First go at drying green wood with a microwave

[PAC]

This weekend, I finally managed to bolt my grinder down to the bench and add a jig. After a couple of failed attempts at sharpening my tools properly, the penny finally dropped and now I'm getting long, single-facet bevels .

With sharp tools at the ready, I had a go at my first green turning. I attacked a freshish piece of walnut with a bow saw and attached it to the screw chuck. The wood wasn't long enough for a goblet so I decided just to make the cup bit at the top of the goblet, for a bit of practice. There were long ribbon shavings flying all over the place. :shock: The finished item has a base and kind of looks like a large egg cup (which would make a good dice shaker for my daughter. ).

The upper rim is about 3mm thick and the base is about 20mm thick. When I'd finished, it felt quite damp to the touch so I decided to zap it in the microwave. At the start it weighed 126g. I stuck it into a sealed plastic bag (after ensuring Mrs. PAC was out of the house) and microwaved it for 30 sec. The bag filled with steam. I removed the wood from the bag, wrapped it in kitchen roll and left to cool for 5 mins. After re-weighing it had lost 4g of water. I repeated the process 10 more times and the final weight settled out at 84g.

I was amazed how well the wood dried. No splits or cracks at all. I did get some slight warping so I returned it to the lathe and used a scraper to return it to its former glory. I found that the chuck nicely held the base of the wood to allow me to finish the top half but I need some way of holding the the rim of the vessel, in order to finish the bottom. Robert Sorby do a good set of jaws made from aluminium with little pegs in to grip the wood. Might have a go at making myself a set next weekend...

 

[Paul.J]

Sounds good Paul.
I have only tried Microwave drying once with a piece of Hawthorne,and it split terribly.
Might try a turned piece though and see how it goes

 

[maltrout512]

When I read your post first and you had mentioned that you put the turned piece in a plastic bag. Why was your reason for placing in a plastic bag? You then said that time wise was 30 seconds at what power?
You them went onto repeat 10 more times. Was this at the same power? Sorry for all the questions, I have done some test with drying with a microwave and would like to know in a little more detail your posting.

We all learn something every day.

Many Thanks

 

[PAC]

I used the technique described here - http://www3.sympatico.ca/3jdw8/microwavedrying.htm

The plastic bag is there to protect the microwave oven from the wood (don't want my food to taste of walnut, yew etc.). I used full power (1000W on mine) and watched through the window to see when the bag had fully inflated (the oven was set to heat for 2 mins but I stopped it at 30 secs when the bag was full - this time will change depending on the size of the piece). I then used 30 sec and full power for every microwave session. When you open the bag, steam comes flooding out so watch your fingers. Wrap the piece in kitchen roll to slow down water loss and weigh after 5 mins of cooling. My turning lost between 4 and 6g each session. Repeat the process until no weight loss is recorded. When my piece's weight fell to 84g it did not lose any more weight (water) on the next heating session - so I stopped there. If you continue to heat after this point, the wood could become too dry.

Apparently, heating (steaming) the wood in this way reduces the chances of internal stresses from splitting the piece. Hope it works for you too.

 

[Woodmagnet]

Many thanks for the "how to" Paul.

 

[maltrout512]

Thanks for the "how to" Paul. I had thought it strange when you said that you put the bit of wood in a plastic bag to stop the smell of the wood. I have not had this problem, but there again I'm not married. But I can see the other reason behind putting into a bag. The moisture is given off at quite some rate for a few blasts in the microwave so what I see the plastic bag doing is retaining moisture /steam in an enclosed area with the wood instead of being blasted out of the microwave while cooking in the normal manor. This then reduces the moisture loss each time, and should stop almost any splitting of the wood.
If you see what I mean.

Anyway Thanks again

 

[PAC]

But I can see the other reason behind putting into a bag. The moisture is given off at quite some rate for a few blasts in the microwave so what I see the plastic bag doing is retaining moisture /steam in an enclosed area with the wood instead of being blasted out of the microwave while cooking in the normal manor. This then reduces the moisture loss each time, and should stop almost any splitting of the wood.

Yep, that seems to be the other reason. The original website also suggests using a microwave with a simmer function, where you just blast the wood in a pierced plastic bag for about 15 mins. Again the bag will help to prevent too high a rate of water loss.

The microwave technique seems to work really well. I'll probably give it another try at the weekend.

 

[Vulthoom]

I tried this yeaterday with a rough turned green Hawthorn bowl.

I think I must have been too enthusiastic with the microwave because the endgrain opened up magnificently!

Less zapping time and more kitchen roll next time.....

 

[PAC]

I think I must have been too enthusiastic with the microwave because the endgrain opened up magnificently!

Oops, sorry to hear it didn't work. I'll try again this weekend and let you know how I get on.