Belt-less 3D Printer ?

Hi.

I've not read every post on the site but I've yet to find a 3D printer design that does not use drive belts.
Is there a reason for this?
Anyway, I've designed a printer that only uses acme threaded rods for all of the movement.
What are the flaws with my design?

Your feedback would be much appreciated.

Bob

View attachment 13909
View attachment 13910