When I first put together my 2418 Mini CNC machine, the Z-axis would work it’s way free and crash into the work piece. I couldn’t get the grub screws on the blue coupler tight enough. The leadscrew would drop straight out.

Picture of the z-axis on a 2418 CNC mill with annotations of how it can fail.

I had a spare 604 bearing lazing about the place, and it turned out to be a perfect fit for the hole in the bottom of the x-carriage. It needed a fair knock to get it installed, but the tight friction fit has given the z-axis that extra support. The leadscrew hasn’t fallen out since (~50 hours of milling).

Where to install a 604 bearing on a 2418 CNC mill to stop z-axis crashes.