Haas VF-3 Z height home issues

Dennisprototype said:

Hey guys, I've been a lurker for some years now and have gotten some great information from this site and its users. Currently I have a 1997 Haas VF-3 that changes its home height on every startup. I use a manual probe to measure a 2-4-6 block off the table as a z reference when setting work coordinates. I noticed that I couldn't just fire up the machine and take off machining parts, the z height coordinates would always be a little different every startup. No big deal it wasnt off by much, maybe a few tenths sometimes, sometimes a few thou. I began measuring and writing down the new reference on every startup to combat the issue. Well this last week on every start up the machine slowly drifted off in Z far enough that it began to affect the umbrella tool changer, not enough for a crash but enough for it to sound rough, definitely don't want that to keep happening. are their any simple things I can check to help my z origin or home more repeatable on startup? Is there a limit switch I can clean or replace possible? Maybe a loose servo coupling? Any help is appreciated.

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ewlsey said:

I doubt it's the switch. The switch just tells the control to look for the index pulse on the encoder. If the switch was loose, the position would be off by a factor of one full turn of the screw.

Have you tested for backlash? It certainly sounds like a loose servo coupling or thrust bearing or ball nut or something. I don't think the encoder can be loose, but I suppose anything is possible.

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