PC is somewhat of a thermal insulator so the alloy has to get to proper temp. to get the 'cure' on the alloy surface. Just because the PC flows doesn't not mean it is near cure temp. Adding thermal mass to the oven just means it takes longer for the temp to increase although it does tend to heat more evenly. Just compensates for heat loss when opening the door. Heat is like water, when it leaks you have to replace it.curing time starts when the substrate reaches the required temperature.