2nd Hand Taz Workhorse - multiple issues

[PWn3R]

Hi there,

I bought a Taz Workhorse 2nd hand, and I have some issues. I can’t seem to get the PLA+ to stick to the bed. I’ve tried temps ranging from 60-90c, and what’s coming out of the printer seems to stop sometimes or not start before it starts printing. I’ve tried nozzle temps from 205-245.

The bed is perfectly clean, I’ve scrubbed it with IPA. I do not have a fan shroud because it broke in the box on shipping and I’m trying to get it to the point that I can print a new one. I also noticed that the rectangular part around the nozzle is lose and rotates, which I can’t tell from pictures if that’s normal. I also had PLA coming out from ABOVE the rectangle above the nozzle earlier and no PLA coming out of the nozzle of the extruder. I’m guessing this is not supposed to happen.

I tried doing some looking around online, which is where I found the advice to clean the bed, which now looks flawless and brand new. I’m running out of ideas, and am wondering if this extruder head part is broken.

[TheVirtualTim]

A few things …

First… welcome to the forum.

As for the issues… I read the problem about the PLA+ not sticking and various bed temps … but all that got pushed aside as soon as you mentioned the broken fan shroud and loose heat-block. You’ll need to get those two issues sorted out before worrying about proper bed temps. (For the record, I print PLA using 230°C for the HE 0.5mm head … this is the head that comes with the printer and it is a “hardened” steel hot end capable of dealing with materials and temperatures beyond what many other printers can handle (hence the “Workhorse” name.). LulzBot sells many optional nozzles from 0.25mm for small parts with high detail; 0.5mm in brass vs. hardened steel nozzles; a 0.8mm nozzle with an E3D “volcano” hot-end for printing at higher speeds and good for larger parts, and a 1.2mm nozzle which also uses the E3D “volcano” hot-end for really big parts at really fast speeds. It’s pretty easy to swap the tool-head.

On to your issue…

The “rectangular part around the nozzle” is the heat-block. There are two cylindrical things inserted into this nozzle … the larger one is the heater cartridge; the smaller is the thermistor. The thermistor (variable resistor sensitive to thermal heat) tells the printer when the heat-block is at the required temperature and the heater cartridge is the thing that makes it hot.

It must not be allowed to be loose. This will result in a filament leak and that will cause other problems such as bed-leveling errors.

The extruder has a “cold” end and a “hot” end. The filament enters the “cold” end. There is a heat-sink and a cooling fan which is constantly blowing air through the heat sink when the printer is operating. This is to keep the “cold” end cold. It must not be allowed to heat up … the filament must not melt until it reaches the “hot” end or you’ll have issues with jams.

The “hot” end must be hot to melt the filament. To minimize heat flowing from the “hot” end to the “cold” end there is a gap to reduce thermal conductivity. The gap is called the “heat break”.

Here’s where the loose “rectangular thing” becomes important. The heat brake is a threaded tube. It threads into that “rectangular thing” (the heater block) from above. The extruder nozzle threads up from the bottom. The end of the “heat break” and “nozzle” meet in the middle of the heater block and they need to form a seal. If they do not then melted filament will ooze through the gap, through the treads, and result in filament oozing up through the top of the heater cartridge. This melted filament acts as an electrical insulator and will result in the bed-leveling (which relies on electric conductivity) failing to accurate level the bed.

The heat-block is soft aluminum … over-tightening can strip the threads (and this happened to my printer). But under-tightening can result in a leak. So you want this to be snug … but don’t over-torque it.

You’ll need a 7mm socket for a ratchet drive. You’ll need to heat the heat-block to around 280°C and then snug the nozzle while holding the heater-block square. (If i were to change out the nozzle then I cover the print-bed with a damp towel so that if the 280°C nozzle falls on the bed … it wont damage the PEI. Not that you are changing the nozzle … you just need to snug it in a bit.)

Be careful of the wires going into the heat-cartridge and thermistor on the side of the heat-block. You don’t want to damage those. As the Wicked Witch of the West says in Wizard of Oz … “These things must be done delicately.”

The wire going into the side of the heat-cartridge is solid-core wire. Braided core wire can bend easily. But solid-core wire will break. Be careful not to bend the solid-core wire.

If you’d rather not deal with any of this … LulzBot will rebuild the tool-head for you if you send it in. This isn’t covered by warranty so there would be a charge for it. But they’ll send the tool-head back to you in working order.

It’s a great printer and mine has been very reliable. But I did have an issue with a loose heat-block due to stripped threads … which is why I caution you to be careful as you fix this. It is literally the only issue my printer ever had.

[PWn3R]

Okay, I did get a couple test prints out today, it got worse as the day went by. I want to confirm I’m understanding. First, the gap I have is going to go away by slightly tightening the nozzle itself. Second, I saw that I cannot use metal tools to tighten them, is that true?

