Machine limit switch zero and user defined zero for parts?

Not seen those before. I'm betting there are microswitches indside that the two plungers activate.

Option 1 - take the things apart and see what's inside. Post a photo and we'll see what might be fitted as a replacement with better repeatability.
Option 2 - remove them and retrofit different switches.

The trick is to figure out what signals the switches send to the control so you can duplicate it with new switches. It may be a little fussy retrofitting NPN or PNP proximity sensors in place of the (probable) microswitches, but it's do-able.
 
I think it's just a regular old switch inside that thing with a 5v reference to ground.
 
Gotcha. Normally open or closed? What does the actual switching element look like?
 
I will have to check and get back to you. I will be in my shop tomorrow morning working on finishing up a part. I will try to open it up while I am over there. I'll do a continuity test to see if it's open or closed.
 
NC vs NO isn't really important, but it'd help. It may be more of a mechanical issue with the plungers than the internal switching devices - a bit of wear on the plungers or bores and they'll cock and hang up. Maybe.
 
Yup, just micro switches inside that housing. Be sure to replace them with slow acting switches, not snap action. Slow acting switches are much more repeatable than snap action.
 
The switch looks like the ones that Grizzly uses on their mills to limit power feed. Not really all that precise. They work OK as a safety mechanism to prevent hard crashes but IMO, are not repeatable enough as homing sensors for setting the machine reference on a CNC.

It isn't necessary to have an repeatable machine reference. You just have to reset your work reference each time you start your machine. The reason that I installed the precision homing on my CNC was so that I could shut my machine down for the night and start up the next day without having to redo my work reference.
 
I can't remember the last time I Homed the machine. I have been perfectly happy with just zeroing to the part I am making. I think, accurate homing only provides two benefits. `1. If you have a long complex sequence and need to stop part way and pick back up the next day or later. 2. if you are in a production environment where you can start work each day with the machine in a known state. Neither is of any real value to me. so I just zero for the part/cuts I am making at the moment.
 
Another problem with any kind of limit switch is the stopping point is based on the rate of travel which effects the stopping point once triggered. I have seen proximity sensors used as homing/stops in CNC machines, if the travel is set to a fixed rate approaching the sensor, then the repeatability is typically better than 0.001". Another issue with any switch is that you do not exceed the travel, so on my last mill I used mechanical roller switches and a ramp to limit travel. On the proximity switches I either have them perpendicular to the trigger service, or if inline they have a long sense range of 8-12mm. There are also some high quality sealed mechanical roller switches, I use an AB plunger type as a limit travel on my bandsaw which runs flood coolant.
 
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