When making a change to a plastics process, it should always be large enough to make a noticable change. It is often difficult or impossible to differentiate between normal variation and the effects of a small change.
Question: Why do you advise against making small gradual adjustments?
My Response: Plastics materials introduce an inherent degree of variability to the process. Additionally, aspects such as temperature, humidity, and equipment wear are always fluctuating over time. For this reason, you will see always see some amount of shot to shot variation in the process as well as process fluctuations. For example, if you increase the mold temperature 2° to adjust a dimension, any change you might see could easily be the result of normal process variation in a different parameter such as material viscosity. If the temperature was adjusted by 10° and the dimension did not change significantly, then you know with certainty that the mold temperature does or does not significantly affect this dimension.