drying wood in oven or microwave

[Alan Carter]

I have some questions about drying wood in an oven or microwave. After rough turning and hollowing with walls around 3/4"-1" thick, what's a ballpark time frame for drying it this way, and at what temperature? Does the species or size of the turning (not the wall thickness) matter? Can you go too long and overcook it?

Jim at Australianburls.com suggested 18-24 hrs at around 170 degrees. Does this seem about right? We have an electric oven so the heat is drier than a gas oven, so does that make a difference?

How about a microwave. Since it's a kind of sealed environment does the moisture really get pulled out of the wood? Jim suggests several short bursts rather than one long one so as not to potentially burn the wood. Full power or lower? Time frame?

I have a pinless moisture meter but I'm not sure how accurate it is without having any flat surfaces to set it against. Any thoughts on that?

Lastly, would a dry rub of herbs and spices be better than basting with olive oil? (Sorry, couldn't resist.)

Thanks.

 

[John Jordan]

If you try to dry it in an oven, you odds of success are very poor. If you try to dry it in a microwave, your odds are poor to pretty good if you accept long learning curve. You can search for threads on the microwave, there are lots of them on the different boards. Some are factual, some are speculation. If you are using exotic (expensive) wood, I would avoid both methods.

Better to keep roughing more while the first dries-you'll soon be far ahead. I'm an advocate of the simplest way, letting the wood dry on it's own. Rough turning/returning is a good way to work. Most of the folks who produce a LOT of work this way, simply let them dry with some simple way of sealing the surface, or in a few cases using de-humidifier kilns. (much different than cooking in an oven)

There's a article on my website that you might find helpful for the basics of this.

John

 

[Dennis Ford]

I would not dry wood in an oven. The fast drying would likely cause cracks.

I have used a microwave before, short bursts is the ticket. Get it pretty warm, take it out and let it cool then repeat (several cycles will be needed). Many woods will cause unpleasant odors resulting in an unhappy spouse unless you have a "shop" microwave.

 

[n7bsn]

I'm on the "never use an oven", never had any inclination to try even.

Now, micro-wave I have and continue to use. Short power cycles (like 1 minute or less) with long cycles between (like 20 minutes) and lots of rest periods (days) between a few cycles. The result is zero failures in any domestic wood I have tried.

It's not real fast, but you really don't want real fast, you actually just want a little faster then natural.

I have been looking at building a real kiln (using a dead refer, plus like a 40 watt bulb and fan), but haven't yet.

TTFN
Ralph

 

[john lucas]

I would not use the oven. I have used the microwave but only on thin wood, 3/8" or less. I have not done but a few bowls . I have done boxes and other small pieces and I follow the 1 minute or less and then let it cool completely before going in again. It takes many cycles and can take all day even on the thin ones.
I do what John Jordan recommends. Just rough out more bowls while these are drying. Within 6 months you'll constantly have dry bowls to work on. From then on it's just a cycle of rough out a few and finish turn a few. If I need one quick I just turn it thin. It will dry in a few days if it's thin.

 

[Tony Latham]

The microwave will dry it out. If you let it run long enough it will get so dry and so hot that it will start smoking and it'll scare the cr@p outa ya!!!!:cool2:

Trust me on this....

TL

 

[MichaelMouse]

What keeps things from cracking is a relatively small moisture gradient interior to exterior. Makes it vital to control relative humidity, especially in a conventional oven. The micro agitates all the molecules simultaneously, so the insulated interior warms and keeps putting out moisture to the exterior, rather the opposite of conventional ovens. Until it's pretty dry, then it lights off. One inch is too thick, in my experience, for micro drying, and for that reason. I use the so-called lower power settings and longer times than others, but it's pretty much the same thing. Magnetrons don't operate at half output, so, as your fan will tell you, they go on for a short burst, go off to allow equalization, then on again, and so forth. The fan can kill you. Bag your piece. NEVER MICROWAVE ELM and make sure you're not using SWMBO's micro.

