It's all in an attempt to get rigidity in the head. I wanted to have two Y rails/carriages, separated by a distance in the Z direction, to provide rigidity against the Z rail flexing. I wanted to have just one lower carriage, back to back with one of the Z carriages, but then there's no way to attach them both to the plate, because you can't get to the bolt holes of one when the other is in place.

So I ended up with the slight extravagance of two lower Y carriages, and the lower of the two Z carriages, all in a line as close together as possible at the lower end of the bracket. Since I had a spare carriage, I thought I might as well use it. Then there is the top carriage, providing a brace and incidentally holding the other end of the driving plate.

I'm open to suggestions though. My main intention is to make it as rigid as possible, which hopefully would make a good foundation for any further improvements in future.

Cheers,

Tony