Drying a Large Block in the Microwave

[Mark Jundanian]

I am wondering if anyone has any actual experience with microwave drying a bowl blank. I am not asking about drying a turned bowl, that is commonly done, but instead drying an unturned large square block of wood.

I have found a source for 5 inch thick bowl blanks, but the wood is wet and waxed. I am informed by those who are in the kiln drying business that wood that thick will take forever to dry, will probably crack and may retain moisture deep inside. Air drying would take maybe five years.

Hence the thought about microwave drying. I am envisioning a cycle of brief heating followed by cooling and equilibration, then rinse and repeat. I am also wondering if microwave energy might not get deeper into the wood for more thorough drying.

Any one with real world experience? Any other idea on how to dry say a 10 x 10 x 5 block?

 

[Gary Beasley]

Its so much simpler to rough turn it wet then dry it. Problem with the microwave is even though you can get the wood heated inside getting the moisture out of the wood without damaging it will take some time. You have to be careful you dont scorch the inside of the wood while youre at it. Ive tried with pen blanks and even then the results are iffy.

 

[Doug Freeman]

Agree with Gary. I have done some successful mw drying and some unsuccessful. Nothing the size you asked about. Chance of cracking is fairly high due to heating water down inside the wood. Too easy to rough turn wet and let it air dry. Better off drying the rough turned piece in the mw vs the whole piece. What is your aversion to turning wet wood?

 

[Owen Lowe]

What type of wood(s) are we talking about here? Once we know that, you may get alternate suggestions for successful drying. For the record, I don't think microwaving whole blocks would be successful for the reason Gary commented. It's such a large volume that I think the block would be heated unequally and not allow water vapor to escape in a balanced manner.

 

[Mark Jundanian]

I am not turning bowls or platters or for that matter anything useful. The forms I do turn would not be particularly forgiving of any distortion in the drying phase and the process I use to make them does not permit twice turning.

As to what species, the usual suspects, maple, sycamore, cherry, ash, etc. I don't like any kind of oak, and I wouldn't choose poplar, either. Sapele, or even khaya (african mahogany) could work, too. If there is a species of wood that would work better I could look at that.

 

[John Torchick]

There are those who convert an old dishwasher or refrigerator to a kiln. Plus there are solar kilns if you have room outside. Saw a video of famed woodturner, Glenn Lucas, who had an entire building full of bowl blanks. Bigger than some apartments I have lived in.

 

[Mike Johnson]

Newer industrial wood kilns utilize microwave technologies to speed up the drying process for commercial use and drying of lumber. Supposedly they can load mixed batches of wood to the kiln and the different types of wood with different moisture contents will come out "dry". Most operators I know of still like to air dry their wood for a few months prior to going into a kiln.

 

[Gary Beasley]

If you do try, and theres no reason why not, cover the blank with thick paper so the humidity inside the wood stays more even as it is heated dry. That will give you a better chance to avoid cracking. Leaving the wax on might be an option if it weren't prone to melting and running off all over your microwave.

 

[hockenbery]

What you might try if it works with your final form is to hollow the blanks then dry them. The dried block can then be machined or turned.

 

[John Jordan]

You're unlikely to have success with a microwave with wood that thick, there's just no way to even the drying enough. Rough turning is the way to go, and will dry in a matter of weeks to months. Some folks do have success microwaving roughed out blanks, but even that is iffy.

John

 

[Mark Jundanian]

Leaving the wax on might be an option if it weren't prone to melting

I think it would melt, I could try something else on the end grain like latex paint.

hollow the blanks then dry them.

I might be able to bore some out with a Forstner bit. Well for some shapes, not others.

 

[robo hippy]

Well, what are you turning that would make the twice turned process not 'user friendly'? That would be the most efficient way to dry the blanks, and to get consistent results. Pretty much impossible to dry anything over about 2 inches thick so that the moisture level is constant through the whole piece.

robo hippy

 

[Karl Loeblein]

One way to dry thicker blocks is with multiple passes through a vacuum kiln/ Might need to allow a few weeks between passes in order for remaining moisture content in the block to equalize. If you can spare $500 to $1,000 then might be able to build a DIY Vacuum Kiln like the one at this link: https://www.instructables.com/id/Vacuum-Kiln-or-Atomic-Bomb-you-decide/

Another parting thought...If grain and color need to be similar then try cutting a thick block in half (or thirds) with a thin bandsaw blade. Dry the thinner boards using any number of methods (i.e air dry or homemade drying kiln), and then run boards sparingly through a planer to re-flatten them after drying. Finally glue the thinner dry boards back together into a larger turning block before turning.

 

[Mark Jundanian]

Today I was talking to a turner in MN who regularly turns massive blanks (hundreds of pounds) and who has considerable experience drying large heavy pieces. He's used a giant microwave in the past, but now feels that vacuum kilns are the way to go and might work for me. Although with the proviso, that it's no slam dunk and there will be plenty of risk for cracking. I ordered the book on vacuum kilns by Joshua Salesin, so that will be a place to start. Thanks, the instructable was very interesting.

Laminating up pieces is another option (as is sticking with 4 inch designs), but I don't think I will like the look. Might be able to vary species and even go with more layers, but that might end up being "a lot to look at".