Haas VF-3 Z height home issues
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  1. #1
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    Default Haas VF-3 Z height home issues

    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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    Quote Originally Posted by Dennisprototype View Post
    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.
    are you saying that every time you take it HOME your home position moves?
    sounds like your switch is loose.

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    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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    Quote Originally Posted by ewlsey View Post
    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.

    ment to say the dog. ie the part that trips the switch. as that part would be the only thing that would constantly move. the switch would just move back and forth. I believe that year haas still had them

    the coupler could be loose but I think you would see that problem in Z axis repeat ability when cutting parts (butt the head is pretty heavy.)
    my 40-20 fadal had a loose coupler and it mainly affected the z repeatability when cutting. homing wasnt an issue. you could also hear it in the peck drilling as well combined with bad thrust bearings.


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