Z probe repeatability; hardware recommendations?



  • Ah! A fellow Wes! I've recently added one of dc42's IR sensors to my test bed machine. Hopefully I should be able to give you some independent repeatability information later today.


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    The IR sensor works well on opaque surfaces as long as they don't have huge contrast differences in different places. I no longer recommend it for transparent surfaces such as clear glass or PEI, because coatings (e.g. hair spray on glass) and scratches on the top surface change the relative intensities of the reflections from the top and bottom surfaces, which affects the trigger height.



  • I've had great success with the Piezo sensor. Uses the nozzle as the probe so very easy to setup.



  • Is the piezo available for printers other than delta?



  • Just entering the Duet world myself, I have a CR-10S I'm switching over. I'm not sure if the Pro has the same problem as a lot of the 10S machines do - the right axis will lose sync with the left when the motors are switched off (disable steppers or power down).

    This causes the left and right Z steppers to be at different heights after having been carefully aligned, and the bed leveled. Most people just measure it, move the right stepper by hand and relevel the bed.

    After many hours of mechanical adjustments I've minimized my problem to just a slight one, but decided to go with independant Z so the small remaining error will be picked up and corrected during homing. If you setup your Duet with the double Z connector like on the CR-10 controller, your Z axis motors are slaved to each other.

    I wonder if this may be what you're wrestling with, at least in part, since you find yourself tweaking with z-probe offset or baby stepping before each print.

    Try this to check for it -

    1. Home and level your bed mechanically (steppers ON!), then do a normal software Home using the Duet interface.
    2. Use a ruler and measure carefully from the top of the frame to the top of the X Rail, right at the right frame vertical member, then again at the left vertical frame. They should match. (Measuring X rail to top frame both sides)
    3. Then run the Z up 150mm and re-home from the interface. Now disable the steppers and remeasure the X Axis. You may find they don't match now, there's the problem! Many find the rail sags on the right. a very small few find the opposite.

    By going to independant Z (you have to add an endstop switch to the right side, I got a spare from Creality when I bought mine), you allow it to home the sides independently and fix any tilt.

    Again, I'm still setting mine up, and there's some really experienced people here who have it working, but your problem sounded familiar and is pretty subtle, might check if that's the issue.



  • @doctrucker said in Z probe repeatability; hardware recommendations?:

    Is the piezo available for printers other than delta?

    Yes however, it's not just plug and play unless you use their Orion module. Google Precision Piezo and they have a few options that may work for you. I use their Orion module on a self built Cartesian style machine but Thingiverse may have a setup that works well for your specific printer.



  • Thanks for the key words to search on. I have doubts on ot being suitable for my application as it's a cantilever x-axis. Hope to be wrong.



  • I have the Precision Piezo Orion installed on my big CoreXY printer and it works very well. It's reliable, repeatable and most importantly, uses the nozzle itself as the probe.

    You simply can't do better than having zero offset from nozzle to probe and it doesn't care what my print surface is.

    The Orion costs me no more than 10mm of Z-height and that's a drop in the ocean on everything but a mini printer.

    It is probably better suited to an Ultimaker style printer where the bed moves up and down rather than the hot end. If your printer's mechanics are smooth enough though, there's no reason why it wouldn't work on a moving hot end.



  • @grizewald Thanks; I've had my eye on the precision piezo, and I wanted to hear from people that have had good experiences 🙂

    https://www.thingiverse.com/thing:3001060 is a mount design for the Chimera+ that I'm hoping will work out.



  • @puterpro yeah, the left and right sides do tend to get out of alignment with each other. There are mods that use a timing belt to sync the two Z-axes (here's one: https://www.thingiverse.com/thing:2693296 but there are also more simple versions of it).

    I hadn't thought of driving them separately. I'm not sure I have enough stepper drivers for that once I've mounted the Chimera+ and hooked up both extruders. Regarding the extra endstop switch: the Pro doesn't have Z endstops, only a probe, so I think that I'd need to source and find a way to mount a switch on both sides if I were to pursue that.

    What do you think about the timing belt solution?



  • @wez - I thought so, very annoying. I played with mine a lot (the LEFT side wheels ate a big key to it) and got it down to just a little but ... That belt thing - It's one I seriously looked at about a year ago, I think it's a clever and elegant solution if a bit odd ... LOL!

    The switch mounts shouldn't be hard, the frame's the same and the Z endstop switches mount on the frame. Here's the simple one I added to my right side, it's adjustable. I just did a "Mirror" in my slicer and printed, works well.

    http://www.thingiverse.com/thing:2780362

    My original Z switch is on a more advanced adjustable mount (works very well):

    https://www.thingiverse.com/thing:2531282

    The only real concern I have with your setup is the motors are in series, not parallel like the original Creality setup. That offers less torque. But if you're running a Chimera you need the extra driver for the second hotend so ... Belt looks like a good way to go, just use quality bearings, not a thing to go cheap on!

    Good luck, and let us know how it goes!



  • @wez said in Z probe repeatability; hardware recommendations?:

    the Pro doesn't have Z endstops, only a probe

    You don't need to use two end stop switches to do leveling if you have a probe you can just use that. But if you're going to be using both extruder drivers you'll be short a driver for the second Z.

    Another option for leveling could be to use a physical hard stop at Z max and switch to stall detection with low motor current and basically run the z axis up to the top of the frame until the motors stall.



  • I'd thought about using Z-end stops on my CoreXY, but in the end, I rejected the idea and just use the Orion probe. The first thing my homing routine does is probe the centre of the bed to get the initial home point, then probe next to each Z-lead screw and use the independent Z-motors to cancel any misalignment which may have developed while the machine was powered down. This is then followed by a second probe at the centre of the bed to account for any change introduced by levelling the bed via the motors.

    This works very well and is simpler than trying to ensure that two Z-end stops are perfectly positioned to result in a level bed.



  • @grizewald Probing routine: That makes a lot of sense for my setup, I think I'll use that pattern, Thx!


 

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