I'm a newbie to hobby CNC but I've been using an ebay Chinese 3040 CNC for a few months now. Up until today I haven't had any problems. Today I noticed one of the Z axis linear bearings has somehow become pretty loose and slides up and down within the z-axis spindle mount.. This machine has a pair of LM12UU linear bearings on the Z axis that are basically press fit into a hole in the aluminum spindle clamp mount. It appears nothing holds the bearings in place except friction.

One of the linear bearings is so loose it actually slides up and down in the spindle mount with a little finger pressure. It also falls down due to gravity and vibration when the machine is cutting. When the loose bearing slides down it creates binding when the z axis goes to lower. The left bearing stays in place but the right bearing slides down. When the z-axis lowers and attempts cutting it binds, the Z-axis stalls out and blows the spindle fuse.

Has anyone experienced this issue? Since these bearings have a groove for a snap ring I was thinking I could remedy the bearing dropping down by installing a snap ring at the top of the bearing. Would this be a suitable solution or is the bearing loose because it is bad? The bearing sounds/feels fine when it slides along the shaft, the issue seems to be it slides too freely within the z-axis itself. Any input is greatly appreciated.