Microwave oven to dry wood: sharing experience

[patmurris]

I know some do it routinely, and others would rather be dead then being known for doing it... What is your experience with drying pen blanks in the microwave oven?

I've been occasionally drying some blanks that way and for light timbers it does work rather well, but not always. Some timbers will peacefully dry and shrink a little, others will bend a lot, or shrink a lot, of develop checks or even split and sometime all of the above.

Here is how i do it:

1. i weight the wood i intend to dry and write that down
2. i place the blanks on two wooden bbq sticks so that air can flow under them
3. i use short full power bursts until they feel hot but not too much - i should be able to handle them without burning my fingers
4. i leave the door open for 5-10min and heat them again so that they are always about the same temperature - i repeat this a number of times
5. once in a while i weight them again to have an idea of how much water they have lost
7. i go back to step 4 until they stop losing weight

Notes:

How long is a 'burst' depends on how much wood i'm drying. For one blank it may be just 10secs, but for a dozen blanks it may be a full minute.

I always check the wood temperature with my bare hand. With a bit of experience you can also tell whether the wood is still losing water - the heat feels humid at first then it progressively feels drier.

One hint is condensation on the glass plate below the blanks. Each time i weight the blanks, i wipe it off so that the plate is dry. After a while the condensation stops, which does not mean the wood is dry, but tells you it is on it's way.

Drying a dozen blanks can take hours... and is somewhat tedious since i have to start again the MW every 5 or 10 minutes, check the blanks, weight them, start again... until i decide they are dry enough. However, with a little patience i can manage to get fairly dry blanks over the week end for instance. To be safe i'd rather let them sit in a ventilated place for a couple weeks before using them.

 

[glycerine]

I've heard of doing it, but never have. Thanks for the detailed notes.

 

[Justturnin]

I dont hve a shop Microwave...yet. I see nothing wrong w/ the method. I use my Toaster oven and set it about 130 for many many hours. I think a microwave would save me some money on electricity.

 

[BSea]

You can also check the dryness (somewhat) by wrapping the blanks on a paper towel. If the wood is really wet, it's obvious. And as Pat said, the wood will "FEEL" humid at 1st.

 

[lorbay]

On sizes of wood that I can fit in my M/Wave (12 – 14" Dia), I place in a heavy paper bag. This absorbs all of the moisture I check the moisture content before I start. Heat 1st time 3 - 4 min on Hi but getting pretty hot, remove from paper bag and sit it in a cool place till cold. Check moisture and repeat over. I do this till the content is down to 6 or 7%. Then I go turn it. So far have had no cracks, but micro waving wood definitely does something to the wood.

Lin.

 

[ctubbs]

Using the microwave process, DO NOT WALK AWAY LEAVING IT RUNNING! DAMHIT either! For safety purposes, I have a converted charcoal grill where I place a 100W light bulb in the bottom, cross stack the blanks on the grill surface and run the bulb. There are 'control' blanks marked and weighed that get weighed each day. When the quit loosing weight 2 days in a row, the blanks are dry enough. Much safer than forgetting the wood in the MW and catching the LOML's MW on fire. OOPS, now you know why I spoke about forgetting the MW was running!
Charles

 

[MrWizard]

I like the grill idea CTUBBS, safe and its not keeping me from doing other stuff.

 

[leehljp]

I learned early on to cut green wood over size because some woods shrink considerably, some twist and some curl during the drying process. I cut some nice looking blanks to 3/4 in and watched them shrink to 5/8, twist or curl and become useless. Then I tried it with 1 to 1 1/8 inch sizes. Took a few minutes longer but even with a twist or curl, there was usually enough material for a straight bore and great pen.

Another thing I learned is that you DON'T cook too long at a time. Try it with a corn cob and see what I mean!

 

[toyotaman]

I've got a microwave,toaster oven, and a small crock pot in the shop. The crock pot has wax in it and it comes in handy when I need to seal up some pen blanks. I put my blanks I want dry in the microwave for 1 min. Then take it out and let it cool. Repeat this process and after a few cycles I start checking the blank with a moisture meter until dry. It doesn't take long.

 

[joeatact]

I have had good success using the microwave to dry wood. I use the defrost cycle a little safer and doesnt burn the wood. But always beware its can start fires

 

[WillieD]

I've never dried pen blanks in the microwave, but do dry both box and bowl blanks.

1. Seal the end grain with thin CA and put them in a zip-lock style bag and leave them sealed until each cycle cools completely.
2. Use multiple short cycles (15 to 30 seconds based on amount wood) and pause after each cycle to allow the heat to evenly distribute through the entire blank.
3. After complete cooling, use a paper towel to dry the inside of the bag and the blank.
4. Reweigh the blank and stop when the amount of moisture in the bag and weight loss decrease by about half.

How hot I let the blank get in step 2 depends on wood density. For some species I go until the blank is almost too hot to hold against my cheek (Ebonies and less stable species). For some, I go until I can hear the water sizzle in the blank (Bloodwood and some of the more stable Rosewoods).

This method keeps the humidity high around the wood and reduces the number of cracks by about 80% (in my experience).

NEVER walk away from the oven or allow your attention to wander.

 

[leehljp]

Willie and Joe both have excellent suggestions IMHO. I haven't tried either yet but will in the future. Thanks for sharing these!


Believe it or not, LOML and I are still on our second microwave, purchased in 1984 when MWs had only one setting - full on, plus the timer. This microwave went from use in the US to Japan where we used daily (26 years) to back here and in use now. (Our first MW was purchased in 1972 and died in 84.)

Joe, as to the defrost cycle, I have to take your word for it. Sounds logical. I have a small MW with a defrost cycle on it, and it is in storage from our youngest daughter's college days. I may get it out of storage for the shop!

Willie, I like what you said about the crack reducing. Got to remember that.