Taz Workhorse Bed Leveling issue

Hi all,

I’m having an intermittent issue with the bed leveling on my Workhorse.

When auto-leveling, the nozzle will push the washer down a few mm, torquing the bed. I used the included brush to clean the nozzle thoroughly before leveling. It’s not failing to make electrical contact, because leveling does succeed. It doesn’t do this to all washers - the few times I tried this, the back washers touched off fine, the front right washer was intermittent, and the front left washer reliably gets pushed down.

My machine has all the feet on a table that at least seems to be level, although I will try again on the floor and see if that changes anything. Is there anything else I can try?

If you have a multi-meter, check the ohms between the nozzle (make sure the nozzle is clean) and heat-sink. The “cold” end of the extruder has four screws around the aluminum heat sink. one of the screws has a red wire attached. That is the “zero sense” wire used to conduct back to the board to detect when the nozzle touched a bed washer.

If you measure the ohms between the nozzle and the red wire, you should read less than 1Ω (my printer typically reads around 0.7 to 0.8). If it’s reading high … then something is acting as an insulator.

What can do this?

The extruder has a “hot” end (the heater block), a “cold” end (the heat sink where you see the fan attached), and a “heat break” that separates the hot and cold ends with a threaded tube running between the two halves.

The “heat break” threads into hot-end from above… the nozzle threads on to hot-end from below. But the two threaded parts should come together in the middle of the heat break and they create a seal.

IF they aren’t sealed, filament can leak through the gap … make it’s way through the threads (remember it’s in a melted state and under a bit of pressure) and this reduces the conductivity because they aren’t solidly touching … with melted filament acting as an insulator.

You would be able to tell by inspecting the “heat brake” (the gap between hot-end and cold-end of the extruder). If you look in that gap … you should just see the threaded tube … no plastic. If you see melted filament in there… that means it has been leaking and it needs to be cleaned.

This did eventually happen to me and I had to clean mine. The process is moderately tricky… you can’t just grab a wrench and take it apart.

It’s difficult to inspect the heat-brake with the part-cooling fan duct attached. The bottom two screws on the aluminum heat-sink are also holding the fan-duct in place. Remove those two screws … BUT … the fan will come with the fan-duct and the fan is plugged in. You don’t have to disconnect the wires … you can let it dangle, just be gentle so as to not rip out any wires. Also … the screws are not the same length so remember which screw was in which corner.

With the fan duct removed, you can inspect the heat-brake and make sure it you don’t see any melted filament in that gap. If you do… this is likely why you are having un-reliable bed leveling.

I’ll leave the cleaning instructions for a different post here because if your printer is still under warranty, you might want to call support rather than attempt to clean it on your own. I did clean mine on my own (and it’s under warranty) but I was comfortable with the process and had all the tools needed.

The process is a little tricky because the extruder nozzle and heat-brake can only be disassembled with the extruder “hot” at 280°C … attempting to unscrew it while cold often results in the threaded heat-break tube shearing and then you have to replace it. There’s a bunch of steps required and some steps require heating up the extruder. This was enough work that I think the average owner should think twice before deciding to try this on their own. This is why I suggest that if your printer is under warranty… call Support.

If you are no longer under warranty and you want to undertake this yourself, let me know and I’ll provide the steps I used to clean mine. It is a bit tricky to do and you also need a decent soldering iron (with the heated tip scrubbed clean).

Thanks for the super detailed instructions. I’m sure this will come in handy in the future if I ever need to disassemble my extruder.

For the time being, I scrubbed the nozzle very well and checked that conductivity was good between the nozzle and other (presumably grounded) parts.

I also replaced the wiper pad. I’m not the expert here, and I haven’t looked to see if there are other opinions floating around about this, but it seems like the wiper pads on this model are less effective. The very first print, the extruder plunged into the pad and left a rather deep channel, which I believe rendered subsequent wipings ineffective. The wiper pads I got are rather less dense than the ones on my Mini, and in the sideways orientation seem prone to delaminate when you drag an extruder tip through them. After a few wipings it seems more likely to pick something up from the wiper pad rather than deposit anything.

I replaced the wiper pad and the Workhorse has leveled properly several times in a row. I’m going to replace the pad with one of the extra pads from the Mini as I believe the density of that pad will do a more consistent job.

We had numerous issues with bed leveling and such.

One thing you can try is removing all the filament from the extruder head. Make sure to heat it up good so anything in the nozzle that could drip out comes out too. Then clean the nozzle real good with scotchbrite pad. Clean nozzle while it’s hot. Be careful.

Then, with no filament in the extruder at all, run the bed leveling program.

It’s a sure fire guarantee you have no cold filament stuck on nozzle getting in the way.

I also found out on one of the threads here that if your bed is out of level by more than something like a 1/2 mm the auto-bed level won’t work. There’s a program that runs around and checks the four corner’s height. You may need to shim a corner or three to get the bed level close. That’s what we had to do.

Also, there’s that metal calibration cube on the front of your bed too right?

With the cleanest nozzle you can get, and no filament in the nozzle, run that calibration.
One time we did it and damn if the nozzle didn’t almost punch through the glass build plate.
I hit that big OFF switch real fast.

I had to google search all kinds of things to get some fixes for the Workhorse we got.

Bottom line - don’t assume the auto bed level feature works perfectly. You may need to physically shim a corner or three to get bed close to level before that’ll work.

Read this thread: https://forum.lulzbot.com/t/solved-taz-6-auto-leveling-is-0-5mm-off-now-perfect-to-0-01mm/6250/5