I'm trying to figure out how to tighten/adjust the Z Axis Gibs on my vertical CNC Milling machine. I have a decent understanding of how Gib adjustment systems work on other machines, but this one is throwing me for a loop. It has 2 slides. Each slide has an upper and lower Gib making 4 Gibs in total for the Z Axis. I don't have the manual for this machine but it's a 1982 Pratt & Whitney TriMac V weighing 16,000 lbs. It's larger than a Bridgeport with a Fanuc 6 control system.

Originally I thought it had 1 long Gib in each side, but when I started pulling the upper right Gib upwards, the bottom Gib didn't move. They were independent of each other. I'm not sure which direction to go to tighten them. Is there a standard machining practice for this? Does anyone know which way is tighter/looser? I thought I could just tighten it up to the point of the Axis having a hard time moving (watching the Z Drive DC amps), but after tightening the set screw the all the way to the last thread of the bolt (about 4-6 full turns for each Gib) the Z Axis seems to slide up and down with ease still. The surface finishes of parts run on the machine have not improved either.

Basically the set screw drives the Gib in, and the other bolt pulls the Gib out. If the set screw is backed off, then you can use the bolt to pull the Gib out. If the bolt is loosened, then you can use the set screw to drive the Gib in. I just don't know if "IN" is tighter or looser.

I assumed that pulling the upper Gib upwards, and the lower Gib downwards would make the Gibs come completely out as I don't see how you could install them any other way. So I assume pulling them outwards is loosening them from the Z Axis. But After going inwards about 4-6 full turns on both the upper and lower Gib to try and tighten it up I have not noticed anything different. This all started when I noticed the right side slide was dry and I wasn't going through much Way Lube. The Z Axis would actually tip to the left enough I could visually see it every time Z went up. The oil metering ports were clogged, so I replaced them all. Now I get plenty of oil on the slides and the Z Axis isn't dragging or moving visually any more, but I still get pretty severe steps (.005") in my parts when going back and forth with the face mill. I don't think I tightened the Z Axis Gibs at all but I am out of threads. Is it possible the Gibs are worn out? Maybe the screws/bolts are too short? Maybe I don't understand what I am doing?

This has been a project machine for years so i am not afraid to dig into it and try things out. Thank you for the help

Benjamin,
Barch Designs