Zero not staying true

Having a problem with the zero after it has been set. Once it is set and I run the program it run fine it isn’t until load the next piece to be cut do I notice the zero is the same anymore.

Usually this is caused by insufficient Z-axis belt tension, or a loose pulley set screw. For the former, think guitar string tight (but careful not to bend the motor shaft), for the latter please see:

Checked that and they are tight this has been this way since day one just thought it was the way the XXL ran.

How far off is it? If it’s just a touch, that’s probably just variation in material from sample to sample.

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By any chance do you have a dust boot that moves with the Z? I had an issue of Z slip because my dust boot would foul on deeper plunges. I went through the whole gamut of trying to test different things, including the fact that my garage was about 28F degrees at the time, thought maybe the belts were hardening. Anyways, if you’ve checked set screws, checked belt tension, check V-wheel adjustment, and the only thing left is a dust boot that moves with Z, might be worth a try? I considered trimming the dust boot bristles to thin them out, but in the end went with a Suckit boot and that issue went away.


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It is off about .500 to the left side of the zero

No I am not useing an dust boot and I have check the belts and the screws and they are both tight.

as in 1/2"? or .5 mm?

It is off 1/2" inch from the zero

oof. That’s definitely some sort of belt slip or step skip.

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After checking again I have lost two of my set screws so I will be down until I get some ordered thank to everyone that responded.

Get rid of those PITA set screws and replace them with 10 mm long cap screws. You’ll thank my later:


what’s the diameter of the screws

The community has notes on this sort of thing at: Shapeoko CNC Router, Rigid, Accurate, Reliable, and Affordable.

(pulley set screws (2 ea.) are M3, ~4.75mm o.a.l.)

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