Micro waving pieces

[Phil Labowski]

I've wondered about this for awhile and now that I actually have a roughed out piece I'd like to finish... do you use your regular microwave for drying blanks, etc. or do you have an old one in your shop? I'm sure you can imagine the poo storm that would happen if I ruined the microwave trying this. Also, I have one of those "Nu-Wave" ovens and was wondering if anyone had tried one of those. Thanks in advance gang.
Phil

[Grant Wilkinson]

I've only tried it a couple of times, so I used the micro in the kitchen. I used the slow method, and put the piece in a paper bag. There were no issues with the oven. I looked at the fast method, using a plastic bag. I didn't try it, and would not in the kitchen microwave. It just looks too iffy to me.

[Steve Busey]

I picked up an old microwave at a thrift shop for a few bucks. Ask your friends - they may have an old one sitting in the basement after they upgraded the kitchen to a bigger unit.

[kevin nee]

I micro-wave 1 minute a day ( have had great success ) Since I got a big micro-wave for the shop my wife is happier. GOOD LUCK!

[Michael Kellough]

I've wondered about this for awhile and now that I actually have a roughed out piece I'd like to finish... do you use your regular microwave for drying blanks, etc. or do you have an old one in your shop? I'm sure you can imagine the poo storm that would happen if I ruined the microwave trying this. Also, I have one of those "Nu-Wave" ovens and was wondering if anyone had tried one of those. Thanks in advance gang.
Phil

I've been reading about microwave drying too but don't have any experience yet. From what I've read about how microwave ovens work yours is a good one to try this on since it would put out continuous low energy (if you set it to a lower setting). Older microwave ovens use a full power magnetron that is turned off on a regular basis depending on how fast you want to cook/dry.

Seems to me the best MW oven for drying is one of the new inverter driven continuous variable power (= Nu-Wave in marketing-speak) units that has a rotating carousel.

Next best would be a standard MW with a rotating carousel whose rotation is synced with the increments of MW operation. That is, if the magnetron is set at 10% power and a period of rotation of the carousel is ten seconds then it's a good match. A bad match is when the rotation and power periods get "stacked" so that the magnetron shoots the same spot on the piece over and over even when on the "low" setting. Most MW ovens are designed to avoid this pattern but be aware.

The worst MW for drying is the old non-rotating platter with a full power magnetron. Left unattended you'd burn a hole in the side of the piece. On the other hand if you take full manual control and are careful you could get good results.

If you try it post the results.

[David DeCristoforo]

You might want to read Marshall Gorrow's article on microwave drying (http://mgorrow.tripod.com/microwave.html). It's short and sweet but very concise. I followed this protocol recently when trying this for the first time and it worked very well. DO NOT use your kitchen microwave for this!!! It will begin to smell of wood almost immediately. I picked up a used microwave at a yard sale for $5.50.

PS Watch out... Marshall's site is on Tripod dot com and it throws off some "in your face" ads!

[David C. Roseman]

Michael Kellough wrote:
The worst MW for drying is the old non-rotating platter with a full power magnetron. Left unattended you'd burn a hole in the side of the piece. On the other hand if you take full manual control and are careful you could get good results.

Exactly what I have in the shop. :) An ancient Monkey Wards hand-me-down with a spring-loaded kitchen-timer dial. No power options. Works great so far on small roughed-out pieces. One minute in an unsealed plastic bag, remove from bag and let cool; repeat a few times. YMMV.

David

[Ralph Lindberg]

I routinely use a microwave to dry. The only wrong microwave is the wife's. The best ones are the free ones you can snag from friends that don't want that big one they had in the kitchen. The above sited article is certainly a good place to start and I saw nothing that I could disagree with. Not that I do it exactly that way, just that it's not "wrong".

You do need to adjust your power/just sitting cycle per the load and power of the oven to what you are drying. This requires a little experimentation with your particular unit. You want to avoid overheating the wood (tempering in wood drying parlance), besides avoiding cooking the wood to the point of charring the wood.

You also need to vary the time according to the amount of wood. I usually try wood in the full-power settings. Which means for a small object (say under 100 grams), the "cook" cycles are very short, maybe on 10 or 20 seconds. On the other hand I have six blocks of Red Alder (3x3x6) that I am currently drying from soaking wet to dry enough for the DW to practice boxes with. When I started they weighed 3250 grams, they now weigh 1820 grams. The cook cycle for these is 120 seconds (at full power). What I have found for this microwave is the weight ( in grams) divided by 20 gives a reasonable time.

Now the last microwave (a Sharp Carrousel) had a different time (it died, they all do, eventually). I have also noted that as these things age, the time changes (going up, as the actual output power goes down).

A shop microwave can be a useful asset.

[Michael Kellough]

Ralph said, "What I have found for this microwave is the weight ( in grams) divided by 20 gives a reasonable time."

That sounds like a very good starting point for analyzing the results and developing a formula. You could vary according to initial moisture content and species. With experience know which species don't conform to the formula and which kinds of grain need special care. Like, maybe a knot needs to be covered with foil.

[Harry Robinette]

Please lets ALL remember to have a fire extinguisher handy and watch the dry wood can be much hotter on the inside then the outside.
Just Thinking.

[Dave Mueller]

When you microwave wood, the water becomes more mobile, but is still in the wood. I have a vacuum chamber I got from Turntex for stabilizing with Cactus Juice, and decided to try using it after microwaving. It really works well. When you get vacuum lower than ~25", you can see all the moisture come out of the wood and condense on the vacuum chamber. For a small roughed piece (<6" dia bowl 1/2" wall thickness) I microwave for one minute, then vacuum for about 3 - 5 minutes. Since I have a HF oil pump, I then open the vacuum chamber, wipe out the moisture so it does not contaminate the pump and then go at it for another few minutes. If you measure the wood moisture before microwaving and then after vacuuming, it is clear that the moisture is migrating to the surface. Do this a couple of times a day and the wood will be down to <10% in just a couple of days. I did it with mesquite, which is pretty free from checking and warping during drying, but haven't tried it with other woods yet.

This technique makes sense, since one of the older methods for drying wood was vacuum kilns. I haven't tried it without the microwave heating, but assume the heating helps. If anyone else tries this, please post your results.
Dave

[Phil Labowski]

wow, thanks for the response gang! I'll have to check on "free-cycle" and watch for a nuker. When I said Nuwave this is the oven I was referring to: http://www.nuwaveoven.com/. I might cut a blank and try drying it in there, but with my issues I can't risk a roughed out piece.

[Dan Jechura]

I have tried drying a bowl blank an had worse luck that I did drying a rough out bowl. Less mass. I use the 2 to 3 min on defrost only, let sit for 30 min. and do it again until meter says 10 to 8%

Dan

[Phil Labowski]

So a moisture meter and/or scale is something else I need to invest in? Anyone look at the "Nu-Wave" and have any feed back about using it? My fear with that idea is how fast that thing can cook stuff.

[Ralph Lindberg]

Phil, in my opinion neither the pin type, nor the induction type are really needed for drying wood. Neither really reached "deep" into the wood.

Weigh and record works with any wood, any size, finished or raw.

I keep microwaveing until the wood either hasn't lost any weight (after resting a day or two), or is a bit higher.

I actually own a pin type that I bought from Harbor Freight fairly cheap.

[Phil Labowski]

Thanks Ralph, I figure the piece would catch fire in the nu-wave. Now I just need the wife to no be home for a while so I can nuke that bowl. lol