Nozzle missing wiping pad

General LulzBot TAZ
1

I’ve been having a lot of issues with my TAZ workhorse since it arrived and haven’t been able to get a successful print. The printer now fails the auto-leveling process at the beginning. I thought the nozzle could just be caked with filament and manually told the printer to wipe the nozzle using the CURA software.

What I noticed was that the nozzle doesn’t go into the wiping material on the side of the build plate. The nozzle seems to be misaligned on the x-axis by a centimeter or two. The print-head goes through the wiping motion but the nozzle is entirely over the build plate.

Is there a way for me to re-calibrate this?

2

There are two issues to check. (1) is the printer able to ‘home’ each axis correctly, and (2) is the bed-leveling system getting adequate electrical continuity for the leveling process.

Each of these are actually pretty simple things (the printer is, in some ways, simpler than you might suspect… very simple electrical continuity is used to determine when an axis has hit it’s travel limit and a similar system is used to level the bed. Either it conducts or it doesn’t. It can be as simple as a wire that came loose.

Homing

This is all based on ‘homing’ the printer (the G28 command) … which runs each axis until they hit their end-stops.

You can test the printer by going into the “Console” (you’ll find a button to open the console on the “Monitor” panel of Cura). This is an interactive terminal window that lets you type direct commands to the printer.

In the terminal do a ‘G28’ command (home all axes). Watch for any error messages.
Then test out a few moves such as: G0 X100 F2400
That will move the X axis to 100mm in from the left of the build plate and it will travel at 2400mm per minute (40mm/sec).
Then test: G0 X0 F2400 (this should move the X axis back to the left edge of the build plate)
Test: G0 Y100 F2400 … and also test G0 Y0 F2400
Basically you are testing to see if the printer will obey your move commands. If may refuse a move on an axis if it thinks the axis hasn’t been ‘homed’.

Leveling

The Workhorse should home itself, heat the nozzle to the ‘soften’ temperature for the particular filament (this varies based on the filament profile), it will back out a little filament, then cool to the ‘wipe’ temp (usually 170°C but this is also in the filament profile), then perform the wipe operation on the pad, then cool to the probe temp (usually 160°C) then probe each bed corner starting with the front left washer.

If it fails it means it didn’t get electrical continuity when the nozzle touched the washer. This could be many reasons.

The main reason is a dirty nozzle – make sure it is clean. You can heat it up and use one of the red scrubbing pads to clean it. I usually use the tweezers to pull anything clean then give it a scrub (these days I converted from the hardened steel nozzle, to an E3D Nozzle-X. Nozzle-X is also hardened steel but it has a coating that makes it difficult for any filament to stick to it. If anything does manage to stick, it wipes off easily because of the coating.)

There can be other reasons for a failure such as a disconnected or broken wire.

Grab your multi-meter and test out the ohms on each washer as well as on the head. Nothing should read more than 1Ω.

For example, I’ll put a probe on the calibration cube while putting the other probe on each of the four bed leveling washers. Make sure nothing reads above 1Ω.

Also put a probe on the red ‘zero-sense’ wire on the AeroStruder. This is the red-wire attached to the lower-right corner of the aluminum heat-sink. Put the other probe on the tip of the nozzle and make sure that reads less than 1Ω.

My printhead had a filament leak through the heat-brake. I wish I had a diagram to show but … your heat-block on the print head has a hole drilled and tapped completely through the block from top to bottom. The heat-brake tube threads down into that hole from above. The extruder nozzle threads up into the hole from the bottom. The bottom of the heat-break and the top of the nozzle MUST form a tight seal … no gap. If they aren’t tight, filament leaks through the gap, into the threads and eventually starts oozing out of the top of the heater block. If you inspect the heat-brake gap (the gap between the hot-end and the cold-end of the extruder) it should be clean. If you see filament in that gap, you’ve got a leak and it needs to be disassembled, clean, and re-assembled to have a tight fit.

Anyway… in my case, the “leak” means that the filament acts as an insulator … it works its way into the threads and instead of metal on metal, you have metal with polymer between it … so it barely gets any electrical contact. This will result in poor probing when it tries to level the bed.

