Throw a bottomless cylinder to a width and height appropriate for the kind of work you will be trimming. It is often desirable to flare the top so that several different shapes will fit in the chuck. Make sure the chuck is perfectly round. Allow the chuck to dry evenly so it does not go out of round, and fire in your normal bisque firing.
This is a closed-cell foam material that is used to make wet suits and a multitude of other items. A quick online search will turn up tons of sources. You will want to glue the neoprene in place on the chuck, and some manufacturers produce adhesive-backed neoprene for making gaskets. Otherwise, you can use a construction adhesive or caulk that will remain somewhat flexible.
Really, this can be any bat with holes for bat pins. You could make a superchuck for a wheel head without bat pins, but you would then need to throw a pad to adhere the bat, and you would need to center it. We suggest you skip the bat if you don’t work with bat pins; just center the chuck with neoprene attached and attach it with lugs of clay, as you would with a normal chuck. It’s not the same, but you still get the advantage of the grippy neoprene.
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You can use the five-minute epoxy that comes in a double-barrel plunger, but an epoxy with a longer working time will allow you to carefully set and center the chuck on the bat. This will be especially useful for larger chucks. There are several kinds of epoxy available, from two-part paste epoxy like PC-7 to puttys that are mixed by kneading. Most are available at hardware stores and home centers. Mix the epoxy according to the label directions.
Putting It All Together
Attach the bat to the wheel head and center the chuck on the wheel head. Mark the location of the chuck by drawing a line on opposites sides of the chuck down the side and out onto the bat. Flip the chuck over on the wheel head so the base is facing up. Mix the amount of epoxy you will need and apply it to the base of the chuck. Flip it over and reposition the chuck according to the marks you made. Press the chuck down firmly onto the bat so it is nice and level. This will force extra epoxy out of the join and allow the chuck to seat level with the bat. You’ll want to spin the wheel slowly to recenter the chuck. These will be small adjustments, since the marks help you place it mostly on center, but you want to be sure that the top end of the chuck is absolutely centered.