Microwaving Bowls

[Jonathan Emerson]

Brand new to this hobby and have been doing a lot of research. I eventually plan on building up a stock of rough turned bowls that have slowly dried, but until then I have been trying my hand at microwaving. I have been developing some small cracks on a few of the bowls that are rough turned, the ones that are finish turned have microwaved great. One thing I thought of and wanted some feedback is spraying the end grain with water before and after microwaving in order to slow down the drying there. Does that make sense or is it not doing anything for the process except making it take longer? I also want to try dish soap in the future, but I think my wife is getting tired of all these little purchases adding up. Any other tips on microwaving success for 1” thick bowl blanks? Thanks in advance, I have already learned so much from this site.

 

[John Walls]

Welcome to the forum!

I microwave wet small bowls every once in a while. After a few times with piss-elm, wife bought a new micro-wave and said get that stinky thing out of here (still not sure if she meant the wood, old microwave or me... LOL), now I have one in the shop to use. I have found if I hit it for 60 to 90 seconds, I don't get many, but do get some cracks mainly from pith or knots. I tend to think the cracks were already in the wood just small enough to not be seen. I occasionally will do a bowl a second time for 60 seconds after letting them cool a bit but that is where I start having bowls warp, some slight and some like a football. For that reason, I try to have my bowls finish turned before nuking, if it has alot of character or special wood, I will just sand/finish from there, or just throw in the fireplace. Out of round adds character. On blanks I take a shower while turning, as like the other day.... all I manage to do when pushing my luck is start one smoldering in the micro.... not fun... and still a little too wet LOL. I agree with your wife about all the little purchases adding up... it's not a cheap hobby (all my wood is free) but oh so much fun!

 

[hockenbery]

Most people microwave a few bowls when they start. I did. Then it gets tiresome and you resort to it in a rare situation where you need to finish a bowl in a hurry for some reason.

water on the endgrain won’t hurt. I rinse my once turned bowls in the shop sink and towel dry to get the endgrain hydrated a bit before putting them in a box to dry.

I had success with a little bee’s wax on the endgrain before microwaving
I let the bowls rest between microwave cycles
3 minutes at 40% power rest 20 minutes. repeat the cycle until there is no dampness.
A 10 inch bowl with a 1” wall will typically need 6-8 cycles

my recommendation is to air dry bowls for twice turning to build up and inventory of dried bowls, Every few bowl’s make make a once turned bowl you can finish in a few days.

A natural edge bowl with the bark taken off( it is more work) with a 3/16” wall will dry in 3 days.
Without the bark they are often more elegant looking and the owner will use it functionally.
A day in a box with the flaps closed, day with one flap,open, a day on a shelf. Sand and finish.

 

[Robert D Evans]

I tried microwaving a bowl once but I got caught. Apparently, I am not allowed to microwave bowls without food in them. I have a bunch of bowls air drying now and I continue to add to the collection. Eventually, I'll have a stockpile I can pull from. It just takes time.

 

[Dean Center]

Jonathan, one way to address the lack of dried bowl blanks is to turn the green wood to a finished bowl. You have to turn it pretty thin, so in some ways it's more challenging than the two step method. In two very important ways, however, it's much easier and better--green wood is easier to turn and there's less breathable dust. The bowl will warp, with the amount determined by the type of wood, so the finished result won't be the same. Some people think the less uniform bowl is an improvement. You might give it a try.

BTW, Go Cubbies!

 

[Bill Boehme]

While we normally think of microwaving as being a fast process ... for cooking food, it is a tedious and not so fast process when drying wood. The downside to accelerating the drying process is that it results in case hardening. Case hardening, simply stated, means that the wood near the surface is dry while the inner wood is still wet. As the inner wood dries, it shrinks while the dry surface wood is unable to move without developing cracks. The cracks are often too small to see and sometimes very large. The procedure described here could be considered a slow way to dry wood fast. I've done microwave drying a few times, but it has been at least a dozen years since I last did it. I don't really care for the process because of the high failure rate, but I think this method gives better results than some of the pants-on-fire methods that I have read about over the years.

There is one thing that will help reduce cracking tendencies in any piece and that is to turn a uniform thickness. This is true whether you do a two-step process (rough turn, let the wood dry and then finish turn) or you turn green wood to final dimensions. It is not possible with some designs to have a uniform thickness but when you can, it will help the wood dry more evenly.

