i bought one of these machines and after a couple of weeks my spindle mount (Z axis) had over 3mm of play in it. here's how i solved it.
First take the motor out, followed by the whole z axis mount complete (easiest to leave the lead screw in it as it won't get in the way)
ok with the whole z axis on your bench undo the z axis lead screw collar that attaches the servo to the lead screw and remove it followed by the four machine screws on the z axis servo and carefully lift it off.
now look on the bottom of the mount and you will see two small cross head machine screws holding the 8mm slide rails, take out the two screws.
now look under the four cream coloured spacers where the servo attached and you will see four recessed pozi head machine screws (to make life easier i bent at right angle an old slim pozi screwdriver to make undo these easier)
you only need to unscrew three of these as the servo mount can be turned so that you can slide the 8mm rails out, now unscrew the z axis lead screw if not done already.
you should now be able to remove the separate spindle/motor housing which has two cheap and nasty linear bearings in each side (8MM x 15MM x 24MM) these are way too short and allows for rapid wear due to the stress they take. now the depth of the holes where the linear bearings are located are actually 35MM.
carefully tap or press out the old linear bearings.
now with two plain holes waiting for new linear bearings you will want to get hold of 4 of this size 8MM x 15MM x 17MM (two for each side =34MM.
once you have your nice new 17MM long linear bearings go ahead and tap one in each end of the motor housing rail holes.
once the new bearings are fitted have a look on the top where the z axis lead screw would pass through and you will notice a circular recess 8MM X 15MM
I put three M8 steel washers in one at a time and super glued each one in while periodically inserting a piece of 8MM bar to keep the washers central until the superglue set. you will notice that the last washer you put in is perfectly flush with the mount surface and to make sure the washers never came out i screwed down a M5 steel washer so the it overlapped the M8 washer keeping it covered and secure..
now that's all done go ahead and put back the motor housing and slide the 8MM rails back in and secure with the screws you removed, then line up the servo mount and tighten the recessed pozi screws and check the cream pillars to make sure they don't spin and is tight, attach the servo motor and tighten the 4 machine screws.
put the z axis lead screw back in only far enough so you can attach the servo to lead screw aluminium collar and secure it via the tiny grub screws.
now go ahead and put the whole axis back on the machine and re align those rails. once all the rails are aligned and both X and Z axis are working ok go ahead and grab hold of the mount and see if there is any play in it....i guarantee you it will be solid with zero movement ........happy days :banana: