# Microwave drying of pen blanks



## DCBluesman (Sep 19, 2004)

Please note that these are my methods and results.  I can't guarantee yours.

After reading a number of posts regarding drying of green blanks, I decided to give it a try using a microwave.  I know this is done on a large scale by some lumber companies and figured that there had to be an application for blanks.

First things first...my *setup*.

* 600 watt microwave oven with carousel
* 3/4" x 3/4" x 6" blanks in apple, maple, elm, and ash
* Bounty paper towels
* Borrowed wood moisture meter

Given the fact that I've heard that green wood takes a year per inch to dry, I knew that we needed a significant improvement or the method would not be worth the effort.  My goal was 1 week or less.

*The process*

I started with the blanks described above as provided by a friend who cut these green pieces from a nearby construction site.  None of the wood was more than 4 weeks after being cut/downed.  The wood was noticeable cold and moist to the touch.

I labeled each piece and face...i.e. apple 1, apple 2...

To start with, I placed blanks on a sheet of Bounty paper towel on the carousel inside the microwave.  I was careful to leave space between the pieces so as not to create hot spots.  All blanks were turned at a 45% angle to the wall of the microwave.  I started with side 1 facing up for all pieces.

Recognizing that boiling the wood would damage the grain, I chose to use the defrost power setting (30 percent for ovens that do not have a defrost option).  I treated the blanks for 1 minute, then removed the blanks from the oven and wiped them down with another paper towel.  Then, each piece was laid out on several layers of paper towel such that the evaporation would occur uninhibited.  Blanks were allowed to cool at room temperature for at least one hour such that the core temperature would return to room temperature.  (This was a guess.)

I rotated the blanks 90 degrees to side 2 and repeated the treatment, 1 minute at defrost or 30 percent power.  Again I wiped the blanks down and allowed them to cool on paper towels for at least one hour.  I repeated this process on sides three and four.  At that point, I consider one application of heat to be complete. After a complete application, I waited 24 hours to start the second. 

For these particular blanks, a total of four applications (16 oven cycles) was required to reduce the moisture content to 8-12%...each blank was a bit different.  At that point, based on my understanding of furniture making, I decided that the blanks were sufficiently dry.  Anything under 7% is too dry, producing a brittle wood with significant probability of cracking.  Additionally, at that point, the wood will begin reabsorbing water from the atmosphere.

*The results*

The wood turning feels exactly like professionally dried blanks from the major distributors.  

This sounds like a lot of work, but mostly it is a lot of waiting.  Fortunately, since each microwave full of blanks is only in the oven for 1 minute at a time, you can do a bunch of pieces and have them all complete and ready for turning in less than a week.

*Learnings*

- Do not increase the power or increase the length of time microwaving the wood.  It WILL burn (you can smell it, even if you can't see it).

- When the wood comes out of the microwave, it should feel warm but not hot.  You can always add a dry cycle.  You can't reclaim burnt wood.

- If the wood is sizzling, stop the microwave immediately.  Then restart with lower power, time or both.  Sizzle indicates boil.  Boil is bad.

- Be very careful with spalted wood.  It seems the spalts can burn at a lower tempurature than unspalted wood.  The same appears to be true of knots.

- Smell your wood.  If it smells like it's burning, it probably is.  Wood that is burning on the inside will continue to burn.  Put the piece in a fireproof container or thoroughly cover it with water for at least 15 minutes.  Our finishing compounds have plenty of danger by themselves without adding wood that is on fire.

- Start with small batches and record your results.  Different woods react differently to this method.

- If you don't have a wood moisture meter (and they are darned expensive), you can still determine when the wood is sufficiently dry by weighing it.  As wood dries, it loses weight.  Weigh the pieces before you start and after each four-step drying cycle.  If the weight loss is less than 3 grams(.1 ounce), you are probably dry enough.

Again, I reiterate, this worked for me.  I took plenty of safety precautions.  For your own sake, please do the same.


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## tipusnr (Sep 19, 2004)

Thaks for the detailed information.


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## William Young (Sep 19, 2004)

Thanks for the info.I may try it on some sumac branches I have cut into 6" lengths. I have hundreds of sumac bushes so if it doesn't work it's no loss.
W.Y.


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## melogic (Sep 19, 2004)

Lou,
Thanks for the info. I have some Box elder that is very green. I may try this.


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## low_48 (Sep 19, 2004)

VERY good information. Just a few days ago I dried some Osage and Osage burl in the microwave. I was alot more agreesive running 2 minute cycles at full power. Sorry, don't know the specs on the microwave. I had about 15 half blanks, 1"x1"x3", on the rotary table. Each time I opened the door the blanks would be sizzling and almost to hot to touch. I would let them rest for at least 45 minutes before the next cycle. I did not measure the moisture level, I just kept running them till they had a sharp sound when tapping them together. REAL SCIENTIFIC!!!!! I've turned 5 pens from these and only had one half blank that was ruined. It was completely filled with honeycomb checking. Looked good from the outside, filled with cracks on the inside.

In no way is this a knock on your method, I think your method is dead on for highly consistant results. I just wanted to share my experience. I've got these blanks out the whazoo and had nothing to loose.


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## Mac In Oak Ridge (Sep 19, 2004)

I have been lusting for a moisture meter.  I got a Harbor Freight catalog a few weeks ago and they have one listed, pin type, for $29.99.  On line the price is $24.95 plus postage and handing.

I just ordered one.  I know Harbor Freight stuff is not high end but I have never gotten anything from them that wasn't fairly described and that didn't function as advertised.  Most recently I bought a 23 gage Pin Nailer from them. It works quite nicely for home woodshop kind of work.  No idea if it would hold up in production. I put 100 23 ga. 1/2" pins through it as fast as I could pull the trigger, as a test.  Not one misfire, not one bent pin, not one jamb.  Good enough for me.

It really doesn't matter for home wood shop work if the thing is accurate to hundredths of a percent.  If it gets in the ball park with readings it is all that most people would need.  The ad says +-1% and that is good enough for me.

Anyone else ever buy one of these?


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