Solved Z Axis limit switch puzzler

Watch first video here:

http://community.robo3d.com/index.php?threads/helpful-videos-novice-expert.7478/

While it may seem complicated, it is not really

One of the switches is misfiring (showing open when you expect closed). It is likely either out of position so that instead of being closed (pressed against crossbar) it is down a smidgeon and open or the wire/connection is loose.

 

On the Z limits? No nothing to lubricate. The adjustment is as mentioned in the video: loosening the carriage mount that holds the switch and making sure it is snug up against the crossbar with the Z Nut fully seated in the crossbar (and all of that done with the extruder in the air/off the bed).

Other than that a bad switch or wire or other electronics is the only real culprit and that is less likely so make sure you can rule that out.

You can test the switches at any time/position by issuing an M119 in the Gcode terminal while connected to the printer. That will tell you what the printer "sees":

> M119
Reporting endstop status
x_min: open
y_min: open
z_min: TRIGGERED
z_probe: open
filament: open

 

OK, that is 10mm off the bed and probably should not be reading triggered


Endstops are reported as either “open” or “TRIGGERED”.

(where triggered is "home")

 

The Z rod length has no impact on this in any way since it is simply a mechanical check of the carriage being positioned correctly on the switches. If the Z Rods are physically there and the carriage is moving up/down then there is no issue with the rods.

I have had switches go bad, but usually they fail in one state or the other and not really get "intermittent" failures, but with a switch anything is possible so you can't rule that out.

It does begin to sound like one of the switches is the problem if you have ascertained that they are both mounted correctly on the Z nuts and that the Z nuts are also mounted/fitting correctly into the crossbar.

 

Maybe, if the X rods are putting enough pressure on the Z rods and you have the case cover on with the tops of the Z rods captured ... maybe.

You could test that by removing the case This will let the Z rods expand out the small amount and that might impact it.

I have (other than the C2) exactly one of three other R1/R1+ printers that still has a cover on it. I just don't leave them on.

 

Then I have a hard time imagining that the X rods are pushing it out far enough to do that.
I mean, that would be a lot more than a mm or two I imagine. The crossbar itself is the key part here and that didn't change.
More likely still a switch either out of place or defective. Make certain that the Z nuts are all the way into the crossbar and that the switches are freely moving and NOT loose in the mounts.

Could it be the wiring or the RAMPS? Yea, but that is much less common.

 

The while concept here is that the Arduino drives the Z down until one of those switches shows "triggered" (which means it is open) and then it knows the extruder nozzle is on the bed.

Yes, if they are bowing I would address that Let us know

 

Excellent catch