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View Full Version : Microwave drying test - I'm wrapped!!



Phily
19th June 2015, 08:54 PM
OK, per the previous Thread, I have conducted am experiment based on the 3 most popular drying techniques.

My methodology was as follows:

Panasonic Genius 1100w Microwave (a few years old).

3 blocks cut from 2 week old (therefore Very green) Manchurian Pear. Each was turned to a 145 x 55 blank of approx 1kg each

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A 1kg control block was cut from the same block and given a high temperature drying to provide a dry weight target indicator (handy that its winter here!)

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Block 1 was zapped on high for 2 minutes, weighed, left to rest for 10 mins the zapped again for 2 min on high, repeated until 2 identical weights were recorded.
Block 2 was zapped in exactly the same way except that the block was wrapped in T-shirt material - only removed for weighing purposes toward the end.
Block 3 was zapped on defrost for 4 minutes, weighed, left to rest for 10 minutes then re zapped on defrost for 4 min, repeated until 2 identical weights recorded.

Note. I left all 3 blocks to rest overnight (each lost around 40g during this cooling).

Results:
Block 1, 2 min High zap's UNwrapped. Starting weight 1021g Dry Weight 796g. Total moisture loss: 225g
Block 2, 2 min High zap's Wrapped. Starting weight 1028g Dry Weight 737g. Total moisture loss: 291g
Block 3, 4 min Defrost Unwrapped. Starting Weight 956g Dry Weight 734g. Total moisture loss: 222g

Control Block. Stove top dry. Starting weight 1020g Dry Weight 798g Total moisture loss 222g
(note that the control block was also zapped for 1 min on high to check that a "dry" weight had been achieved).

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For the zapping I simply rotated from one block to the next. Interestingly each had a near identical number of zap's to achieve their dry weight.

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As might be expected, the control block started to fracture in quite a number of places - though not as badly as I thought it would.
Interestingly, there were no visible cracks in any of the zapped blocks.
There was very little difference between Blocks 1 and 3. Both had similar weight losses and took the same amount of zapping to achieve their dry weight.

The biggest difference was Block 2 - the wrapped block. After being left to cool it recorded a substantially higher level of moisture loss. It also shrank and twisted quite substantially (check the pictures).

In my opinion therefore, the wrapped approach works best. Requiring the same amount of nuclear power as the other methods a drier timber is achieved - which in my experience results in fewer long term problems (twisting/cracking).

Cheers
Phil

DaveTTC
20th June 2015, 01:20 PM
One question PHIL,

If block two shrank and twisted the most why is it the one you feel worked best?

I'm not disagreeing with just asking.

Loved the overall process and reporting


Dave

The Turning Cowboy

Phily
20th June 2015, 02:25 PM
Hi Dave, many thanks - it was a worthwhile exercise as I have heaps of green timber and now know which way to go.

Ref your question. In the past I have MW dried quite a few different types of timber to what I thought was dry, only to find out later that they still had a bit to go - read plenty of warped & cracked bowls!. My own rule of thumb is that the timber is close to being at the optimal level of dryness from the MW when it has gone out of round/warped. I then leave it to settle for a few weeks. I've never had a problem with a blank using this approach.

I have however lost quite a few blanks during the drying process itself. Hopefully I now have a better technique :)

DaveTTC
20th June 2015, 02:37 PM
Thanks Phil. I concur with your reasoning


Dave

The Turning Cowboy