Problem- Question about control read out.....

[cnc Rookie]

Boss 6 readout......Here's what happens....after I run a program and the Z goes back to home it sometimes does not read 0 on the readout. It may leave it hang down .0005 or sometimes .001 from a total zero home move. If this happens, which isn't every time, just sometimes, all I have to do is switch to setup....step the Z down an inch and zero it out and it will then go to dead zero. It never leaves it hang down if I manually zero it out only after it has run a program. If I just ignore it sometimes it will go away and sometimes it will start to accumulate by .0005 at a time and start adding up so the next time it may hang down by .0015. It is never consistent and always zeros out when I do it manually so over the years I have just come to watch for it and check the readout before I run the next program. I've never checked but I assume in absolute mode it wouldn't make any difference as long as it is moving to where the readout says it should be(except for the home position). But I guess it could screw with things if I were running an incremental program....not really sure about this either?

My question is this......is there something I can do to fix this so that it will zero out every time it is done running. Would it be a mechanical or an electrical problem I would be chasing?
I talked to a couple others and they have never heard of this in a Boss control before so I thought I would check here.
It's just more of an annoyance than anything but if I can fix it I sure would like to.

Thanks
Dave

[arhctysv]

Dave:
Does the dial under the
Z axis motor misposition too
or is it just the readout?
If the display is off
then the problem would be
probably the control.
This is an open loop system
so the control has no way
of knowing whether z axis
made it home. You are the
feedback by looking at the
dial under the motor.
If it comes up short on the
display then the control is
telling it to be short for some
reason. I did have a problem
once where the decel switch
on Z axis caused Z axis to act
funny. You might try to replace
it. It is the second switch down
from the top under the Z axis
front cover. Usually is a roller
microswitch. If that doesn't
do it suspect a ZDI or ZCK
circuit board.
Rich
Arch City Service

[cnc Rookie]

Thanks Rich...
I'll have to check the dial and see what it says when this happens.
I thought also it may have something to do with the decel microswitch or the stop switch at the very top but then I thought if that were the case why would it zero out in manual mode every time and not leave the Z hanging (at least on the readout) when I hit the Z zero button?
I'll have to check and see how much a switch is and change it out if not too much.
It's one of those things that you sometimes wish it would just quit working so I would know and just be able to fix it.
(Careful what we wish for at times!)

Dave