If this is your first visit, be sure to check out the FAQ by clicking the link above. The main advantage of a kiln is that with the increased temperature and airflow—all while carefully maintaining and controlling the ambient humidity—the wood can be dried much more evenly, minimizing any sort of moisture gradient between the outer shell (which dries very quickly) and the inner core (which slowly equalizes moisture with the shell).
The simplest and best place to start would be to take your rough-turned bowl off the lathe, put it into a brown paper sack or box and pack it in the shavings that were created while turning it. Now every few weeks you can check the weight of the rough-turned blank to see if it is still losing weight, once it no longer loses weight, it should be dry and ready to remount on your lathe to finish turning.
I think the single biggest help would simply be to know what the MC the wood is currently at. Beyond this, as a general rule, I’d recommend starting outdoors and moving indoors after several months — it all depends on what the MC of the wood is at. Tarps aren’t ideal, but yeah, you should try to keep it somewhat protected from the elements — direct sunlight as much as rain.
The way to determine water content is usually by jamming an electronic probe into the side of the board on an inconspicuous surface, but if you know how much your wood should weigh dry versus wet then you can determine water content by weighing it. I suppose that tip is more useful for people using very small pieces of wood who don’t want any surface marred by test probes.
Drying wood is a very wide and well debated subject (just like selecting wood finishes) so I will tell you what I have learned from my experiences. Light color woods which have been shrink-wrapped may show signs of staining or spalting if this is a problem, remove from the shrink-wrap, rough out the turning. After that the MC will rise and fall as the RH of the air rises and falls – with the change in MC so the wood will expand and contract.
Experience has taught what works for me, Borrow two real estate terms to describe my outlook on drying wood. Just as the name implies, the wood fibers grow in a twisted or interlocking manner. I’ve some background understanding of drying processes and wood moisture content, but am wondering if you guys can offer some advice on how best to approach this question.
If the kiln is not full to capacity I normally put a bucket of water in to start with to get the humidity up.I bring the moisture content down to about 8 /9 % which ensures stability in the end piece. I tend to take things slowly in the kiln which means that it is easier to turn on the lathe. Yep the old box with a light for heat and venting work just fine, more of a conventional kiln.
A good rule of thumb is the wall needs to be 10% of the bowl diameter, or less. 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 beauty of this method is a bowl would be dried in 3 to 5 weeks and be ready to be finished turned.
Not sure how it would work with blanks but may be worth a try on something cheap. One huge crack can appear in a wood like pine, while elm or beech will have a myriad of small cracks, as in the photo at right. 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. These woodturning packs are presented in a box and can be sent throughout the mainland UK by carrier.
For anyone with the time and space to store green timber blanks this can be a source of free hardwood, so if you are out and about and see someone cutting large trees its often worth asking if you can have some of the branches as quite often they are just going to dump the wood. Turning green wood is kind of a messy affair as depending on the wood and its density can leave you soaked in sap that gets flung out by centrifugal force when the piece is spun on the lathe. You need a relatively large quantity of bowls in the kiln to ensure you have plenty of moisture in the air for the early stages of drying if not it can have the same effect as putting your bowls out to dry on a windy day.
Turn the bag inside out and put the bowl back in it. Repeat every 2 or 3 days until moisture no longer collects inside the bag, then leave the bowl out to finish drying. A hallmark of poorly processed, do-it-yourself lumber is the presence of spalted or partially rotted wood. Mount the blank on the lathe, typically with a screw center chuck or faceplate fastened to the top of the bowl blank.