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With the outside of the bowl shaped to your preferred profile, we need to configure the bottom of the bowl so that you can reattach it to the lathe. This will allow the removal of material from inside the container. This is called Reverse Chucking and a four jaw displacement chuck is used to clamp the bowl to its lathe with the inside of the bowl facing the tail. The bottom of the bowl has become flat and square to the lathe; turn on a tap about ½ inch high in the bottom of the bowl. I prefer to use a large diameter spigot and then create a recessed dovetail cutout in the spigot about 3/8-inch deep. The diameter of the dovetail should be within the travel range of your Scroll Chuck jaws. For heavy bowls I prefer the recessed dovetail; this method is stronger. Smaller bowls that you can flip with a smaller faucet and hold the outside of the faucet.
Remove the bowl from the lathe and remove the faceplate and place the chuck into the dovetail hole. Better way; is to attach the chuck to the bowl before connecting the chuck to the lathe, this ensures better alignment. Then connect the chuck to the head. If the chuck is not positioned correctly in the dovetail hole, the bowl will wobble. A slight wobble is fine because the container will readjust after it dries. The jaws are numbered on the offset mandrel; Mark the bottom of the bowl to correspond with one of the jaws so you can put it back in the same position after drying.
After the bowl has been attached to the scroll chuck and connected to the lathe head. Natural rim bowls have an uneven surface and will put a lot of stress on the chuck’s holding capacity when you start to turn the inside. For safety and to help support the bowl, use the glue as a support, the same procedure as in item 2.
Place banjo between bowl and cola stock; With the tool holder at the proper height, rotate the bowl by hand to ensure it can rotate freely. Using a bowl gouge and starting near the live center of the 60 degree cone, start carefully and slow down by cutting into the inside of the bowl, once you have some depth and even cut you can go faster. As you go further into the container, you will need to bring the tool holder closer to the surface of your work area. If any tool extends beyond the tool holder, it will cause a lot of vibration.
The distance a tool can extend beyond the tool holder is related to the size of the tool you are using, it is best to follow the manufacturer’s recommendations. Large diameter tools can extend beyond the tool holder than a small diameter tool; the same with the thickness.
The container should be dried after the material in the container has been removed; this will be discussed in the next article. The thickness should be about 1 inch thick, on the sides and bottom, except for the dovetail hole, which should be thicker. At this point, much of the weight has been removed and you can draw the tail. The spigot left inside the bowl can be removed using a Bowl Gouge or I prefer to use a large Forstner Bit. With a chuck mounted to the tail shank, you can advance the bit and remove the remaining wood; a horizontal drill. When the inside of the bowl is uniform; use the round tip scraper to smooth the inside of the container.
The attached link is a glossary of terminology for the lathe and associated tools; http://www.turningtools.co.uk/glossary/glossary.html