@dwuk Hi David,
I did a quick sketch to show you the cam concept. I can't upload a photo, so I put the link below. You should erase the spaces.
I tried to use arrows to explain which part is which.
You should add a mechanical switch to limit the lower Z position of the extruder. When the extruder reaches the lower Z limit, the spring should have slight tension—this will likely provide sufficient accuracy.
Additionally, if you add a screw to adjust the lower Z limit, you can fine-tune the adjustment to ensure both extruders are on the same plane.
https :// freeimage . host / i/2Qk9jcl