For this post I make a bowl with a natural edge using a maple leaf with large leaves ( Acer macrophyllum ). The first step is to attach the faceplate to the front of the bowl; these natural side edges will always have an uneven surface to one degree or another. Slide some pads under the faceplate to align the faceplate to the bottom of the pivot block. The big trick here is to use long screws that go through the gaskets and well into the wood, the picture shows the screws and gaskets of the 3-inch wood. As an additional security measure, maintain a turn with tail sealing using a live center, the 60-degree cone works well.
During the rough phase of rotation, create a nozzle for scrolling; I like the recessed tail about 3/8 inch. Before removing the faceplate, make sure that the spiral cartridge is tightened inside the tail of the pigeons. Remove the faceplate, rotate the bowl and attach it to the spiral chuck; again supporting tail stock and lively center.
Turn the inside of the bowl, leaving about 1 inch of thickness along the sides and bottom. The center post can be removed with Forster bit , Clean the bottom and set aside to dry the wood.
The next step is after the wood is unloaded to a moisture content of about 12%. Complete the bowl rotation to the final shape and thickness of your choice, sand up to 250 grit. Put one coat of finish on the bow to protect the wood from stains (fingerprints) and discoloration.
Ready to turn the bottom, I use a vacuum cup to hold the bowl while the bottom is turned, I use it with a 6-inch vacuum cup with extension. You will need a vacuum generator, a sensor, and a valve to control the amount of vacuum. In round numbers, 1 inch of vacuum is 0.5 pounds. pressure. A 6-inch vacuum cup has a surface area of about 28 square inches. 26 inches in vacuum; 0.5 pounds per inch in vacuum equals 13 pounds times 28 square inches equivalent to about 364 pounds of holding force per bowl; it will work if you don't go fast or catch a chisel; this will move the cup from the center.
Lift the cartridge to the bottom of the bowl and attach the adapter for reverse bending to the cartridge and place in the tail section. Advance the bowl to within 1/4 inch from the vacuum cup and fasten the tail rod on the lathe tray, turn on the vacuum to 10 inches of vacuum and slide the pen to contact the vacuum cup, see the vacuum gauge, the inches of vacuum will increase when the bowl contacts vacuum bowl.
The bowl will always be a little center, perhaps this is normal; it will not be noticeable. Be sure and do not touch the finished surface with the tool. Turn the bottom part, sand and apply the end.
The finished bowl, notice how it is configured slightly, rather than flat on the table, adds a little depth to your design.
