The scale of the picture may be deceptive — the screw is 1/4″ thick. Two friends of mine have home-built CNC drill/mill machines with the same screw, so I know from experience that it’ll be adequate for my use. And anecdotally, I can’t resist the movement of the platform by hand.

Another consideration is that since this is inexpensive hardware-store all-thread, the threads have a V profile. For a larger machine and/or for cutting harder materials, I’d definitely use a leadscrew with Acme or square threads.

If I misunderstood your point, I love to hear more!

It looks to me that you have very thin screw so any resistance from the tool (when it hits the hard surface) will break the alignmen and can lock the screw. This kind of a design doesn’t save you from some backlash (even if you have this thick printer rod as a stabilizer) – this makes the carriage very sensitive to the rsistance from a work surface when the tool touches it. Be carefull here.