# Microwaving green wood. Fail



## hwebb99 (Nov 27, 2012)

I had this green cherry bowl. It was the smallest core from a much larger bowl. It had screw holes from mounting the larger bowl. So it was no big loss. The outside looked fine but when I finished turning it the inside was burned out. I can't find my moister meter, but it did seem dry when I turned it.






any idea why it happened besides microwaving to long. Is there any way to tell how long to microwave the wood.


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## Bill Boehme (Feb 9, 2014)

Woodturning is not a good hobby for the impatient and it's best not to cook it like you would a casserole.

My best advice is to forget about microwaving. However, barring that, here is my recipe: Begin reading *here **in the Microwaving Wood* thread from several months ago where I describe a sensible approach to microwaving (in other words not the method described in the opening post).


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## hwebb99 (Nov 27, 2012)

I'm done microwaving wood. I'm going to rough out bowls like a mad man for the next year. Then I should have enough air dried wood to keep my from microwaving wood.


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## billrlogan (Feb 15, 2014)

No microwaving


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## Quickstep (Apr 10, 2012)

I successfully nuked a piece of olive wood that was 3" round by 12" long. A subsequent attempt to nuke a different piece of olive wood that was 2" round by 2" long and it cracked all over. I'm inclined to give up nuking, but here's my situation:

I make peppermills and give them away. At my margins, I need to do a lot of volume. Sometimes that means I need to turn one around quickly and I might not be able to get a dry blank. I'd love to find a way to dry a blank without having it crack, so I wish there was a scientific approach to this microwaving thing. I have a beautiful piece of bloodwood that I'd like to use for to make a pepermill that looks like a wine bottle. To get it dry, I suspended it over a heating vent that blows warm air that's at 45% RH and rotated it 90 degrees every day. That treatment created scores of surface cracks almost instantly. So, for now I've reverted to patience for drying, but I'd sure love to find another way to speed things up. 

I had this thought. What if.......

What if I:

Drilled the inside of the mill slightly undersize from the final dimensions
Turned the outside slightly oversize. 
Now I'd have a tube of sorts. I 'spect the walls would be 3/4" thick at some locations and as little as 1/4" at others based on the shape of the mill. 
Then, marinate the whole thing in denatured alcohol for a few days, maybe even a week?

After that, would the DNA evaporate quickly leaving me with a low moisture content without causing cracks? Sounds like a long shot, but I figured it was worth asking.


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## hwebb99 (Nov 27, 2012)

I have heard of people using alcohol, but it would be costly. My cherry bowl warped like a potato chip, but didn't crack. My next try is putting wood in this air vent above my fireplace. It maintains about 120F. It isn't used in the house system. There is a fan on it that blows warm air into my shop. I might have better luck on the other end of the vent the air is about 80F coming out.


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## NCPaladin (Aug 7, 2010)

I haven't tried it but in a video on turning green wood by Michael O'Donnell he did on one.
He nuked it for about 1 minute then sat on the counter to cool and let moisture evaporate for a few minutes. IIRC he did this about five or six times so it probably took about an hour total.


Quickstep, I have used DNA and it works fairly well. For a pepper mill I would leave it even thickness, if not the 1/4 will dry before the 3/4. For the rough just leave it all 3/4.
I still coat the endgrain when removed from the DNA for final drying after about an hour when the surface DNA has evaporated.

Hwebb99, the vent may work but typically you want to slow the drying and almost stop air movement (normally in a paper bag). Give it a shot and let us know.


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## hwebb99 (Nov 27, 2012)

I have about 50 bowl blank corners. That I cut off the bowl blanks. I am going to burn them anyway, but I will try to dry them first. If they crack I'll know that idea won't work


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## DonAlexander (Apr 12, 2012)

NCPaladin has most of the right idea. I've microwaved a lot of wood over the past 6 months, in part to see what I could learn and in part to see if some of the experts here were right or not that you can't hurry wood drying. I've done a lot worse than you in terms of burning wood before I started to slow down. The essence of what I learned is you CAN dry smaller pieces of wood in the microwave up to about the size of a pepper mill blank (maybe larger but I can't say for sure). Something the size of pepper mill blank usually took me 3 days and 6 or 7 MW attempts to get dry. I always started on a low setting (30 or 40% power - 40% was the max I could use). I heated the wood until I got a surface temperature that averaged 150 deg. F. and was under 180 deg. F everywhere. If you hear hissing, you've over done it and need to back up. Depending on the size of the wood and the initial moisture content 2.5 to 4 minutes @ 40% was normally enough to accomplish this. For a pen blank, a minute might do it. I let the wood cool to room temperature before reheating. This was primarily to let the warm moisture vapor escape and re-equalize internally. I learned not to hurry reheating the wood and usually did just 2 or 3 heatings per day.