It can be difficult to see into that gap with the fan-duct installed. The cold-end of the extruder is held in place with four screws (one in each corner around the heat-sink). These are long screws. The bottom two screws also hold the fan duct in place. If you remove them then you can pull down the fan-duct (careful not to strain the fan wire because the fan is attached to the duct) and easily see into the gap. BTW, these two screws are not the same length, so remember which one was on the left vs. right (although it’ll probably be obvious when you go to put it together and one is too short and the other is too longer… just swap them).

3

Is there a way to recalibrate the X and Y offsets? The X direction seems to be off by at least a centimeter.

4

The position is auto-calibrated based on hitting the X-axis limit switch. Here’s are a couple of photos:

IMG_1439
IMG_14393024×4032 2.08 MB
IMG_1440
IMG_14403024×4032 1.7 MB

In the second image you can see the switch located just below the X-axis motor. This a common bump switch. This switch can be wired to either ‘normally open’ or ‘normally closed’. The Workhorse uses the ‘normally closed’ wiring meaning that it is constantly allowing electrical flow … until the X-axis carriage bumps up against the button. That ‘breaks’ the contact and makes the printer realize it has homed.

The first image shows the X-axis carriage at the home position. Note that ‘home’ is actually X-50, not X0. X0 is the position where the head would be over the left edge of the build plate. But the printer has to be allowed to travel left of the build plate to reach the wiper pad … which is why the ‘home’ position is really at the -50mm position.

If that wire is disconnected then the printer will “think” it has homed the X-axis … no matter where it actually is (you would watch the print head when you ask it to ‘home’ and note that it never actually travels over and hits the limit switch button).

On my Workhorse, there was a break in the wire, I had to use a multi-meter to find it. Strangely it was in mid-wire (I expected maybe a bad crimp-job on one of the ends, but those were fine). The point where the wire had an internal break did not appear stressed, pinched, etc. it looked fine. It just didn’t conduct.

To find the break, I used a multimeter to test both wires going to the switch. One conducted as expected. The other did not. I inspected the wire that wouldn’t conduct for signs of damage or maybe a poor crimp-job on one of the ends… but they were all fine.

Finally, I clipped one of the multi-meter probes to the end of the wire, and the other end to a straight-pin (the type you’d use for sewing) and pricked the pin through the insulation on the wire so it would touch the metal wire inside. Sure enough… I eventually found a point along the wire where it stopped conducting. As I mentioned above, the wire didn’t show any obvious signs of damage or stress and it was an internal break. It had to be repaired.

In the photos I posted, you’ll notice that there are some bright yellow/green zip ties that hold the wires in place. On your printers those zip ties are black … I had to disconnect the zip ties to test and repair the wires and didn’t have black zip-ties on hand in a small enough size … the bright yellow/green was all I had, but it’s almost a perfect match for ‘LulzBot Green’ so I went with it.

If you do have a continuity problem, then things to have on hand before you tear it apart are (1) small zip-ties, and (2) heat-shrink tubing and a heat-gun if you want to re-wrap the fabric wire sheath (I suppose you could use black electrical tape).

If your printer is under warranty, call LulzBot. If you can verify the cable is broken, they may be able to send you a replacement. They did send a replacement to me (I think I paid the postage) but you’ll still need small zip ties.

5

Just in case someone else has the same problem. It looks like the bed shifted during shipment. The screws holding down the four bed mounts weren’t tightened down all the way and it became misaligned.

To resolve, I measured the distance the nozzle was offset from the wiping area and made some marks next to each bed mount with some painters tape and a pen. Then I adjusted each mount and tightened down the screws.

I’m not able to print and no longer have bed leveling issues.

6

I think this is good? Your last sentence said 'I’m not able to print" … was that a typo? Are you able to print now?

If need be, I can certainly the distance from say… the corner of the frame over to where the bed attachment points should be located. It may also be documented (and probably is) on the OHAI.LulzBot.com website in the assembly instructions.

7

thanks for posting this thread.