microwaving wood?

I have just obtained an old microwave (700Watt and only operates on full power, will take a 380mm diameter object) and will be trying it over the coming weeks.

The advice I have is: Place a cup of water inside the microwave along with the item (protects the magnetron - I believe). Don't try to use anything thicker than 25mm as reports from an experienced user suggest it isn't suitable. Rough turn bowls to a uniform thickness (less than 25mm). Moisten any knots or other sources which may crack during drying with a damp cloth. If you start to see fine checking (cracks) appearing on the surface, STOP as this indicates the wood is now getting too dry. If the wood turns black, you missed seeing the checking and the wood is charring! (Hope that isn't the household microwave you are using) You can use a weighing technique as follows: Weigh the item. Microwave, remove, cool and weigh. microwave again, cool and weigh. Repeat until item seems to stop losing weight (remember to stop if you see fine checking as you are only trying to get down to an equilibrium moisture content, NOT total dryness.

Have fun. This seems to be the ideal way of gett>i just received a bunch of maple and cherry that eventually plan on turning.

Rich, Do a search on Google in this newsgroup under "Microwave" and you'll get reams of anecdotal results. I wouldn't recommend anchorseal and >then< microwaving...you're just defeating the purpose of the microwave by anchorsealing, and you'll also just melt the wax out anyhow.

Quick tips:

-Use low power for short periods of time (20% for 1.5 - 2 mins) and allow to cool for 1/2 hr. between nukings

-If you've got a scale, weigh the wood before nuking and every 3 cycles. Quit nuking when it quits losing weight.

By now the piece in the kitchen oven has long ago been relegated to the scrap pile. Possibly also the piece in the microwave.

What causes cracking is uneven drying ... where the inside dries much slower than the outside. The advice to search the archives for this newsgroup is the best you will ever get as there are several ways to speed up this process with many vocal advocates for each. I nuke pen blanks, boil rough-turned hollow pieces and LDD especially select bark-on wood.

Anchorseal (or other similar-in-function products) are intended for preventing cracks during slow drying. I can't store all of my wood indoors and not all of what I can store indoors will fit in either my boiling pot, my LDD bin, my microwave or my freezer. For everything else, I use Anchorseal type products and stack them neatly outdoors.

Bill

You do not need dried wood to do certain things, and you can dry wood rapidly without degrade outside of the "ovens" as well.

Though I'm getting "page currently unavailable" messages now, you can learn about wood structure and drying by looking at the publications at

One piece of folklore needs to be set to rest entirely before you begin, that being the "inch per year" rule of thumb for drying boards. Face-grain bowls expose almost entirely end grain, with no part more than an inch from the air, and end grain dries at ten times the rate of face grain - thus the checks in a poorly controlled drying situation. If you can dry a board in a year, you can dry a bowl in a month; less if you disregard another rule of thumb, the 10% "rule. The 10% rule says to leave the wall thickness at 10% of the diameter to assure yourself a circular piece. It's generally overkill on domestic woods. If you look at those FPL publications, you'll see shrinkage as a percentage across the grain - Tangential - and from center to surface - Radial. Say you have a 10 inch bowl of hard maple which shrinks 9% tangentially (not looking it up, likely less), and you want to get 1/4" thick walls on your bowl. Sound like the 10% rule? Shrinkage is more or less symmetrical ! You'll lost 9% of the total width in worst case, so that's an inch, then your thickness, an additional 1/2 inch, gives you a

3/4" thick wall to start. It will be more than enough, because the drying loss is a combination of the two, T&R, and the Radial is usually less. Depending on the slope of the sides, could be much less.

Now you need to think of that Fiber Saturation Point - FSP - which is around

30% moisture by weight. Anything above that is unbound water, which you can spin out centrifugally on the lathe without any degrade, because degrade happens only with loss of bound water. So spin it fast, throw and let the surface dry, then, depending on the relative humidity, protect from degrade with a newsprint tent or paper bag, or just leave it in quiet air somewhere where its water and surrounding pieces will provide a damp microclimate.

If you like to weigh them, and a postal or diet scale should be good enough, weigh them the first day the surface is dry, and turn them after they've lost about 25% by weight. Or, as I prefer, look at the drop on the rim and the shrinkage across, turn when it's as predicted. Some say give 'em a kiss, and if they're not cool to your lips, turn 'em.

I take my firewood, which is around 20% I would guess, rough it 1/3 thinner than the predicted (it is drier), and set it out for two weeks. Works great, and has enough fudge factor built in to be safe in shape and moisture.

i sure wish i had been storing more anchor sealed wood

Start now. We'll revisit the thread again in a couple of years / couple of tons from now. ;-)

Bill