, and everyone of them flashed over with mold in 2 days. I washed them all off with a weak bleach solution and they were fine after that, but loading it full may not be the best method.

 

[Charlie Knighton]

Well, my Suncourt duct thermostat blew up yesterday. I think I'll try a poultry thermo next time.

I have used regular meat thermostat ....I just drilled hole in the dishwasher front and inserted....worked well.....

 

[Perry Hilbert]

A meat thermosat? or meat thermometer? How does it regulate the heat in the kiln?

 

[Charlie Knighton]

Meat thermometer....u regulate temperature with wattage of light bulb and size of hole in bottom of dishwasher......takes some experiment.....I gave up on drying cherry blanks