Home switch clarification

I didn't want to hijack another thread I saw homing discussed.

There was talk of the axis coasting to a stop after the switch is toggled

. My plan was to use one of the cheap flat toggle type switch at the end of the travel for home and limit.

But I'm not sure if I want it to slam into the switch. There are basically hard stops with the way my motor brackets work currently I've been shutting down at my home as I haven't had any projects to continue yet.

You can set up soft limits. Set HOME, MIN_LIMIT and MAX_LIMIT so after homing using the switch, linuxcnc knows where the end limits are and will not run into the switch.

Leon82 wrote:

There was talk of the axis coasting to a stop after the switch is toggled

That was me!!!

I found on my plasma table that on homing the axis coasted past the home switch and needed to remain triggered yet if it hit a limit switch, the machine stopped dead in its track!

So after some experimentation, Here is how I configured my home and limit switches on the travelling part of the axis.

The left prox sensor is the limit, the middle (lower) prox sensor is the home switch and the sensor on the right is the limit switch for the other end of the axis.

So on homing the axis moves to the left until the home switch is triggered by the right edge of the sensor plate. It then coasts to a stop along the flat section of the sensor plate. Then LCNC move the axis off the home switch and approaches much more slowly to accurately locate the right edge of the plate.
Finally, I have set a homing offset that then moves the axis as close to the limit switch trigger (the 10mm square higher section) as I could get it to maximise axis travel.


You can reduce the distance it coasts by slowing the homing velocity down and if you have a heavier axis like a milling machine, it might not coast much at all!

Hakan wrote:

You can set up soft limits. Set HOME, MIN_LIMIT and MAX_LIMIT so after homing using the switch, linuxcnc knows where the end limits are and will not run into the switch.

This comment is not really addressing the issue. But yes, you need to set your soft limits so you stay inside the limit switches (eg per the first photo where the axis is right on the soft limit).

Anyway, I thought this was pretty cool original design and it works a treat.Feel free to copy it.

Ok thanks

They are setup as software limit. I'm going to do the zero on the + side as home /limit

It won't let me move the axis after it homes. It shuts off the machine because it's on limit.

I set is as just home and is works

Maybe I ha e to put in a z home offset for it to work as a home+limit.

andypugh wrote:

You need to set a HPME_POSITION that is off the switch, then the final part of the homing sequence is a move off the switch before re-enabling the limit switches.

And thats why I like seperate home and limit switches as shared ones eat into your axis travel

Tjanks, I'll give e it a shot