Just in case you all thought that I'd gotten bored and given up, well I'm still here and beavering away, I just haven't got anything solid to show you. Progress is still good, but I just had a little bit of a two steps back to make one step forward situation to get through before starting the next unit.
After having a good play with the machine as it stood in the last photo, I came to the conclusion that although the gear work was all fine, the frames were just not good enough.
Unfortunately, when I first fitted the gearing to the frame work, I got myself very confused as to which gear went where and so drilled a few holes that should never have been drilled. I could fill these, but they would always be visible, and if the jobs worth doing...
More important than that though, I also didn't leave enough material to fit decent size spacer poles, my preference is for 6 mm wooden dowels, rather than the 3mm metal rods currently fitted which was all I had room for at the time - changing them will make fixing everything together so much easier.
Lastly, the purpose of the gear teeth running around the outside of the bottom frame is to provide the main input drive for the entire machine via the winding handle. I've decided to lose this in favour of a smaller gear that will be driven by a worm gear - both to be fitted later - so all three new frames can have smooth edges.
So while it's still at a relatively early stage in the build I have opted to cut three new frames and re-fit the existing gearing to them instead, it's a bit of re-work that's worth doing I think.
I'll hopefully have this all finished in the next day or two, and this time I'm staining and varnishing the bits that require it, as well as fixing all the gearing in properly so that I'll end up with the first properly finished unit.
That's the plan anyhow...

Slightly beefier frame design before cutting.