440 Z Axis Gib Adjustment... What Gibbs?!?!

Please forgive the pun. Since I received my 440 a few months ago, I’ve been having some issues with the Z axis. At first, the Z axis would stall at the top of the travel (towards the limit switch) when rapiding at high speed. I performed a gib adjustment on the Z axis, per the manual, thinking that was the issue. A slight improvement but the issue would still intermittently happen… so I reached out to Tormach and the tech suggested relubricating the ball screw. That did the trick! After testing the gib adjustment and newly lubricated ball screw, the lost motion measured at 0.0008", bang-on according to the manual. However, I’m realizing I only tested this towards the top of the machine’s travel (I used to have a vise on the table).

Now that I’m moving towards using the SMW mod vises, which bring the machine way further down in its travel, I’ve noticed the Z axis sagging/falling down when the machine is off. It won’t do this at the top of the travel, only towards the middle and bottom (essentially getting worse progressively towards the bottom of the travel). So I did a test… I adjusted the gib at the middle-bottom of the Z axis travel to the point where the machine stopped sagging downwards. I then performed a fine gib adjustment per the manual, with the Z axis in the same spot. I then moved the Z axis towards the top of the travel and measured lost motion – almost 0.005"! of lost motion. Yikes!

This tells me that the pressure of the gib is varying throughout the Z travel, with higher pressure towards the top of the travel and lower pressure towards the bottom. Am I correct in my assumption? If so, what can I do about this?

I did, using a 123 block and a 0.0005" indicator, verify that the machine’s Z axis is perpendicular to the X and Y plane without any noticeable error over the 3" block length. The only thing that’s out of spec is perpendicularity with X and Y, with a significant amount of error (0.0035" over 5"), but I figure we can tackle that after figuring out the Z axis situation (maybe they’re related).

The machine has only been used to cut aluminum and has never seen a hard crash (the worst I’ve done is snap an extended length 1/4" end mill from slotting too aggressively).

Just a note for anyone coming along in the future, you can expect to see a small amount of variability in lost motion depending on the axis position, but the level of that variability should not be in the thousandths range that Andrew is describing here. After working with Andrew in a tech support case we came to the conclusion that the measurements that Andrew had were unacceptably large and his machine slipped through our QC checks so we began the process to begin replacing his machine.

Thank you,

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