Kiln operators, working with sort of conventional ovens, monitor the relative humidity closely. I don't think you could do anything approximate in an oven.

 

[pfduffy]

drying bowls

Have you tried boiling the bowls? I am a strong advocate of the process and have experienced excellent results. Put the bowl in boiling water for 1 hr/inch of thickness, let it cool an hour then wrap it in newspaper and stick it in a bag for a couple weeks. Speeds up the process about 50% in time. Microwave works well for thin bowls. Just keep it in a bag, keep the power below nr. 5, and do multiple cycles over a couple hours with lots of cooling time. Start the cycles the next morning and add seconds and increase the power to nr. 6. Keep track of the weight and stop the process when the curve levels out. Phil

 

[Jerry Rhoads]

A few years ago.
I just had to give it a trial, in an oven. The lowest setting in the oven was 170 degrees. Every thing more than 1/2' cracked in less thn 45 minutes. It was too fast.

In the microwave (many cycles on defrost) 1/2 to 1 hour between, any thing over 5/8" is hit and miss on cracking. Up to 3/8", almost always successful. (Sept when I hit wrong button, Makes shop stink.
I am lucky to have a micro wave in the shop. Thanks to being around when an office was being remodeled.

People have told me of their success with a box heated with light bulbs.
Old dishwashers and fridges work for this, or styrofoam on plywood.
They use more than one bulb and raise the temperture every few days or so.
I have not had a chance to try this. But hope to soon.

Jerry

 

[Barry Elder]

Back in the day, I googled "microwave drying for wood" and found 3 very useful articles by woodturners that I found to be very accurate. Remember, wood burns quickly after drying! DAMHIKT!

 

[hockenbery]

I experimented with the oven to force cracks.

My process was to bring the oven to 400 tun it off put the wet Piece from the lathe in the oven leave until the oven totally cools.

this drys and cracks the wood. some pieces would crack in a way that I found pleasing but too many of them just looked bad.
My idea was to create "pottery forms from the dig"

oh well it is only wood

Happy turning
Al

 

[Gary Slater]

In the microwave (many cycles on defrost) 1/2 to 1 hour between, any thing over 5/8" is hit and miss on cracking. Up to 3/8", almost always successful.Jerry

My question is: at what stage of the turning do you microwave? Rough turn down to your 3/8 then dry? Finish turn then dry? What is your process and do you have a reference? Thanks, Jerry.

 

[Thomas Daluisio]

drying wood

I have tried the converted "fridge" the "three bag" "dish soap" and I like the stove best of all....I had to go on line to the stove manufacture to find out how to disable the stoves 12 hour safety cycle.

Normally the newer stoves will shut off in 12 hours, you can change that so it will run until you shut it off.
I jam it full of things to dry so I cut down on the wasting the electricity, Usually let it run for 36 hours and never had a problem with too much cracking or moving, most are burls that I use..good luck

 

[John Jordan]

One can complicate a simple and natural process as much as they like, the time is usually better spent turning or carving.

John

 

[robert davis]

i have dried wet turnings in microwave for ten years rarely have a problem..weigh piece..set microwave on lowest setting..wrap piece in large towel. run for ten min. remove ,leave in towel until fairly cool. weigh piece. wrap in another dry towel. repeat process until piece does not lose weight.. i am talking about a finished turning

 

[Hugh]

There is something sticking up in my brain right now. A story about someone using a microwave to dry a roughed out bowl and it catching fire and burning at least part of the shop? I could be wrong, but I think I read about it some where.

I boil Madrone wood as it is the only way I can get a bowl out of it. But I like air dry. Rough out a bunch of bowls and stack them up. If you need something to turn - go find another tree. A little while later you will have so many roughed out bowl you will not need to speed up the process except to clean up the shop from all the roughed out bowls.

