Calculations were then done to work out the diameter differences needed of the shaft to the coupling bore (interference). We wanted to ensure that the correct pressure was generated between the shaft and the coupling to end up with the right figure of force.

We then assessed the coefficient expansion rate of the materials to decide how much heat was needed to expand the coupling. Because it is made of high tensile steel, however, we could only heat it to a certain temperature. Going over that temperature would mean that the material would anneal and would then loose tensile and yield strength.

Unfortunately, with the amount of interference needed, we found that heating the coupling up to its maximum allowed temperature was not enough thermal expansion to create clearance to the shaft to be able to fit it. So we had to take another step to achieve enough clearance to drop the shaft in.

The only option was to freeze the shaft with liquid nitrogen (-195.79 °C) in order to shrink it. We then heated the coupling to expand it, and with both of these methods combined, managed to slot the shaft into the coupling. Once the shaft and coupling both reached ambient temperature, the pressure generated between created the right amount of friction to perform the task.

Now the couplings and shaft were one part, the dummy shaft was then placed back in the machine for final machining.