Quick question about Z endstops and z-probe



  • I have an Ender 3 that I've had working with the Duet 2 WiFi board for some time now, most recently on v3 of the firmware, and things are working well. I've been using the BLTouch for Z-homing and mesh bed leveling and I quite like it, but the Ender also has a two-wire switch on z which at present is not configured.

    Is there any benefit to using the z-switch for homing z, which X & Y already do, and just using the BLTouch for mesh bed leveling? If so, how do I go about configuring that.

    My configs are here


  • administrators

    Assuming your BLTouch is reliable, there is no benefit to using a separate Zmin endstop switch.

    Some users like to have a Zmax endstop switch so that they can home to Z max when resuming a print after a power failure.



  • @jrsphoto As @dc42 said, there is no benefit in using the switch for homing if your BL touch is reliable. But if the switch is already in place and you want to make use of it, you could use it as a backup in case the BL touch every failed. To do that, you set the switch so that it will trigger a short distance after the BL touch would normally trigger. You wire it to a spare end stop then use M581 to initiate an emergency stop if it ever triggers. https://duet3d.dozuki.com/Wiki/Gcode#Section_M581_Configure_external_trigger


  • Moderator

    Here's a guide that shows moving the Zmin endstop to the top of the frame for use a Zmax endstop.

    https://duet3d.dozuki.com/Guide/Ender+3+Pro+and+Duet+Maestro+Guide+Part+5:+Upgrades/54#s212

    Useful if you like to move the gantry entirely out of the way at the end of a print, or if you need to rehome the printer after a powerloss before resuming.



  • Thanks guys;
    So what about a dual independent z-motor configuration? I'm not currently using two z motors but given recent purchased by me, this is something I may need to do. Honestly, only thing really stopping me was that I didn't understand how best configure the two Z end-stop switches so that the X-axis would home level,AND have the BLTouch for mesh bed leveling as well. Or maybe I don't need mesh bed leveling with dual Z endstops, but it seems like the would still be some benefit.


  • Moderator

    I wouldn't bother with adding a second lead screw to the ender 3. The bed has leveling screws to adjust for tilt. It's also a very small bed, so it's not that hard to get it leveled. Furthermore, tilt in X is only one issue. There is also tilt in Y and more importantly the shape of the bed surface which a single axis tilt can't correct for. Mesh compensation however can correct for all of it.



  • The problem is, my Ender really isn't an Ender any longer. The weight being supported by the single leadscrew, and driven by a single motor is significant. And I've got an E3D Hemera that needs to go on.

    after.jpg


  • Moderator

    Well if you think there is significant deflection perhaps a second lead screw would be beneficial.

    Setting up the independent z motor leveling isn't too difficult. You don't need dual endstops to do it if you have a probe already. It probes one side and then the other and adjust the motor to level it to the bed. You can also use mesh compensation on top of that to map out the bed surface and any other existing tilts or deformations.

    https://duet3d.dozuki.com/Wiki/Bed_levelling_using_multiple_independent_Z_motors



  • @Phaedrux said in Quick question about Z endstops and z-probe:

    Setting up the independent z motor leveling isn't too difficult. You don't need dual endstops to do it if you have a probe already. It probes one side and then the other and adjust the motor to level it to the bed. You can also use mesh compensation on top of that to map out the bed surface and any other existing tilts or deformations.

    Yeah, that's where I'm at. I need to figure out how to config this. Either with dual z endstops or using the bltouch for both.


  • Moderator

    @jrsphoto said in Quick question about Z endstops and z-probe:

    Either with dual z endstops or using the bltouch for both.

    Well Z endstops aren't even necessary technically. For example, prusa printers just drop the motor current and drive the Z axis up until each motor stalls out, which squares the x gantry to the frame. It would be trivial to do something similar if that's all you needed.

    Otherwise, using the probe as described in that link is the prefered method since it's using the actual bed surface to find the position and tilt of the bed. If you use endstops, you're leveling the gantry to the endstops, not actually the bed. Since you have the probe, might as well use it.



  • @Phaedrux said in Quick question about Z endstops and z-probe:

    Otherwise, using the probe as described in that link is the prefered method since it's using the actual bed surface to find the position and tilt of the bed. If you use endstops, you're leveling the gantry to the endstops, not actually the bed. Since you have the probe, might as well use it.

    My concern with not using endstops and leveling the gantry to them, is I'm using linear rails and they need to be kept inline from my understanding. I could be wrong.


  • Moderator

    Well that's another thing. If you think you're getting noticeable deflection, that would mean there is enough play that correcting the deflection should be ok, but yes, there should be enough compliance built into the x gantry to prevent binding.

    I would have thought that with the dual rails like that you wouldn't have had noticeable deflection to begin with.


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