I see what you mean about it moving away from wheels, but that would take a lot more force and I don't see how it would happen. The workpiece can only push from the very bottom.

The supported rail was my plan, but I seen the guy on YouTube done it and it didn't help at all. Maybe with the fat backplate though. The way the ballscrew is attached to the bearings just now make it look like a big job. I'll need to have a good think how to do it though.

BTW, I'm still using the machine in between mods. I did specifically buy it with intention of modding it and learning. I knew the weaknesses when I bought it, if anything it was a lot better than I'd expected. I didn't get disappointed. It's a hobby machine. I'm hobbying.