Hugh

 

[jffink]

Boiling, soap-soaking, and heating in ovens and microwaves are fine if your lathe is in your kitchen. Mine isn’t, and I’m sure I’d be in trouble if I tried using the kitchen appliances for woodturning purposes. My woodturning shop is in my basement adjacent to the laundry area, and, after thinking about the aforementioned kitchen methods, I’ve developed a new combination bowl blank treating and drying regimen:

Rough turn to a wall thickness somewhere between 10% and 50% of the bowl’s diameter, depending on how energetic I feel.
When I’ve accumulated several roughouts, carefully place them and my turning smock in the washing machine (I use a front loader — top loaders get out of balance too easily).
Wash using the really hot sanitary cycle with lots of Costco brand green laundry detergent (I think that’s what Ron Kent uses). Add bleach or dye now too if going for such effects.
When the washing machine’s little “your clothes/bowls are clean and I’m shutting down†tune plays, transfer the “treated blanks†(and smock) from the washer to the dryer.
Tumble dry on low using about two boxes of Bounce fabric softener tissues (or the Costco equivalent if trying to either cut costs or stay true to RK).
I figure that the automatic drying sensor should tell me when the bowl blanks are dry.
Remove from dryer and finish turning the blanks.

I haven’t gotten around to trying this yet, as I didn’t buy extended warranties for the laundry appliances. But, in the spirit of sharing that all turners are known to have, I’m throwing this method into the public domain for others to try. Let me know how it works. If your spouse is particularly possessive/conservative about the use of the laundry appliances, you might need to pick up a spare pair to devote to your shop. For people with limited space, or who only turn small bowls, one of those stacking washer/dryer combo units might work well — just a thought.

Happy turning.

John

 

[Rick M]

If you wanna boil but keep your activities out of the kitchen, maybe one of these is what you need .

 

[n7bsn]

If you wanna boil but keep your activities out of the kitchen, maybe one of these is what you need .

It's what I use to boil... Best to time buy one is after Thanksgiving, amazing how cheap they are then

 

[Gary Slater]

i am talking about a finished turning

Robert, I just want to clarify this. When you say "finished turning" do you mean completely down to the finished thickness? You still have to return your piece to the lathe for sanding, right? Can pieces be finished immediately? Do you have a reference we can go to to see the process or would you be willing to post a more detailed outline of how you do it? Thanks for your time.

 

[hockenbery]

One can complicate a simple and natural process as much as they like, the time is usually better spent turning or carving.

John

Do the arithmetic.
I can rough out 2-3 bowls in an hour (I''m slow by professional standards) if I core them I'll have 6 bowls.
Every hour spent boiling, soaping, microwaving..... is 6 less bowls.

No one can rough efficiently when they start out. If it takes you 2 hours to rough out a bowl now, you won't get more proficient unless you turn.

happy turning,
al

 

[Alan Carter]

Thanks for all the responses. So many opinions. A thread on another forum suggested the following: Weigh and nuke the rough turning for 1 min. at defrost. Let cool out of microwave for 1/2 hr. Repeat 3 times and weigh again. Repeat process until weight doesn't change.

I'm trying that right now so we'll see. If I set a timer I don't really lose much shop time and if I do it while watching TV, no loss at all.

I know, I know, if I would just be patient, I wouldn't have to mess with all this to begin with. BUT I'M NOT!!!! So there.

Another small caviat. I don't do production turning, focusing more on sculptural type pieces, so I don't build up a big stockpile of rough turnings. Hence the desire to move along more quickly as I work out the designs.

 

[Gary Slater]

I don't do production turning,... so I don't build up a big stockpile of rough turnings. Hence the desire to move along more quickly as I work out the designs.

I am with you Alan. I have a stock of turning blanks but not lots of time to rough turn then wait. When I want to turn something, it usually means I need it sooner, not later like six months from now.