The difficult question for me was figuring out when I was done drying the wood. I always weighed the wood before heating, after heating, and after cooling. The weight decreased after heating and after cooling until the wood was really dry. This gave me something of a curve and let me estimate when I might be down to 10% MC (after making some assumptions about how wet the wood was to start). I also used a moisture meter (one I paid about $25 for at Lowes). It was pretty consistent reading any spot or area but I found the moisture content isn't uniform in a piece of wood - especially if there's sap wood and heart wood but end grain and side grain will give very different readings. 

As the wood dried after going through successive MW cycles, the weight drop became less and less. The time and power settings also needed to be dropped. If I used 4 minutes at 40% power initially, by the third cycle I was at or exceeding my 150 avg temp or my 180 max temp. I'd back up either time or power or both to keep my temps in range. I measure these in several areas with an IR remote thermometer ($20-30 at lots of stores).

I have tried drying roughed out green bowls with mixed success using this method. Some of my bowls, oak in particular, got really hard. What were easy cuts with the green wood were no longer possible. Turning a bowl was much slower going. At first I thought I may have over dried the roughed out bowls. After trying some kiln dried oak bowl blanks, I'm not so sure. Dried oak is hard and smaller cuts seem to be the order of the day. Maybe i need to learn to sharpen my tools better, too. 

The problem I see with microwaving larger pieces of wood is getting the moisture out of the center efficiently. I have real questions about whether the MW can do this even moderately efficiently in an 8-10 block of wood 4-6 inches thick. If you read up on how wood dries, I think you'll discover my concern.

In short, I no longer look for 10% m.c. in stuff the size I'm drying (pepper mill and smaller). Based on Bill Boehme's comments, I think if you get the m.c. under 15% turning the part on the lathe will do the rest.

That's my .02 worth.

Don


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## 9thousandfeet (Dec 28, 2014)

Anytime green wood is placed in an environment where moisture evaporates_ from_ the surface faster than it can be transported _to_ the surface from deeper in the wood, stresses from uneven shrinkage rates occur.
Some woods have faster internal moisture transport rates than others. Generally speaking, the faster moisture transports within a particular wood, the less troublesome that wood is to dry. But not always, depending on the wood's elasticity, and that not only varies by species, but can also vary from tree to tree within a single species.
Some woods are elastic enough to absorb these stresses and some are not. When they are, the wood will just warp. When they are not, it will crack as a result of warping.

Are there ways to "speed up" drying without the cracking? Oh sure.
Do all these ways involve extra time investment and in many cases extra financial expenditure and extra space? Yes, they do.
Is there one single strategy that will work for all species of wood, in any thickness? No, there is not.

Are all these various strategies a big pain in the neck and not near so much fun as turning? You bet.

Which is why I spend a couple of months every year (winter is best, like right around now) replenishing the larder by turning nothing but green wood to make rough-turned blanks and prepping spindle-oriented stock for peppermills or whatever.
That way I only have to be patient one time, for the first year or so, then so long as I re-stock the larder every year, I'm never needing to hurry a drying process.

I find that seasonal rhythm to the work to be enjoyable; it kinda makes sense to me. 
Whereas diverting my energies into different schemes trying to force the wood into doing something it doesn't want to do makes no sense to me at all. But maybe that's just me.


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## NCPaladin (Aug 7, 2010)

Just want to add.... In O'Donnell's video he rough turned the blank to about 3/4-1" thick, then nuked. He didn't microwave the full blank.


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## arvanlaar (Dec 29, 2014)

If you have a fireplace or woodstove, you can generally dry out a rough turned bowl in a few sessions. I bought firewood this year and its pretty green but being inside for a week or so its pretty much as dry as you can get it. 

Also, you can look into building a solar kiln to dry your wood fast on the cheap. There are several ways to dry your wood pretty quickly without microwaving it.


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## hwebb99 (Nov 27, 2012)

The bowl corners have been behind my bandsaw for about a month. They have no cracks. I laid a few on the fireplace hearth. I left them there while I went to church,I was gone about 3 hours. When I got back they had cracked in about 50 places. I think that is just to hot to dry green wood. The house is pretty dry this time a year, just bringing wood in the house should dry it pretty fast.


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