Centroid Community CNC Support Forum

I need to my spindle to travel outside the soft limits of my machine during tool change. I cant see a ways to do this. My old controller had an M code that disabled soft limits during tool change.

Normally I don't want the spindle to be able to travel out of the green area. During tool change it needs to travel into the blue area. Only the Y+ soft limit needs to be disabled or changed. If I was to just set the Y plus limit to include the green and blue areas, it is easy to crash into the red areas which is where the tool racks live when they are hidden away.

Any ideas?

You can modify the software travel limits through CNC system variables #23501-#23508 and #23601-#23608.

I would set it up so that the Y axis homes in the plus direction, to a home switch that is separate from the Y+ limit switch, so that Y home is where you have "+Y Limit" marked on your diagram.

In normal operation (outside of a tool change) you would then have a non-zero Y minus travel limit; and zero for the Y plus travel limit (prohibiting movement to the plus side of Y home).

You could then have your M6 macro set #23602 to a positive value when it needs to move Y into the tool-change zone; and set #23602 back to zero when it is done.

The only problem with this is that, if you interrupt the tool change before it finishes running, you will be left with the extended travel limit in place. You can partly work around that by also setting #23602 to zero in your cncm.hom macro, so that it at least gets reset on startup. If you wanted additional insurance, you could also set #23602 to zero in an M3 macro, so it gets run in nearly every program cycle.

Thanks for the explanation. I did look at those variables but thought they were read only. I just rechecked the manual and they are actually read/write so that solves that problem. I have to stop doing this stuff late at night!

If interrupted mid tool change, the old controller would run with no limits on any axis so this is not quite as bad!

I'm trying to modify my M6 macro to modify the y axis soft limit so that when I move the machine to the tool changer, make the change, and then once done, set the y soft limit so the tool can't contact the tool changer. For my config, the Y axis is axis 2, so I assume I would need to modify #23502 to make this work. I have the CNC PLC Macro and skinning manual but am not seeing a further description of travel_minus other than what is shown on pg139. I certainly could be missing something, but I can't find it. Does anyone have an example of reading and modifying the system travel_minus in a macro? Thanks in advance for your help!

I did exactly this in my M6 macro. I'm not near the machine right now to get it. If you search my name you should be able to find a report.zip file with it in there though.

The only catch was that if you cancel/stop during a tool change, then you get left with the y limit wrong. But running a successful tool change fixes it.

My M6 is for a rack type tool changer.

ashesman wrote: ↑Sat Apr 13, 2024 4:29 pm I did exactly this in my M6 macro. I'm not near the machine right now to get it. If you search my name you should be able to find a report.zip file with it in there though.

The only catch was that if you cancel/stop during a tool change, then you get left with the y limit wrong. But running a successful tool change fixes it.

My M6 is for a rack type tool changer.

Thanks for the info, I managed to get it working after looking at your M6 macro. I ended up making some changes to my homing and parking macros as they were effected by changing the limit as well. I now have one less method to crash the machine.