For this post I am making a Natural Edge Bowl using Big Leaf Maple (Acer macrophyllum). First step is to attach a faceplate to front of the bowl; these natural edge bowls will always have an uneven surface to one degree or another. Slip some shims under the faceplate to level the faceplate to bottom of the turning block. The big trick here is to use long screws that will go through the shims and well into the wood, picture shows 3 inch wood screws and shims. As an added safety measure support the turning with the tail stock using a live center, 60 degree cone works well.
During the rough turning phase create a spigot for the scroll chuck; I like a recessed dove tail of about 3/8 inch deep. Before you remove the faceplate make sure that the scroll chuck will tighten within the dove tail. Remove the faceplate, turn the bowl around and attach to the scroll chuck; again supporting with the tail stock and live center.
Turn out the inside of the bowl leaving about 1 inch of thickness all around sides and bottom. The center post can be removed with a Forstner Bit. Clean up the bottom and set aside for the wood to dry.
Next step after the wood has dried to moisture content of about 12%. Finish turning the bowl to the final shape and thickness of your choice, sand to 250 grit. Put one coat of finish on the bowl to protect the wood from stains (finger prints) and discoloring.
Ready to turn the bottom, I use a vacuum cup to hold the bowl while the bottom is turned, I use a with a 6 inch vacuum cup with an extension. You will need a vacuum generator, gauge and valve to control the amount of vacuum. In round numbers 1 inch of vacuum equals 0.5 lbs. of pressure. A 6 inch vacuum cup has about 28 square inches of surface area. 26 inches of vacuum times 0.5 lb. per inch of vacuum equals 13 lbs times 28 square inches equals about 364 lbs of holding force on the bowl; this will work unless you go to fast or snag a chisel; this will move the bowl off center.
Reattach the chuck to the bottom of the bowl and attach a Reverse Chucking Alignment Adapter to chuck and place in the tail stock. Advance bowl to within about a 1/4" of the vacuum cup and lock the tail stock to the lathe bed, Turn on the vacuum up to about 10 inches of vacuum and advance the quill to contact the vacuum cup watch the vacuum gauge, the inches of vacuum will increase when the bowl is in contact with the vacuum cup. Loosen the chuck and withdraw the tail stock, adjust the vacuum to what you want, to much vacuum can mark the bowl.
The bowl will always be slightly of center maybe this is OK; it won't be noticeable. Be sure and don't touch your finished surface with a tool. Turn the bottom, sand and apply finish.
The finished bowl, notice how it sets up a little and not flat on the table, adds a little depth to you project.
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