the Z access can only go up ward cannot go down ward. I disassembly the Z access and reassemble it again. What I find out the T8 clamp ACME nut is extremely loose that cause the problem.(By the way I recently purchase a mk2 48x30 long mill ) problem need help. i try to attached video of the problem because I am a new user I cannot upload the video. I hope, I granted permission to upload this video.