Agreed the z-axis wouldnt be.. but this is a 600mm screw... I didnt get it was the Z-axis anywhere...

Though pragmatically I agree with Gary, the coupler will ease some of it... though a typical Nema23 stepper is spec'd at a maximum axial force of 15N so although the coupler will compress out to take up some motion it will still transmit a significant force to the stepper shaft. Those wavy washers might not stay wavy for long! I'd consider putting the screw under slight tension at a lower temp to give some flexibility when/if the temp rises....