Besides, that I don't understand one thing. If the general rule for drying wood is based on a formula of one year of time per one inch of wood thickness plus 1, then how do we expect a bowl blank that may be approximately 3/4 - 1 inch thick, to dry in only six months after applying anchorseal?

I am ready to try microwaving.

 

[john lucas]

We all go through the gotta have it now syndrome. I did. that's when I did my experimenting with the microwave. I did but one bowl, I got involved in other things and left it too long. It only smoked it but it took months for the smoke smell to go away. I also ruined a bowl once. There was apparently a hidden sap pocket in the wall. It blew a hole in the side of the piece and the steam burned the outer wall of the piece.
I have looked at the other various means of drying something faster. It all seemed like too much trouble or added to the expense.
I finally decided John Jordan had it right and now I just turn and let them dry.
The hardest part for me is that I start on a piece of wood and want to finish it while it's fresh in my mind. I guess that's why all the various hurry up and dry methods come into play. I'm trying to get over that because as Al said, I'd rather be turning or carving than sitting in the kitchen waiting for the microwave to go off.

 

[MichaelMouse]

Thanks for all the responses. So many opinions. A thread on another forum suggested the following: Weigh and nuke the rough turning for 1 min. at defrost. Let cool out of microwave for 1/2 hr. Repeat 3 times and weigh again. Repeat process until weight doesn't change.

That will give you an overdried piece which will have to rehydrate to regain equilibrium with the environment. Not what I'm after when I micro. Thus the use of the perforated plastic bag. When a cycle produces only a haze in the bag - done. You can safely use longer times on that defrost or low "power" setting, because it will allow the piece to equalize between powered cycles.

Microwaving risks waterspotting as well, so it may make an ugly when all you wanted was a dry.

 

[odie]

Other than the shortened time element, is there any advantage to using ovens/microwaves for seasoning of roughed bowls?

ooc

 

[John Jordan]

One last comment. You don't have to rough turn and return. I've made a living turning green wood for 25 years, I don't rough and re-turn. The pieces aren't cracked, or strangely distorted.

What I'm trying to get across is if one takes a little time to learn about the material, most of this will come easily. People put a lot of time effort into fighting or forcing the wood instead of working with it.

John

 

[Robert Manning]

Accelerated drying

I have used some tropical ash that can be rough turned and set on a shelf with no sealer or bag and it will not crack, but that doesn't mean other woods will dry as easily. Some woods, like snakewood, are extremely difficult to dry and are usually found in very thin pieces. Ebony is not as difficult as some woods, but I still would not be willing to put any in a microwave or oven. I also recommend that you are very careful with the microwave as you can ignite the wood and also get burned by superheated steam ejecting out. Microwaves don't heat things evenly, either. What the microwave is great for, is shrinking small dowels that are oversize in a few seconds. Again, be careful as you don't want to damage the wood and weaken your joint.

I recently dried some hollow forms by wrapping them in a plastic grocery bag. I trimmed the bag so it would tuck into the hollow form opening about one inch. I then took a piece of heavy paper, rolled it into a tube, and inserted it into the opening to hold the plastic bag open. This created a conduit the size of the opening for the vessel to freely exchange air from its center without the rim or exterior drying out. I successfully dried three pieces like this which contained the pith and experienced no cracking. They dried in four to eight weeks which is very reasonable.

I have also experimented with anchor seal by leaving portions of face grain uncoated and totally sealing end grain areas. I have experienced some success here and will continue with this technique.

I also tried soaking many different blanks in a 50/50 soap/water solution. The tropical ash worked well, but as mentioned, it was unnecessary. Some wood still cracked. This technique had the feel of a wild goose chase and I doubt I will pursue it any further.

For the segmented work I do, I require wood that has reached its equilibrium moisture content before I start a project. Some exotics like ebony are rarely available kiln dried and take a very long time to air dry. This is why the vacuum kiln is so attractive to me. Who wants to wait a year for a piece of wood to dry once an idea hatches?

