[JMay]

These Vac form units are built down to a price, and one of the cost cutting measures, is that here is no thermostat on the heater so it heats up and up and up...

In use, I form one sheet then allow the vac former to cool down before I do the next one, that way you can use a stop watch to time pre-heat of the heater then the actual plastic heating so the settings are then constant and therefore repeatable, otherwise the heat time shortens dramatically and burns the sheet. 

   

The plus point is that it will within the frame limitations and material etc create usable vac forms as above driver & windscreen. 

Cheers
            John