Well after a bit of delay, here is the next part of the build. The z axis, although made up of only a few bits, was one of the fiddly-est parts of the build. Here you can see one of the z axis threaded rods in its bearing assembly.
The underside of the assembly has a cog on that is rotated by the z axis belt, this ensures that both z rods rotated at exactly the same rate. Tightening the belt so that it was tight enough that each step from the stepper motor produced a movement in the z axis but loose enough that the stepper ran smoothly was frankly a pain in the arse. I think a different tensioning mechanism would be beneficial.
However once the z axis is done the only thing remaining is to mount the x axis. But before I do that here are a few pics of the frame so far.
The next step took a while, basically the x axis needed to be fitted. This involved loosening a few bolts, the z axis guide bars, z threaded rods/gear assemblies, sliding the x axis on, screwing the threaded rods into the trapped nuts (in the x axis), tightening everything and fitting the belt. All in all it took quite a while to get it to the point that the x axis was level and z axis would move up and down smoothly and easily. Here are a few shots of it with x axis fitted (if the x axis motor looks the wrong way up then that's because it is! I was testing an idea at the time of the photos).
Since it's rather late I will save the photos of the finished mendel for another day, time for a nice cup of tea. How quintessentially british!