Z Limit Switch Fault at Program Start

Just got my xyyz cnc router table set up and running.  Top of z is 0 maximum. Machine homes to the top with shared limit/home switch. I tried an air test of the linuxcnc default program and it started successfully, but doesn't have a G0 Z0 command. Throw in my my program from fusion 360, simple face mill operation of some mdf. When I start an air test I get z exceeds machine limits error that I can ignore. If I ignore it, machine moves to Z0, the top, and then gives me a limit fault for the axis. 

Do I need to edit the post processor to send to Z5 or did I mess up my configuration somewhere?

In fusion for the the z kinematics, I have z minimum set to -152 and max to 0. When viewing the program in the GUI I can't see that the program exceeds the work area, and it shouldn't... it's only a 10x10in face operation on a 2x3ft table. I'm not even sure if these 2 issues are directly related, but any suggestions on what to check or look at? 

I have a 7i96s board, and I'm running a prerelease 2.9 when I originally set the computer up last spring. At the time I was struggling to get it working since I wanted to get probe basic running. Turned out things were being updated daily and scripts were missing as I was in the middle of the project, lol. So not sure if there is a bug that was addressed that might be related, and kind of hoping I don't need to go through the install again. Just to clarify though, I'm currently using axis as I steadily go through testing the machine.

I've shared the program, along with hal and ini files below. Yes, the machine's name is "Moby Dick" as you'll see in the file name lol. It was a few frustrating weeks getting the computer set up the first time.

I think you need to add a HOME_OFFSET  of say 0.5mm to move the  home position off the limit switch. I think what is happening now is the home/limit switch is set during homing and when it comes out of homing it immediately triggers a limit switch error.

You need to jog  away from the machine limits and touch off X &Y before running your program. There needs to be enough room for the  width of the tool between the work piece and the machine limits. 

It is probably worth backing up your linuxcnc folder and installing V 2.9.2 as it comes with the latest 12.4 version of Debian  and also has the repositories installed. You might also look at qtdragon as a nice touch friendly GUI that is well documented on the linuxcnc docs pags.

Z offset of 0.5mm might not be enough, so try 2 or 3mm.
Depending on the home final velocity, the switch will trigger and since it takes a bit to stop, it will probably need more than 0.5mm to back of. The default home final velocity is 0 so it is the max for a given joint.
Usually i set final velocity to 10 on my big machines, that is 600mm/m.

Ok, I think you guys are definitely correct, and after looking at the homing doc again I just wanted to clarify for myself what linuxcnc is doing.

Say Z max physical travel is 152mm, 0 being at the top. I have HOME set to -5 as the final home position, but this is only the position and isn't creating a soft limit. So if I set HOME_OFFSET to -2mm for example, then -2mm physical location is now stored as machine 0 in G53 and is the machine soft limit. Then a G0 Z0 command would in fact be 2mm away from the shared limit switch physically. 

Does HOME make the move after HOME_OFFSET, thus it would actually be 7mm away from the end of travel?

I found a difference in the ini files on the two configurations (here the step_scale was set to 160 on my old pc (however pncconf showed 200) and on the raspi it was set to 200) 
I changed the ini file manually now the same distance movement is happening on both configs - well, I don't why, but it looks like this caused the different although PNCConf showed something different.

The above comments are also very helpful for me to understand what LinuxCNC is doing.

Many thx