Homing / limits - the manual is misleading, possibly wrong

To be clearer my bet is you can trip the positive limit after homing but will be 3mm away from the negative limit.
And if you can trip a hard limit after homing, something is wrong.

so this works for me
but I have HOME_OFFSET = -3
when I set it to 3 I get a limit switch error during homing
I can do the full travel and it stops at the soft limit before it hits my end stop

it seams like setting the HOME_OFFSET = -3 is saying that the limit switch location is at -3 so it hits the switch homes to 1 then can never go below 0 because that is the hard limit negative of the machine

[JOINT_0]
AXIS = X
MIN_LIMIT = 0 (hard limit min)
MAX_LIMIT = 440 (hard limit max)
HOME = 0 (moves machine to this position after homing )
HOME_OFFSET = -3 (distance to offset machine coordinates by, sets machine 0 at that point)
HOME_SEARCH_VEL = -60 (search towards the min)
HOME_LATCH_VEL = 30 (latch toward positive and back)
HOME_SEQUENCE = 0
HOME_USE_INDEX = False
HOME_IGNORE_LIMITS = True

MIN_LIMIT = 0 (hard limit min)
MAX_LIMIT = 440 (hard limit max)

technically MIN_LIMIT and MAX_LIMIT set the soft limits not the hard limits.
Linuxcnc doesn't know anything about hard limits location, just to disable the amps.

I can do the full travel and it stops at the soft limit before it hits my end stop

You say end stops - I assume you mean limit switch.
It's hard for me to say why this still works without seeing everything.
The differences between switch trip point and measurement of actual t trip-to-trip travel vrs what is entered into linuxcnc could make this work satisfactory in practice. As I said 3mm isn't much.

it seams like setting the HOME_OFFSET = -3 is saying that the limit switch location is at -3 so it hits the switch homes to 1 then can never go below 0 because that is the hard limit negative of the machine

Well almost it hits the home switch tells linuxcnc this is -3 then moves to home position (0 from your post there)
meaning you are 3mm from your home/limit switch and your position is 0
meaning you will always be 3mm away from the home/limit switch when it stops at the soft limit, which you set at 0

To see what i mean set your HOME_OFFSET to something easy to see say -25mm
Then you I think you will see your operating limits have shifted 25mm away from one limit and 25mm past the other.

Chris

I guess to put it in perspective if it works for you then that's fine - my guess is your missing about 3mm of travel which doesn;t make much difference.

I was only trying to confirm that the docs are right and think how we could improve them. ( I in fact already added a little bi to the docs about machine assumtions that homing makes)

Chris

linuxcnc.org/docs/2.8/html/config/ini-homing.html#_prerequisite

yes, I am absolutely losing 3mm of travel with the way the config is

if I just have a home/min limit switch I had assumed (probably bad on my part) that I would not want to be able to get too close to the limit switch during travel, which means I need to "lose" some amount of travel. I looked at it as the overrun space.

the link is super helpful
Hard-limits = physical end stops in my case (the orange bits stop the bearing blocks from coming off the rails)