Knowledge You Can Build On — Est. 1998
question: wood stress
Jim D. Clayton, NJ
>I used the microwave method of drying for the first time this weekend. It was on a small bowl and it really "warped" out of round, much more than I expected. This is not to say it would not have done the same drying any other way, it has a lot of swirl to the grain in it.
My question is , does the heat from this method cause it to distort more than other methods? Would love to hear from some that use this method of drying.
Jim D.
Yes
tdaniel
>Heat is used to bend wood. The MW cuases steam to be produced during the drying thus the temp is high enough for "steam bending" to take place. Shorter cycles might help to minimize the problem.
TD
Re: question: wood stress
John Lucas
>Jim
I've heard both. I just read an article and the guy used the microwave to dry a bunch of bowls and he claimed they had less warp. I've read testimonials on here that claim that you get more warp. My experiences have been that I get about the same as air drying but get more pucker out of curly grain sections.
You can tame the overall tendency to go out of round by clamping the piece over a form. I have a friend who swears by putting a rubber band around the rim. I've never tried that. Virtually all of the bowls I've microwaves are natural edge so I don't even worry about the warp.
Re: question: wood stress
Russ Fairfield
>If the wood is soft enough to move while it is hot, you can put a band-cloamp around it and keep it in shape. Having a somewhat flexible bowl usually means turning to final thickness before drying, not after.
Re: Nuking Protocol (LONG)
Doug Trembath
>Jim, I have at times in the past adapted and combined a couple of techniques to combat this phenomenon, and while it isn't a magic bullet or anything, I have had some success. In prepping blanks, it is good to boil some problem woods, which seems to release the lignin bond significantly, resulting in lessened stress, and consequent movement. I have used this technique very succesfully for Madrone burl, which is highly unstable.
Marrying this concept to the microwave drying works like this. I put the object in a Zip-Loc bag, with a few drops of extra water, remove as much of the air as possible, and nuke it slowly, at reduced power. As it gets hot, the bag will expand, and even "pop" the seal. I stop the microwave, reseal the bag, and do it again, and again, until the wood has been really hot for quite a while, then wrap it in some kind of insulation-like material, and let it "steep", for lack of a better word.
This approximates the 'one-hour-per-inch' rule that Steven Russel developed for his boiling protocol. I then let the piece dry without the bag, and have had some dry with remarkably little distortion. It isn't fool-proof, but I have had it work well. Like everything else, YMMV.
I caution anyone doing this that you need to carefully monitor the amount of moisture, as one of my early attempts resulted in lots of smoke and fire, and a new microwave for SWMBO. Buckeye burl smoke STINKS! It sticks around for quite a while, as well. DAMHIKT!
Doug Trembath
Studio in the Woods
