Sorry if someone has already done this, but here is my automatic pottery maker:
Its primary components consist of two turntables, two block dispensers, and a block detector.
The block dispenser at the top of the image contains clay blocks only. The block detector on the right is connected to this block dispenser with redstone so that when the dispenser places a clay block on the turntable in front of it, it stays on as long as there is a block or clay balls on the turntable.
The block dispenser on the left hand side of the image contains the desired pottery item in one of its inventory spaces and full stacks of cobblestone in the remaining inventory slots.
The turntable on the left hand side of the image sends pulses to both dispensers.
With this setup, the following actions occur:
1) The top dispenser dispenses a clay block on the turntable. The detector block detects this and keeps the dispenser powered.
2) The clay block begins its transformation into the desired pottery item. During this time, both dispensers are being powered on and off via the turntable set up on the left; but nothing happens since the top dispenser is always on and the left dispenser can't eject items (as there is a block in the way) nor can it suck in an item (since there is not a valid block to suck in).
3) Once the clay is transformed into the desired pottery item the dispenser on the left sucks it in after it receives its next pulse. There are clay balls on the turntable now so the top dispenser remains powered. When the left dispenser receives the next pulse, it places a cobblestone block and sucks it back in. This clears the clay balls that have accumulated, storing them in the hopper at the bottom of the image. The detector block shuts off and the dispenser on the top shuts off.
4) The cycle repeats.
The turntables are at setting two, and with the repeaters having the delays shown in the image, the machine works very nicely. Blocks (I used glass here) have to be placed around the contraption so that the clay balls are forced to be either on top of the spinning pottery or on the pottery's turntable.
I hope the explanation above is clear.
(I can't figure out how to place the image properly. Can someone help me here?)