I don’t care if the print for the fan shroud is kinda crappy as long as it works. I got an hour and 40 minutes into a print this morning of the blower shroud and the corners started coming off then the whole shape came loose.

[TheVirtualTim]

You can use metal tools … just be careful for two things.

1. When the printer is powered on, you want to avoid damaging the wires on the side of the heat-block. They could be damaged by breaking them … or by shorting them.

2. Snug the nozzle so that it seals against the heat-break … but don’t crank it too tight or you’ll strip the soft aluminum threads in the heat-block.

[PWn3R]

I just want to make sure I’m being clear about this: the leakage was coming out above the heat-block, away from the nozzle, then starting to drip down the side of the heat-block. I am going to try this later today.

[TheVirtualTim]

Here’s a diagram I created:

The nozzle threads need to seal against the heat-break tube (I didn’t draw the “cold” end of the extruder). The left-most image shows this.

The middle image shows the gap between the heat-break tube and the nozzle. This would allow filament to leak through the gap, up the threads and ooze out in places where it should not. This can happen either because the nozzle wasn’t snug or if the threads were stripped (i.e. as a result of over-torquing).

The right-most image is also bad … this one would give you the illusion that you tightened the nozzle because the threads will bottom out on the heat-block. But since the heat-break tube isn’t thread into the heat-block far enough, you still get a gap.

I didn’t bother to draw the heat-cartridge or thermistor … or their respective wires coming out of the side of the heat block.

When you thread a nozzle in or out … you should eat up the hot-end – and fairly hot. Snug the nozzle … and it will contract and tighten up more when it cools down. This helps create a good seal so that it wont leak.

[PWn3R]

Thank you SOOOOOOO much. This confirms what I was thinking, and I wanted to be sure I was understanding what I am doing. I really appreciate you taking the time to walk me through this. I completed the recommended steps, and here’s what I found. The heat block is loose and can rotate itself. Should I tighten that as well, or do I need to tighten something else (heat brake tube?) to get it to stop being able to spin?

[TheVirtualTim]

If the nozzle is snugged in so that it is sealed against the heat-break it will hold the heat-block in place – it should be loose at that point.

You do want to make sure the nozzle bottoms out against the heat-break and not against the heat-block (as shown in the diagram to the right). That would create the illusion that the nozzle is “tight” but in reality you’d still have a gap and the heat block would be loose.

[PWn3R]

The nozzle resembles the picture on the left, and it is tight. To be clear the nozzle did get rotated at least half a turn more than it was before, and it is tight now, but I was very careful not to over tighten. I was concerned because the heat block itself can rotate. Is that expected?

[TheVirtualTim]

That is not expected. I might give LulzBot support a call and ask about that. On my printheads, the threaded heat-break tube is very snug into the cold end – a very tight fit. I’m not sure how E3D assembles these and it’s not part of the LulzBot documentation because the Titan Aerostruder comes pre-assembled. LulzBot has to print all the 3D-printed parts to make the head, but the hot-end, cold-end, and extruder nozzle all come pre-assembled.

If the heater block is still loose then I’d be wondering if the heat-break tube is loose from the cold-end side … or if the threads in the heat-block are stripped. It is soft aluminum and easy to strip – which is why you shouldn’t over-tighten or attempt to work when it is completely cold (pre-heat to around 280-285° before removing the nozzle).

BTW, you can re-print the blower-shroud (fan duct). The part for that is here:

https://devel.lulzbot.com/TAZ/redgum/production_parts/printed_parts/blower_shroud/

I think LulzBot prints these in ABS

Do not use the .gcode file in that folder – recreate your own. Inspecting the gcode reveals it is for a Mini 2.

[PWn3R]

Thanks for the advice. I’m going to pull the filament and try to carefully disassemble the print head to see if the cold end is where the problem is.

[TheVirtualTim]

This isn’t terribly difficult to do … just be gentle with the wires and remember that the heat-cartridge wire is a solid-core wire – rather stiff. If you bend it too much it is easy to break.

There is a visible gap between the heat-block and cold-end where you should see a few millimeters of the heat-break tube (this is it’s purpose … to minimize thermal conduction between the hot vs. cold sides of the extruder). With your blower shroud off you can probably see which side of the heat-break tube is turning. If the heat-break tube remains in place but the heater block turns, then the bottom is loose. If the heat-break tube rotates with the heat-block then it is snug in the heat-block but loose in the cold-end.

[PWn3R]

Thanks for all the feedback. This is what I am seeing after disassembly:

It looks like the heat brake tube is not inserted far enough and the filament is going out of the side up and around. Can you confirm if the tube is threaded or not? I tried wiggling a little with fingers, but can’t move it. Not sure if it’s smooth or if I need to grab by the part with no threads with say pliers and thread it in more (needs to come out first because there’s a ton of PLA in there right now).

