Drying timber...

7 July 2013, Woodturning in practice, Would you like to leave a comment?

This really has taken me years to work out and is certainly very frustrating when I get it wrong! It would be uneconomical for me to buy large quantities of kiln dried timber, so preparing it from green myself is without doubt the best way forward.

The thick slab of walnut shown below is destined to become a bowl in the future, but will never dry out in its current form – certainly not within a realistic period of time. As mentioned in previous posts, it has to be processed and rough turned into a blank.

Walnut-slab.jpg

The slab now rough turned, sat alongside its siblings ….

Walnut-bowl-blank.jpg

Every blank I turn is stored in my shed for seasoning, a process which varies in time. Each species has its own rate of drying and this differs considerably. At one end of the scale is beech, which cracks easily and can take many years to dry. However, ash and elm are both quite resilient to heat and can even be kiln dried from green – although I would never recommend this! Burr wood is probably my favourite, since the natural cracks and holes offer loads of spaces for air to get in and water to vaporise out. I do like turning burr!

I use a moisture meter to check the water content at key stages of the drying process. Green wood can vary between 35% and 50% moisture content, or sometimes even more. After about eight months in my shed, the average blank will be down to 25% and ready to go into a drying kiln. There is a risk of timber cracking if it is kiln dried when too wet.

The kiln gradually heats up to about 60 degrees and takes between ten days and two weeks to bring the moisture content from 25% to 12% - just right for the final stage of turning.

The kiln at Df Timber, which I am luckily allowed to use!...

Drying-kiln.jpg

The very top image is of my seasoning shed. Notice the plastic sheet covering over the beech – this was rough turned nearly two years ago and is still wanting to crack. Timber can be unpredictable at times and does need to be checked on a regular basis - especially when the weather is hot. However, most of the drying problems I’ve encountered in the past have now been solved – it really is just a case of learning. The wooden shed where my freshly turned blanks are stored, now has its windows boarded up, cutting out harmful rays from the sun. I now do the bulk of my turning in the winter, so by the time summer comes around, my blanks have had a good few months to stabilise.

Just when I think I’ve got it sussed, I’ll end up with a few surprises – not that I ever look forward to them! The image below is of some cherry I turned during a hot spell, last spring. Unfortunately, the change in temperature was too quick and the blanks split fairly quickly...

Cracked-cherry-blanks.jpg

Jonathan Leech

Written by Jonathan Leech

Jonathan Leech is a woodturner working and living in Cumbria. He specialises in making bowls, dishes and platters from local sustainably sourced timber. Read more or about Jonathan or see a selection of his work.

Your comments

  1. Gravatar of Mike
    Mike18 February 2014 21:05

    Jonathan,

    It pains me to see those cherry bowls split so badly. I turned four hickory bowls in late December and three of them are already badly cracked. Hopefully the last one will make it!

    BTW, I really enjoy your blog and am totally jealous of your VB36!

  2. Gravatar of Jonathan Leech
    Jonathan Leech19 February 2014 09:45

    Hi Mike,

    It's so frustrating when wood splits - it's not just the waste of wood, but wasted time! I have problems too with beech, so now keep it wrapped up in plastic for months at a time.

    I'm so pleased you like the blog. You've got a fantastic website and your post on the vacuum chuck is excellent - will it grip larger pieces?

    All the best, Jonathan

  3. Gravatar of Mike
    Mike19 February 2014 15:50

    Jonathan,

    Yes, I'd feel comfortable with plates around 16" using the vacuum chuck I blogged about. It doesn't take too much work to make the chucks, so a larger drum could be fabricated without much fuss.

    Regards,

    Mike

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