Microwave Drying

[Rhys Jones]

I am trying to compile a dosier on this technique that can then be provided to all woodturners. I would like to get as many noted on ideas and/or experiences as possible. Also any notes on timbers better suited, or not suited, for this type of drying. All contributions would be gratefully received.

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Rhys Jones
Woodturner

[Gino]

Hi Rhys

seeing someone more experienced hasn't replyed as yet I'll share my small experience with you.
I don't remember where I first heard of drying in this method but it basically constists of short burst with the microwave over ie about 1 to 2 minutes and then weighing the item then re zap it again and again until the weight has leveled off. I.e. the weight no longer reduces.
One important point is to let the item cool down properly before continuing as my bowl developed a crack, probably due to over heating.
If it should over heat the item may develop a burnt spot, this does not take the form of carbon but a change in color of the wood on a particular spot.
the wood I tried it on was silky oak and I managed to repair the crack with super glue.
hope this has been of help.

regards

Gino

[mn2tx]

I have dried freshly cut maple in the nuke. About the same as Gino describes. I used the center of the log in a bowl. The bowl got very oblong but did not crack. I turned the bowl to a uniform 1/4 inchbefore drying.
I also dry segments for bowls before glueing into rings. Works great.

[Badger]

Hi Rhys

I have tried the microwave method a few times (when I’m impatient or haven’t got any normally dried blanks)

The first time was rather interesting! The big secret is to allow the work to cool down between bursts. I didn’t know this at the time and went on merrily belting the thing at half power for two minutes at a time. The base was quite a bit thicker than the walls to allow for rechucking.

On the last time I opened the microwave and was enveloped in a thick cloud of smoke. After coughing my heart up and burning my fingers getting the bowl out, I found the smoke being forced out at high pressure through a minute crack in the base. By the way Gino, although the outside looked fine, I can assure you there was PLENTY of black carbon inside. And BOY did the inside of the microwave stink!!!! Fortunately it was an old one that I had appropriated for just that purpose otherwise the home boss would have given me hell, it took weeks till the burnt smell disappeared.

The material was a piece of spalted willow. I dried quite a few blanks when I first came over to Tassie because I didn’t have any dry blanks and apart from the first miserable failure the results were reasonable but variable. Results with willow were good and macrocarpa works well too. Blackwood very often gets small cracks that open up then close again but large chips invariably tend to fly off these when you try to finish them

Nowadays I stick to my favourite method; wrap the rough turned work up in about four thicknesses of newspaper and leave it for six months of more till it stops losing weight.

It just struck me, I wonder if I could loose weight like that.


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Badger - A gruff short tempered animal that sleeps most of the winter

[Phil Dowthwaite]

Hi Rhys,
I have used microwave drying for the last few years with varying degrees of success. It is a bit limiting because of the size but does work quite well on thin even wall items.(4mm max).
But only on the defrost setting. Any other and you can scorch or burn the timber. ( you will only do it once!)
starting on about 8 mins. Cool. Then reducing the time depending how wet the timber is. Seems to work well on oak, ash, hornbeam acacia etc, does not work well on close grained fruit wood, yew or most of the hard excotics. If you know the timber has any growth stress don't use it, the accelarated drying seems to guarantee a crack.
My wife has just read this over my shoulder and pointed out that to maintain matrimonial harmony get your own micraowave.
Hope this helps.
Phil

[rsser]

Hi Rhys,

If you do a Google search on newsgroups you'll find a heap of postings on rec.crafts.woodturning

See also drying by boiling and burning (yes, believe it or not).

I've tried it on a 1" thick piece of of Australian flowering cherry and the results weren't too hot :-)

Cheers,

Ern

[Gino]

Phil

I think we're married to the same woman.

regards

Gino