A kiln dried tenon, an air-dried mortise, no glue and a sloppy fit: wait overnight and the tenon will swell so tight that you can’t budge it. At least that is true where I live – I don’t know what happens in the desert.
How hot does your kiln need to be to dry wood? The answer is not an absolute temperature, but is relative to the temp of the air outside your kiln.
Why? A kiln works by heating air, thereby allowing it to hold more moisture. A 20 degree increase in air temp approximately doubles the moisture the air can hold.
I’m going to dive into some details. You don’t need to know all this. If it seems overwhelming, just set your kiln 40 degrees above the temperature of your shop to dry things and 140 degrees to set bends. Then sit back, drink your coffee and wait for the next blog post.
An example: Say the relative humidly of the air around your kiln is 95% relative humidity. Pretty darn wet! Say you heat that air 40 degrees in your kiln. The air in your kiln will now be 21%, which equates to roughly 4% moisture content in the wood (I.E. the weight of the water in the wood is 4% of the weight of the wood). In my area air-dry is about 12% moisture content; a 5/8″ tenon will swell roughly 1/64″ from 4% to 10% moisture content.
However, 140 degrees seems better than lower temps for setting bends so they don’t deform once they’re removed from the bending form. If I’m setting bends I try and get the kiln to 140 and leave the wood in overnight (assuming the bends have already been air-dried). High heat degrades the strength of wood, so I try not to go over 140 degrees.
Next time: Kiln Heat Sources & Kiln Construction
We had a cancellation from the Continuous Arm Rocker class, October 6-12th, 2016, booked through The Woodwright’s School and taking place in my shop. Visit Roy’s website for more info (the website hasn’t been updated yet to reflect the cancellation).
Plus, I scheduled a 4-Person class in my shop January 22-28th, 2017 on the Continuous Arm Rocker. Visit my website for more info. These classes have been filling up quickly of late!
Stay Tuned: A 3-week class on Velda’s Armchair is in the works at Anderson Ranch in Aspen, CO next September.