Machine Zero Hell

[LBayZG]

Just reporting this issue so that there is a mention of it.
I have since resolved the problem. So no official reply is requested.

Last Wednesday, I managed to use my miniature mill for the first time. Worked great.

The next day - Somehow - my UCCNC mill settled on the assumption that machine zero was supposed to be 50 inches.
X(0) - 50 inch.
Y(0) - 50 inch.
Z(0) - 50 inch.

My first indication that something was wrong was when my 'Spot Drill' plowed some 3/4" inches through my work and into my mounting plate. Thankfully it did not reach the mill table itself.

It turns out that my Fusion 360 post files always start out with these two lines. (They worked fine on Wednesday.)

G90
G0 G53 Z0.

So - thinking that it's Z axis was positioned at +50 inches - the tool abruptly took a plunge at high speed - looking for 0.
The funny thing is - it kept going down ,even though the 'work coordinates' reached negative numbers.

Numerous applications of the 'GO HOME' button, which should have reset the machine-zero coordinates just left them at 50,50,50.
And yes, I have 'home switches' for all three axis.

In the end, I solved the problem by performing a fresh install of the latest UCCNC software (ver 1.2104).

After the re-install, the machine-zero coordinates behaved rationally. HOME-ALL now sets the machine co-ords to 0,0,0.

[dezsoe]

The funny thing is - it kept going down ,even though the 'work coordinates' reached negative numbers.

There's no funny thing: G0 G53 Z0 tells your machine to go to Z0 in machine coordinates. The DROs show the work coordinates, unless you switch to machine coords. Do you have home sensors? Are you homing your machine before any work? When you shut down UCCNC, it saves your mach coords. If you don't home the axes on next startup, they may be in wrong position,

[cncdrive]

That is how G53 works.
If you check the Offsets page you see that it is a equation:

Current coordinates = Machine coordiantes - Offsets

Now if your home coordinate is 50 and you have an offset of 50 so the Z=0 in the current coordinate system (axis zeroed with zero button on the home position) then a G53 G0 Z0 will move your axis to Z=-50 in the current coordinate system, so the endpoint of the move in the current coord system will be Z=-50 and the machine coord will be 0 as the offset is 50.
This is because G53 is linear movement in machine coordinates and so it moves a distance to make the machine coordinates coordinate the programmed value and not the current coord.
I suggest you read up on the G53 code to better understand how it works.

And I'm not sure what do you mean by "GO HOME" button. If you ment goto Zero or the Home all,
but non of them are always zeroing machine coordinates.
The gotoZero button goes to zero in the current coordinate system and so if there is offset then it will not zero the machine coord.
And the Home all button will set the machine coordinates to the values of the "write offset on homing" fields, so it only resets the machine coord to 0 if that field is 0.

[LBayZG]

Sorry - my bad. What's in my head is (sometimes) not what gets written.

Sorry, I wrote earlier that I pressed the 'go home' button, but I meant to say "HOME ALL".

To dezsoe - yes I have limit switches, and yes they are configured correctly. Each axis would seek to and then back off from the limit position.

I am (obviously) a newbie. But I am able to look up g-codes on the web.

When I realized that the G0 G53 Z0 line was sending my mill's head to machine coordinate Z = 0.0, I began to suspect that something was drastically wrong with the values for machine zero itself.

Here is the problem:
When I press the "HOME ALL" button, the machine would travel to the limit switches, and then set the MACHINE COORDIANTE for each axis to 50.

That is what makes no sense. How is it possible for 'HOME ALL' and limit switches to set the machine coordinates to such a value?

[ger21]

Set the Write Offset on Homing to 0 on the Axes setup screens.

[LBayZG]

Set the Write Offset on Homing to 0 on the Axes setup screens.

Thanks for that information. It explains all. I hope to never repeat that mistake again.

Sorry I took so long to get back with a confirmation.
All is well now.