I seldom use a chuck, and never use them to turn calls. While many people use a chuck to turn their pots, I prefer to use the faceplate that came with my lathe. I am on my 3rd Jet mini in the past 12 years and am still using the faceplate that came with the first one I bought. I use a 1/4" acrylic waste block between my faceplate and my pot call blank. I use 4 screws that extend about 1/8" into my call blank to hold it to the faceplate. MANY times in the earlier years I would turn down to the screws. That tell-tale sound and feel of the end of the screws against my gouge let me know when I had gone too deep. Rough on the cutting edge of a tool...
I learned to stop and check the depth of my cut in the pot turning process with more frequency. I can see the depth of the screw through the 1/8" pilot holes drilled for my sound holes to gauge the correct depth of cut/thickness of the pot bottom.
I share all of this to let you know, you don't HAVE to have a chuck to turn pot calls. Different folks use different methods with good results for their pot designs. I have a Nova 4 jaw chuck that serves as a weight to apply pressure while gluing call surfaces in. While it has turned a lot of other items from tube calls to coffee scoops to ferro rod handles, I really couldn't recommend the model I have, as it never really had good "centricity". From the first use it seemed to be a hair off center, which caused turned items to have some variance in wall thickness when turning tubes or drilling stock.
