The quantity of sample placed into the film maker kit before melting and pressing is a major factor in the consistent thickness of film being produced. In addition the sample type, the load and the time that the load is applied to the sample (when the sample is cooling down) will all determine the overall thickness of the film to be produced.
As an example, two sample discs of a PTFE type material were prepared in an Atlas™ High Temperature Film Maker Accessory P/N GS15800. A temperature of 305°C was needed to melt the samples and they were compressed at a 1 ton load. The intention was to produce 0.1mm and 0.25mm thick films, therefore the 0.1mm spacing ring was used for one sample and the 0.25mm spacing ring for the other. Sufficient sample was placed into the kit so that on melting there was excess sample around the edge of the disc (acceptable overspill) for both thickness of discs. When the samples had cooled, their thicknesses were measured using an electronic micrometer.
Interestingly, the 0.1mm spacing ring produced a 0.07mm thickness film and the 0.25mm spacing ring produced a 0.18mm thickness film. These values are surprising because it was expected to produce the MINIMUM thickness allowable from the ring value chosen i.e. a 0.1mm film and a 0.25mm film. However, it is the nature of the PTFE sample to “shrink” on cooling and comparison of the rates of shrinkage shows a reduction of 0.1mm to 0.07mm equates with a reduction from 0.25mm to 0.18mm. (A factor of 0.7).