Workhorse Z-Probe

This machine is so annoying… Why do I need to manually tune the z-probe height every time after auto-leveling completes?! Is there a better way to do this?

It depends.

Why do you have to tune?

If the nozzle touching the washer at any corner results in ANY visible movement of the bed, your nozzle is not clean enough for probing and the tuning you’re doing is to compensate for the inaccurate reading from the dirty nozzle. Ensuring the nozzle is clean is a must, until you give up and install a BLTouch adapter and customized firmware to use that instead of the washer-based system.

If there is no visible movement, and you’re pushing in the wheel to do the live Z-height adjust during the first layer, then you just need to change your z-probe offset in the menu, and save your settings.

There’s also a chance you’re operating with some modified startup GCODE that manually set the Z probe offset, but that is unlikely unless you’re using a public printer (or you did it yourself and forgot you did that. That happened to a um, friend of mine.).

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@Wrathernaut I am having a similar issue with my workhorse though I haven’t manually adjusted anything. I was getting a bunch of prints done with it over the Christmas Holidays, but I noticed I had a large amount of filament collecting at the heat break so I went in and cleaned the entire tool head. Afterwards I have been having this issue where when it goes to probe the bed it drives into the washer and then pulls back and wipes the nozzle over and over again.

I’m getting the visible movement you mention which off course does not seem right. I did eventually go into the configuration settings to see if I should adjust the z-probe offset as I had just left it to the default from when I had updated the firmware, but I haven’t had any luck yet adjusting that. I read through the calibration guide OHAI, but how should I go about deciding what the offset should be if I can’t actually get it to print again? I do have the original offset recorded so I reset the z-offset to that, but it still is bending the bed when it tests.

After cleaning the nozzle again, I used a multimeter to test if there is continuity between the nozzle and the red ground wire on the heat sink and I am getting <1 ohm of resistance between the two. I am also probed the washers on the bed and get continuity between all of them. I decided to check the heat sink during the bed leveling sequence where it probes the front right washer and I also am getting continuity between the washers and the heat sink during leveling. I’ve tried both the bed level and auto calibration tests and the tool head will just drive into the washer or the calibration probe point (just to the left of the front right washer mentioned previously). To me it seems that I must have ruined the connection from the heat sink to the ground wire that goes to the controller so it just keeps driving down despite having continuity. Is there a way I can test the wiring or diagnose if it is getting the signal or not? It seems pretty clear to me that it’s not, but I’m not sure where the issue actually is.

Maybe my nozzle isn’t clean enough still, but I would be surprised if that is the case given I have continuity between all the conductive parts on the tool head and the bed during the leveling/calibration sequence. I saw @WhereNerdyIsCool’s video about his Taz 6 where the ground wire had been damaged and removed (timestamp=3:00 Lulzbot Taz 6 Repair and Upgrades - YouTube), but my wire is still attached. Maybe there is a short somewhere in the wire. Thanks for the help.

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Where is the filament buildup occurring?

It is possible that the nozzle is no longer secure and is now leaking.
If that is the case, what happens is the filament works into the threads of the nozzle/heater block/heat break and insulates the nozzle from the rest of the Tool Head.

When that occurs, the probing will fail due to lack of electrical connection.

@McLeach Thanks that would make sense, but I didn’t get this issue when the buildup was happening only after I cleaned up all the parts. The buildup was occurring on top of the heat block. I tore down the entire part and cleaned it out and then put it back together. Before with the buildup I wasn’t having any problems, but when I decided to clean it up and I reassembled the tool head that’s when I started to get the problem. I don’t believe at this point there is any filament insulating the nozzle from the rest of the heat sink and the ground wire as I can get an electrical connection between all of the different parts. With my multimeter I measure around 0.8 ohms between the nozzle and the ground wire connection to the heatsink.

With the filament building up above the heater block, that really tells me that the nozzle loosened up and that is what is causing the issue.

When reassembling, did you ensure that the zero sense wire was contacting a metal part? I have seen some users install it over plastic by mistake.

Further, when assembling, did you heat tighten the nozzle assembly?
That ensures there is good contact with everything and when it heats up, it does not further loosen and drop connection due the the expansion of the metal components.

@McLeach I did attempt to heat tighten the nozzle assembly though I’m no expert so I could have messed that up. I saw somewhere in the OHAI instruction for doing that before, but I couldn’t find it again when I did it this time. I used a heat gun and then the actual heater to do it.

Is the zero sense wire the red grounding wire that attaches to the heat sink?


This is the image from the OHAI since I’m at work right now, but this is the red “grounding” wire I’m talking about. Mine is attached to the top left fastener instead of the one pictured here.

That is the zero sense wire, yes.

I’ll have to check some stuff when I get home and see if I can correct the issue. Thanks for advice and the help so far.

I’m pretty sure @McLeach got it: improperly heat-tightened nozzle is now partially insulating it.

You’ll always get continuity, but remember that the difference between a good level and poor not is something like .05mm. Any delay from plastic in or on the nozzle that screws with the timing on that continuity check will greatly affect it.

It sounds like you need to get the nozzle off, clean out the heaterblock, and then do a proper heat tightening. Heatgun is more likely to damage your plastic parts than help. After getting every spec of plastic out, tighten the nozzle back in, and (without filament in the extruder, of course) heat it up to about 170c. Power the machine off, and tighten the nozzle while holding the heaterblock stable (away from wires, of course). Power up, heat to 190c, power down, tighten again. Repeat at 220, 250, and 280c. The amount you’ll be threading it in after the first heat tightening will be very little, but remember that you’re pushing filament out of a .6mm hole, so the hydraulic pressure inside the nozzle is quite surprising, and any gap in the threads is going to be filled.

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@Wrathernaut Thanks for the detailed heat tightening instructions. I’ll do another thorough cleanout and try again. Really appreciate the help and the great community here.

@Wrathernaut @McLeach Ok so I’ve gone through and cleaned out my hotend I had just a little bit of PLA in the nozzle but that was it. I’ve gone through the heat tightening sequence and ran both the auto calibration and the bed leveling sequences that are part of the most recent firmware for the workhorse, but I’m still getting the same issue where the printer does not sense contact when it touches either the calibration point or the first probe point washer.

During the leveling sequence when it attempts to make contact with the washer it moves relatively quickly and then presses down hard at that corner until it reaches a limit then it resets and wipes the nozzle to try again.

For the auto calibration sequence it just presses into the calibration point and I hit the power switch so it doesn’t press too hard.

I’ve checked the conductivity from the nozzle to the zero sense wire and I get a reading of 0 ohms from my multimeter. Am I missing something about how the printer is checking the z-height for both of these sequences? It seems pretty straightforward to me and that there must be another place to diagnose for issues besides the nozzle now. Is it possible there is a short or break somewhere in the zero sense wiring to the control box or in the wiring from the bed to the control box?

Since it was working before I don’t think this is very likely and I must have done something wrong with the assembly (the heat tightening being an example) and/or damaged something related to this probing sequence.

0 Ohms for most multimeters means no connection at all.

There could be a break in the circuit from the zero sense wire to the main board, you can check from the zero sense wire connection on the toolhead and bed, to the corresponding wire going into the mainboard.

For the bed, it’s ZMIN:

The Extruder’s zero sense wire should go through to the common ground:

It’s one of the black wires coming of the E1 harness wiring through the panel at the back:

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If you have a multimeter with continuity testing with an audible tone for continuity, that is what I generally recommend.

Here shows where/how to probe for continuity and how to work your way back to the board/ground post.


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