There is definitely an optimum speed that each piece of wood can be dried, and with show deadlines and other demands, I think accelerated drying can be a valuable process.

 

[Wayne Jolly]

I would just like to add my $.02 worth regarding using a microwave oven. DO NOT USE ONE IN THE HOUSE! I had a small piece of Aspen that I wanted to experiment with. As I was going into the kitchen to nuke this piece my wife asked me to help her. So I put my piece in the microwave, set the timer for 30 seconds, hit start and went to help her. A short time later, smoke is POURING out of the microwave oven and filling the entire kitchen with smoke which then spread throughout the whole house. Thick smoke. I had accidentally set the timer for 300 seconds instead of 30. Burned that piece of wood to hell and back. When I took my Aspen out, parts of it were more like Ash. Literally. The worst part was the odors left behind. We tried several things to try and get the odors out of the microwave but nothing seemed to work. It took at least two or three weeks for it to go away.

Xeddog

 

[Joe Greiner]

Here's a list of US patent numbers I've collected on wood drying:
2387595
3811200
4466198
4620373
5852880
6634118

Google patents ( http://www.google.com/patents ) has most patent documents in single file PDFs, simpler than the documents at the patent office. Although the patent office ( http://patft.uspto.gov/ ) has a more robust field-selectable search engine.

Low-intensity commercial use may be under the radar; if in doubt about infringement, consult an attorney.

 

[David Somers]

I almost feel guilty throwing in yet another option, but here goes.

I have to agree with John Jordon that turning from Green straight to finish is a really nice way to work, or rough turning and letting things set for 6 months to a year works very well too. Given a small shop with not a lot of space though I understand peoples reluctance to do this.

I lived in HI for 10 years (and am now splitting my time between Seattle and HI). The folks out there who make their living turning Koa used to do the "rough turn and let it dry" technique. At any given time they had about a years worth of roughed pieces sitting on shelves that ran around their shops. It was pretty stunning to go in there and see this massive number of bowls waiting to be done.

Unfortunately, during that drying time they would lose a significant portion of their drying stock to cracking. They were purchasing their Koa trees and paid big bucks for it, especially the curly so this hurt their margins alot. Plus, they would invariably have bowls returned from Arizona and other dry states when tourists would take their big dollar bowls home. Another consequence of having such a large stock of drying pieces was earthquakes. Hawaii has them all the time and a good one could do in the better part of a years work as your pieces tumbled to the floor. They tried lots of things to get around this problem. They tried the various techniques with Denatured Alcohol, soap soaking, drying racks, PEG, etc. Nothing worked or was worth the expense and bother. These are production turners after all and they make their money on volume as well as quality. (these are high dollar bowls made from the Koa and sold to tourists in galleries)

A number of years ago they discovered a product called Cedar Treat. Also known as woodturners choice. Can be found at www.cedarcide.com. It is a cedar oil product with a carrier from Dow chemicals. (better living through chemistry!) It is rated safe for food contact. Runs about $40 to $45 a gallon and a gallon will do a lot of pieces. A lot!

To use you rough your piece.....of if you are turning straight from green to finish you would put it on after you are done turning but before sanding and finishing. A windex style spray bottle is a good applicator, or a brush. Apply it over the bucket and let the extra drip back into the bucket. Small pieces can be dipped.

For Koa they let it set after that for 3 days or so. For other woods they let it sit for upwards of two weeks. At that time the Cedar Treat has converted the water in the cells of the wood to a stable gel. They then apply their finish and the piece is done. They lose almost nothing to cracking now, even for pieces taken back to the mainland to dry climates. They dont need to have a years worth of roughed pieces on hand drying in order to conduct business.

The cedar smell dissipates after the product is done converting the water. It imparts no taste to food served in the bowl. It doesnt affect the finish whether it is an oil or a shell type finish. It doesnt seep out of the wood over time like PEG can. It doesnt change the color of the wood. Pretty good stuff.

