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Freezer Kiln Temperatures?

T

Ted Mellin

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Apr 4, 2010
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Have recently converted an old freezer into a bowl drying kiln. Have added a light and a thermostat to control the temperatures. Can control the temperature by putting a larger wattage bulb. With a 40 watt bulb the temperature stabilizes at about 90 degrees F. With a 100 watt bulb the temperature goes to about 130 degrees F. Have been told to start at the low temps and progressively go up.

So I guess my question is what temp. should I start with and what temp. should I max. out at? Anybody that has had experience with this I would appreciate hearing from.

thanks - Ted
 
What about Air Flow?

Hello Ted, I think you're on the right path with low temps first, moving to higher temps.

I was wondering if you have any air flow in the "kiln"?
 
It's not the heat, it's the humidity.

Heat allows the warmer air to hold more absolute moisture, which is important early in the dry cycle when the wood's losing unbound water. Of course you have to exhaust all that warm moist air or everything stops drying. So keep the circulation up - heat too, if you care to - for the first few days, then slow it to allow slow migration from the interior to the exterior of the wood.

After a certain point - defined as the fiber saturation point - warming adds energy to help break the hydrogen bonds and release the bound water. You'll notice it when the same interval between humidity readings produces less difference.

So get a hygrometer and a logbook and experiment/document with your schedule. But control the ventilation in preference to the temperature.

Or just say the heck with it and pitch 'em into a sheltered cool corner for a week or two then put 'em on the shelf for a couple months. They'll be fine.
 
Freezer Info

Yes, I have drilled 16 holes, 1/2 inch in diameter in the freezer for ventilation.
Eight of the holes are in the bottom and four more on each side at the top.

The freezer is in my basement where the temperature is always in the low
60's year round. I live in Colorado where the humidity must rank amongst the lowest on planet earth.
 
Trent Bosch also lives in Colorado, but his set up includes a dehumidifier to allow the humidity to be controlled. His box does not include ventilation holes and I am not so sure that they would be very effective. He did a week long program at our club a few years ago and showed us his design for anyone interested in doing the same. Unless you are a production turner, it is hardly necessary. Do as MM suggests. You might contact Trent to see if he would send you a drawing showing his design. His box is rather large, but could be scaled down I suspect.
 
Here is what I do with dishwashers.This isn't very scientific or technical, but it might give you some ideas on where to start. I have no idea how it will relate to a larger freezer.

I like the dishwahers because they vent without having to drill holes or add a fan; and there is no insullation to contend with. Two of them have about the same capacity as an upright freezer or reefer, and I lay a door on top of them for a work table.

I measure the moisture by recording weight loss on a digital scale, but an educated guess is close enough after a few bowls. A pan of water that is the same depth as the thickness of the wood is a good indicator - the bowl is dry when the water in the pan has evaporated.

I measure temperature with a dial thermometer stuck through an 1/8" hole drilled through the door.

I can keep the temperature inside the box at about 95ºF with a 100-watt light bulb, and lower the wattage to 75 or 60 if it exceeds 100ºF when the wood starts to dry.

A single bowl that has been finish-turned to 3/8" wall thickness will stabilize to around 10% moisture content in about 3 days, depending on the species, and the original moisture content. Thicker wood or a full 'dryer' will require a longer time.

For a slower drying rate, I either fill the bowl with wet shavings, wrap the piece in a paper grocery bag, place a pan of water in the bottom of the box, or do all three. The objective is to raise the humidity inside the box and slow the evaporation rate from the wood surface.

Cracking and distortion is reduced because there is less chance of the surface getting too dry and cracking, and is no more of a problem than with air-drying with the bowl inside of a paper grocery sack.
 
Last edited:
why not placed them in a car that is not driven and let the sun dry them for you--- this works better if the car are painted black
 
ray hampton said:
why not placed them in a car that is not driven and let the sun dry them for you--- this works better if the car are painted black
Click to expand...

The object of this method is to control the drying rate so that cracking is minimized -- it is not intended to be a method to accelerate drying to any great extent.
 
