What causes lost zeros?

[Cadefoster84 (Chris H)]

I was running some tests in a clear cast acrylic trying to improve my carve quality and had to stop my shapeoko 4 pro mid job while i had to run out for a minute. When i hit stop my z axis raised and started bounceing off the z limit switch and CM motion through up a "machine in unexpected state error And crashed. Culprit was a loose cinnection so i sorted that and loaded my file back up expecting CM to have remembered my zeroes. When i started the job, my carvinng was slightly off off where it sould be. Any thoughts as to why that happened? Im confident my stock didnt move, working holding with painters tape and glue.

[LiamN (Liam Newcombe)]

The machine doesn’t have sensors to tell it the position of each axis, only home switches to tell it when it is at ‘machine zero’

When it starts up and you home the machine, it moves until it triggers the home switches on each axis and sets machine x=0, y=0, z=0.

From there it then steps in little (about 0.025mm) steps from that known position and just remembers how many steps it’s taken to know where it is. If you crash the machine and cause it to lose steps, such as when it ran into the limit of Z travel, the machine doesn’t know how many steps it’s missed and now the machine z=0 is wrong.

The workpiece x=0, y=0, z=0 is set when you go and set zero somewhere in the work space, the machine just remembers what the machine x=280, y=540, z=40 or whatever numbers were when you said “workpiece zero”.

So after crashing the machine you need to re-initialise the machine to get machine zero and then it’s worth checking the workpiece zero too.

HTH

[gdon_2003 (Guy Donham)]

The proximity switches are pretty accurate but not perfect. So after every power cycle and homing cycle you could be off a few thousands of an inch. Now if you are off more than a few thousands then as @LiamN indicated you would need to completely power cycle and rehome. Then before starting a job you can go into Jog and use Rapid positions and find your X and Y origin that was set the last time you physically set them with either a BitZero or any manual method you chose. Then you can use the Z+6MM to see if your Z is set to 6MM above your last Z origin. Be very careful because you can crash into your material if it is off or if you use bottom of material you would crash into your material. So to check the Z+6mm jog off the material to check Z zero.