Although I am not a production turner I use it because I like playing with woods that have a tendency to crack when turned or dried. Macadamia Nut and Ohia are good examples. I also use it because I dont have large amounts of space to support lots of drying roughed out bowls while I continue turning other things. I have been very please with it.

The company will send you a sample if you contact them.

Hope this gives you another good alternative for dealing with this issue. In all serious though, consider building up a stock of drying roughed bowls or turning straight from green to finish if you can. Or at least keep that in the back of your mind after you have played with other methods for a while.

Happy turning!

Dave

 

[David Somers]

I almost feel guilty throwing in yet another option, but here goes.

I have to agree with John Jordon that turning from Green straight to finish is a really nice way to work, or rough turning and letting things set for 6 months to a year works very well too. Given a small shop with not a lot of space though I understand peoples reluctance to do this.

I lived in HI for 10 years (and am now splitting my time between Seattle and HI). The folks out there who make their living turning Koa used to do the "rough turn and let it dry" technique. At any given time they had about a years worth of roughed pieces sitting on shelves that ran around their shops. It was pretty stunning to go in there and see this massive number of bowls waiting to be done.

Unfortunately, during that drying time they would lose a significant portion of their drying stock to cracking. They were purchasing their Koa trees and paid big bucks for them, especially the curly, so this hurt their margins a lot. Plus, they would invariably have bowls returned from Arizona and other dry states when tourists would take their big dollar bowls home. Another consequence of having such a large stock of drying pieces was damage from earthquakes. Hawaii has them all the time and a good one could do in the better part of a years work as your pieces tumbled to the floor. They tried lots of things to get around this problem. They tried the various techniques with Denatured Alcohol, soap soaking, drying racks, PEG, etc. Nothing worked or was worth the expense and bother. These are production turners after all and they make their money on volume as well as quality. (these are high dollar bowls made from the Koa and sold to tourists in galleries)

A number of years ago they discovered a product called Cedar Treat. Also known as woodturners choice. Can be found at www.cedarcide.com. It is a cedar oil product with a carrier from Dow chemicals. (better living through chemistry!) It is rated safe for food contact. Runs about $40 to $45 a gallon and a gallon will do a lot of pieces. A lot!

To use you rough your piece.....of if you are turning straight from green to finish you would put it on after you are done turning but before sanding and finishing. A windex style spray bottle is a good applicator, or a brush. Apply it over the bucket and let the extra drip back into the bucket. Small pieces can be dipped.

For Koa they let it set after that for 3 days or so. For other woods they let it sit for upwards of two weeks. At that time the Cedar Treat has converted the water in the cells of the wood to a stable gel. They then apply their finish and the piece is done. They lose almost nothing to cracking now, even for pieces taken back to the mainland to dry climates. They dont need to have a years worth of roughed pieces on hand drying in order to conduct business.

The cedar smell dissipates after the product is done converting the water. It imparts no taste to food served in the bowl. It doesnt affect the finish whether it is an oil or a shell type finish. It doesnt seep out of the wood over time like PEG can. It doesnt change the color of the wood. Pretty good stuff.

The older formulations used to kill boring insects like termites and powder post beetles but I understand the latest formulation does not. I still have lots of the older formula though so I haven't experienced this. Boring insects are a big problem in HI so I am not sure how this will affect everyone.

Although I am not a production turner I use it because I like playing with woods that have a tendency to crack when turned or dried. Macadamia Nut and Ohia are good examples. I also use it because I dont have large amounts of space to support lots of drying roughed out bowls while I continue turning other things. I have been very pleased with it.

The company will send you a sample if you contact them.

Hope this gives you another good alternative for dealing with this issue. In all seriousness though, consider building up a stock of drying roughed bowls or turning straight from green to finish if you can. Or at least keep that in the back of your mind after you have played with other methods for a while.

Happy turning!

Dave