Kiln

Ray...Please refer to my blurb in the "how-to and tips" forum on how to make a kiln.... and if you need further info, contact me at woodward@spiritone.com and I will help. If you want simple, easy, cheap that's me!! And above all, it has very good results. I have been using this for about 10 years now, and am using the same heater. I also use it for drying between finishing coats, thus insuring a dust-free place. :cool2::cool2:
 
I have a "Freezer" kiln that I've been using now for a couple of years. I got my directions from Kelly Dunn, a woodturner from Hawaii. His instructions are listed below. He's been using this set-up for over 20 years. First of all, there are many types of kilns. The principles are the same no matter what they are. In this style, cheap and effective, no fans are needed and vent holes are drilled in a grid pattern on the top and bottom. Fans are not needed because hot air rises, it's elementary. The light bulb, which is placed in the bottom, heats the air-the air rises and exits through the top. The air movement will pull "fresh" air in from the bottom, it's heated and exits through the top. Constant air flow. Mine is in my basement. I'll start with a 40 watt, then 60, and finish with 75. I rarely reach 90 degrees by measuring at the top of an up right freezer. I've never needed more than one 75 watt bulb and will dry out a load of roughed out bowls in 4 to 5 weeks. I know some people set there's up with as much as two 100 watt bulbs. There's not right way or wrong way. The key is to find "balance". The holes drilled in the top and bottom, I think, are more important then the wattage. If you have too many you can't keep the humidity. If you don't have enough you can't get rid of it. Kilns work the best when they're rather full. When they half full or less I'll put a pan of water in it to start. When I start a load of bowls and I open the door the first couple of times I'm blasted with a burst of humidity. If you shock the wood with a lot of heat and no humidity I don't care what you do-they'll crack. As the bowls dry the humidity drops. I do have a dehumidifier the basement as well that removes some of the humidity from the air gradually. I'll use this system for my twice-turned bowls. All of my other finish turned-green work I use a box to moderate the air flow to it.

Any other questions please feel free to ask.

Here's Kelly's Instructions.

Refigerator kiln,
Get an old fridge or standing freezer. Free for the taking at landfill
dropoffs and applience repair shops.
Take out all things not needed. On the fridge cut out or take out the
divider section between the fridge and freezer compartments.
Drill some half inch holes in the top and bottom roughly four inches
apart. Get an outlet box and a ceramic lightbulb holder. Put that in
the bottom center. If the plug in wire for the fridge is still good
you can use that. Make a metal cowling to go over the light bulb. This
is just in case so nothing can fall and break the bulb and cause a
spark. Often aluminum was taken out of the inbetween section that is
perfect for a cowling.
The shelving, use ones from fridges and freezers that fit your
unit,can be started right above the light.
Rough turn your pieces to about an inch thick.
Bowls must be coated on the outside with green wood sealer to prevent
from cracking.Pen blanks and small items up to you.
Stack on the bowl sides leaving a very small space for air to travel
in the bowl. And fill the thing up. If you are not in a hurry a 40
watt light bulb can be used and as pieces dry pull them out and rotate
work from the top of the kiln to the bottom. No fan is needed with
this kiln. An air convection current will be created and will work for
you 24/7.
You will need a moisture meter. Even a cheap one will work for this.
Start with a 40 watt bulb. When the bowls are around 14 to 16 %
moisture pop in a 60 watt bulb. With the 40 watt bulb moisture will
drip from this thing. You can leave it or wipe it dry. That will all
be gone by the time you put in your 60 watt bulb. which should four
weeks or under for sopping wet bowls. In about a week the bowls should
be about 12% or less. Pop in a 75 watt bulb. It should be under a week
and the work will be 6 to 8%.If your kiln is in a cold area you may to
go up a 100 watt bulb to do the job. Turn it off and let it cool down
before removing the bowls. If a sixty or 75 watt bulb burns out before
the load is finished and the bowls are cold start with the 40 watt for
a day then move it back up one day at a time to not shock the wood.
When loading the kiln put your most stable woods the closest to the
heat. the bowls near the light will be finished before the ones near
the top are.If you want to pull out hot finished work from the bottom
wrap them in a towel so they cool slower.
This draft written 10-12-2008 and will be upgraded as needed.
I have been using these kilns for 20 years now.
 
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