Y is only up on the screen. It’s away from you in the workspace.
If the whole gantry stops moving in one direction but moves fine in the other direction, you may find that the mechanism is binding. Check to see if the gantry is a little bit too diagonal compared to the rest of the frame of the Sculpfun. A carpenters square is a great tool for checking.
thanks for your reply. i have try. it can move left and right only. carpenter square only can make a straight line because it bounds back when go upward and downward