[TheVirtualTim]

That looks correct. The assembly instructions for the extruder is here: https://e3d-online.zendesk.com/hc/en-us/articles/360016764817-Titan-Aero-Assembly-Guide-Edition-2-

Note this is just the assembly of the E3D Titan Aero extruder and not the entire LulzBot toolhead assembly. But you can refer to this to see the heat-break.

[PWn3R]

This is a side view of the extruder. I’m trying to understand how I was getting so much PLA coming out of the top (there was grey in there too, but mostly red, the color I have). I spent about an hour carefully scraping the heat block with a razer blade to get the huge chunks/gobs off.

At this point I’m thinking I need to heat the end up disassembled and try to check the that the heat brake and the nozzle are tight, or do you think I should remove the heat brake and inspect inside the heat block?

Edit: I just inspected the end of the heatsink plate that tightens down on the threads of the heat brake tube. There is grey PLA (or some kind of plastic) on that as well, and into the first two rows of threads.

Edit2: I think I see the problem here:

My nozzle may not actually be completely tight, I’m wondering if there is so much plastic in there lose that I need to disassemble completely and get it out to have a chance of getting these together tightly.

[TheVirtualTim]

You should have a slight gap between the nozzle and the heat-block when it the nozzle is tight. If you don’t have the gap, then it means the hex-nut fitting on the nozzle will “bottom out” on the heat-block before the threads “bottom out” on the heat-break. You have to make sure there is no gap between the nozzle threads and the heat-break threads – those two pieces press together inside the heat-block to form the seal to prevent filament leaks.

[PWn3R]

Yes, the few pictures I see on the Titan site seem to suggest that maybe my Nozzle is not all the way up. Is the best way to do this to heat it up to disassemble or should I take it apart cold to try to look inside and see if I have it totally gunked with plastic inside?

[TheVirtualTim]

Cold filament will act like Lock-Tite – making it difficult to extract anything from the heater block once the threads have filament on them. Heating it not only takes that problem away, it also expands the parts so that once they cool and contract you get a tighter fit.

To clean the inside, I use clear nylon filament. Heat it up, feed the filament in until you see it extruding through. Turn off the heat and let it cool down. Now you’re ready for a “cold pull”.

To perform a cold-pull … fully loosen the tension on the idler arm (turn the knob all the way clockwise to relieve spring tension).

Turn on the heat again … but this time be ready to manually “pull” the filament out. Somewhere around 140-150°C the filament will melt “just enough” to release from the tool-head. I use one hand to bull-back on the idler-arm and the other to pull up on the filament.

The Nylon will have formed around any debris stuck inside the head an pull everything up with it.

If you wait too long (over-heat it) then it will melt through and through and you wont get a clean extraction. You want to pull just at the moment when the outer bits of the filament (that would cause it to adhere to the hot-end) melt enough for it to pull free – but before the inner parts are melted.

You can “cleaning filament” which is just short (pencil length) bits of nylon. I ended mistakenly buying a whole spool of nylon (I swore I picked clear PETG and didn’t notice) – so since I have it anyway … I use it for cleaning.

You could technically do this with other filaments … but nylon is very strong (wont break when you pull up) and has a high temp. And if you get the clear stuff … you can visually see what it pulled out and be confident that you cleaned out the head.

[PWn3R]

This clearly is not assembled correctly. When I fully insert the heat brake into the heatsink for the cold end, this is the position it is in:

I think the heat brake is screwed too far into the heat block, and the nozzle is not inserted fully, and I also think that there is plastic in between the two inside the heat block, which is probably preventing me from screwing this together tightly. I did a 100c cold pull this morning before taking this apart, but it looks like it just ripped off inside the extruder head.

Do you think I need to try to reassemble this partially and heat it up disassembled so I can unscrew everything?

[TheVirtualTim]

To square-up the heater block, warm it up, loosen the nozzle, square the nozzle to the right orientation and hold it there while snugging the nozzle back in.

I think you mentioned you have a broken blower-shroud (so you’ll need to re-print that) – but here’s the right orientation so that it will fit within the shroud once you have that re-printed.

Note this is the SL 0.25mm head (my HE 0.5mm head is on the printer now but the lighting at that angle is poor – the SL 0.25, SE 0.5, and HE 0.5 heads all look the same. (The HS 0.8 and HS 1.2 are different – different fan shroud and they use an E3D Volcano heat-block which has a longer heating path to deal with the fact that filament moves through those nozzles much faster.)

In this orientation, the heat-cartridge and thermistor wires are on the BACK side of the heat-block (as seen from the front of hte printer).