Start by turning green or partially dried wood into a bowl shape. Once you are satisfied with the shape, cut the sides of the bowl to desired thickness. I prefer a thickness of one-eighth to one-quarter inch. Sand the bowl to 220 grit. If the wood is extremely wet, it may be better to sand it after drying. The foot on the base of the bowl can be left on to allow sanding after drying. If the bowl will be left unattended for more than an hour during the turning process cover it with a plastic bag to prevent cracking.

Microwave Drying Procedure:

1. • Cover the bowl with paper towels and a dish towel and place in a plastic grocery bag.
   • Tie the bag loosely to let air escape and place in the microwave.
   • Set the microwave oven to low power. (Level 1 or 2 out of 10)
   • Set the timer for 2 minutes.
   • Start the oven.
   • When the microwave stops let the bowl sit in the bag in the oven for 10 minutes.
   • Take the bowl out and unwrap it. The bag and the towels will be wet.
   • Let the bowl sit uncovered for 20 minutes. Check it for cracks – glue up if needed.
   • Rewrap with dry towels and continue drying until there is no water on the bag.
2. Large bowls (up to 14 inches) take 6-8 turns. Small bowls 4-5.

You can spread out the drying over several days by drying a turn or two each day and then covering the bowl with towels and plastic to wait till the next day.

 

[Peter Rowell]

Place wood in loose plastic grocery bag IOT keep the outside of wood wet.
2 minutes in microwave on high to heat up the wood.
10 to 60 minutes at 20% or less to continue slowly vaporizing moisture. Repeat.
Make sure to remove pith and at least more than several growth rings.

Guaranteed to turn mesquite into severe ovals. Osage must be done slowly.

When in a hurry I will turn thin, place in plastic grocery bag, heat in microwave, cool in vacuum chamber, weigh and repeat.

Currently experimenting with heating linseed oil to 120 F inside my vacuum chamber, submerging a bowl, and drawing a near perfect vacuum.

 

[Karl Loeblein]

Searching the forum for threads on ‘microwave drying’ might turn up some useful tips.

Here’s one for example:
https://www.aawforum.org/community/threads/black-cherry-wood.16942/#post-171237

 

[Dave Hulett]

Jonathan, one way to address the lack of dried bowl blanks is to turn the green wood to a finished bowl. You have to turn it pretty thin, so in some ways it's more challenging than the two step method. In two very important ways, however, it's much easier and better--green wood is easier to turn and there's less breathable dust. The bowl will warp, with the amount determined by the type of wood, so the finished result won't be the same. Some people think the less uniform bowl is an improvement. You might give it a try.

BTW, Go Cubbies!

That is my method. I'm in the process of turning a dozen or so small 5-6" natural edge bowls for Xmas gifts filled with candy. All from a 3ft 6-7" diameter cherry cut a few weeks ago so very wet. I cut and turn them down to less tha a 1/4" taking care to keep the thickness uniform, including the bottom. When I get to 1/4" thick, I turn a hair dryer on them for 7-10 minutes inside and then outside while still on the lathe, sand, reverse chuck, hair dryer on the bottom for 5-minutes, then finish and sand the bottom. I then put on a coat of wipe on poly every 60-90 minutes. usually takes 2-3 coats. All this done start to finish (on a small 6" bowl) takes 2-3 hours. have turned perhaps 3 dozen or so like this over the last 8 years and never had one crack. They will warp, but that's inevitable. But once you start on it, you have to see it through immediately. If something interrupts you it is ok to shrink wrap it and finish the next day.
have microwaved a few but haven't found it to be worth while.

 

[hughie]

Microwaving and all that. I had a go at it and found that some of the different species needed variations the program and given that now my stash is largely dry and well seasoned. I have largely given it away although I still have the microwave in the shop.... just in case

 

[Tim Connell]

When I started, I waxed all the bowls I roughed turned and would wait 6 months to a year to finish turn them. Now everything rough turned goes into paper grocery bags (sometimes doubled) and depending on the wood and size, can have those bowls ready to finish turn in 6-8 weeks for almost anything 11"and under. Never tried microwaving, just seemed like too much of a PITA for many of the reasons listed above.

 

[hockenbery]

Never tried microwaving, just seemed like too much of a PITA for many of the reasons listed above.

I too adopted paper bag drying last century when a club member tipped me off to it.

Microwave drying can work to fill the gap for new turners who want a finished bowl in a week. Or a long term turner who has a quick job for some reason.

Often new turners lack the skill to turn a NE bowl which is near instant gratification. Bowl ready to finish in a few days.