Anybody used these linear bearings before?

[irving2008]

Generally, for a conventional mill, X is left/right, Y is front/back and Z is up/down. for a moving gantry device, X is usually the gantry movement, Y is the cross-gantry movement and Z is still up/down.

You only need 2 carriages if the distance from the rail to the load point is more than twice the length of a carriage. For two rails the carriage length must be no less than 1/3 to 1/4 of half the distance between rails. So, for an A4 work area 300 x 210 approx the X-rails will be ~250 apart (unless its a moving bed in which case they can be closer together). therefore the carriage (bearing) must be at least 60 - 80 long, and since they aren't you will need 2 spaced at 75mm. The parts you need for that configuration of x-rails are 1 x NK-02-27-2,350 & 1 x NK-02-27-2,350 LLZ costing about £40 and they'll be good for 2y worth of continuous running with a 15kg gantry/router load running at 1.5m/min traverse speed...