Article 3 dealt with completing the rough turning of the Natural Edge Bowl; you have rough turned both the inside and the outside of the bowl and you are ready to dry the bowl. We will discuss several ways to dry the bowls also how to finish turning the bottom of the bowl and final sanding.
There are a number of ways to dry your bowl. Many wood turners will continuously turn bowls and place then in a cool dry location with moderate temperature and good air circulation to dry; this process will take about one year. This method allows you to create an inventory of bowls at very stages of dry; you will always have a dry bowl ready to finish. I never liked waiting a long time for wood to dry so I built a small Wood Kiln; see below. This kiln will dry a bowl 1 inch thick in 7 to 14 days all depending the amount of moisture to be removed and the amount of wood that is in the kiln.
Other ways to dry green wood is to microwave the wood in short bursts until it is dry; it is very easy to burn the wood. On a very small scale this might be OK. Another way is to place green turnings in dry wood chips, works well but again this process takes time.
Let's jump ahead and start working on our dried rough turned bowl. Some types of wood will have small checks, these can be turned out. There will also be some warping which can also be turned out. Some species wood will crack and warp no matter what you do, Pacific Madrone (Arbutus menxiesii), is one; very petty wood. The only way I have been able to dry this wood is let it slow air dry and then work around the cracks and warping.
Your bowl has been finished both inside and outside and sanded to least 250 grit. Some wood turners will sand way out to 600 or more, this can be a reduction to your project because the finish will not stick to the wood if it is too smooth, read the manufactures instructions. Most finishes; waxes, varnishes, oil, water based products and lacquer all recommend sanding the surface to 250 grit. One of my favorite finishes is "Dalys Profin", Gloss; This is a wipe on and wipe off oil product, leaves a very nice finish.
The final step is to finish the bottom of the bowl; this is called reverse chucking. There are mega or jumbo jaws available that will attach to your scroll chuck; the shape of the edge of the bowl will make or break your ability to hold the bowl in the chuck. If your bowl has a smooth even edge the jumbo jaws are good. My preferred method is vacuum chucking, as long as the bottom is smooth with no holes it is bullet proof. At sea level a six inch vacuum cup has about 400 pounds of holding force.
Centering the turning on the vacuum chuck is the hardest part. The best way to center the bowl on the vacuum cup is to use a scroll chuck with a reverse "Chucking Alignment Adapter" which is inserted into the tail stock. The tail stock, with the bowl is brought forward to the vacuum cup almost touching and locked down to stabilize the bowl. Turn on the vacuum and advance the quill to the vacuum cup. After the bowl is sucked tight to the vacuum cup loosen the scroll chuck and pull the tail stock. Turn the bottom.
When I turn the bottom I like to leave a small foot for the bowl to rest on, this creates a shadow under the lower edge of the bowl, makes for a nicer presentation.