Throwing plates is one of the most difficult processes to master as a potter. Being able to throw out without letting a plate flop with the centripetal force is challenging. Also, making the base thick enough to be cut off the boad is very important. Lastly, during drying, plates have a tendency to crack or split because of their uneven nature. Overall, this results in many many failures and plates lost to the reclaim bin. Here, I've been working on my plate throwing and letting them tell me what to do. In a sense, I feel when I should stop throwing. The moment a plate will flop is quick to notice, and that is when I make the final pull. Because I'm still learning this process myself, my plates err on the thick side. However, this can always be corrected in trimming. If you are also trying to throw plates, my advice would be to compress the bottom as much as possible. Then pull quickly. The less time the plate is spinning, the less likely it will flop down. Also, the slower your wheel, the easier it will be to control. In conclusion, plates are a challenge worth approching and defeating.