Print Plate Temperature is Never Truly Uniform  

RE: Print Plate Temperature is Never Truly Uniform

Posted by: @tim-m30

Lay a small piece of filament on your extruder motor: let me know if it melts.

Did exactly that back then. It didn't. There's a post of mine here somewhere showing some very low temp hot pink rigid.ink laid across the extruder motor in fact.

Put that same filament inside a confined space with an uneven feed path and subject it to the friction of multiple retractions, variable extruder tension, variable heatsink airflow, thin layers with little filament movement, then toss in a bit of extra heat and I'm not about to say it can't happen. PLA spending time in the extruder is certainly going to be subject to more heat than at the surface of the motor. The symptom is filament snapped off above the PTFE, often with a blob that can't be pulled up and out of the extruder. Something caused that blob to form that high.

Chris W. is a pretty smart and thorough guy and I'm not going to dismiss his findings without doing some testing. The R3 part redesign wasn't done to deal with the stepped heartbreak. I just don't have a thermal cam to test myself. This is another me of those things that hasn't happened to me, but has been widely reported. The symptom is filament snapped off above the PTFE, often with a blob that can't be pulled up and out of the extruder.

RE: Print Plate Temperature is Never Truly Uniform

I'm in the camp that it takes an enclosure and minimum 75c static temps before PLA gets soft enough to deform to the degree seen in some of those photos.  And that sort of operating conditions is well beyond anything Prusa designed for; or any sane manufacturer for that matter. 

As for filament snapped off before the PTFE: my pet theory is these isolated cases are simple "Oops, I forgot to check my spool before the print and I ran out of filament with the filament sensor turned off."

RE: Print Plate Temperature is Never Truly Uniform

I'm still wondering how the Mosquito is supposed to be better in an enclosed chamber with higher ambient temperatures, maybe it maintains the slightly increased temperature in the cooling section at a more consistent level than the  E3d (Basically E3d more susceptible to environmental influences).

I can't fault the easy nozzle change, but maybe the improvement here is actually a longer heat zone, kinda makes sense for faster printing, bring the heat up before the melt zone, but not enough to bring it into softening territory, but keep it under control, then hit the heat zone and melt quickly for extrusion. The Delta T would be less so it would require less power, or be able to run at faster speeds.

RE: Print Plate Temperature is Never Truly Uniform

Posted by: @tim-m30

I'm in the camp that it takes an enclosure and minimum 75c static temps before PLA gets soft enough to deform to the degree seen in some of those photos.  And that sort of operating conditions is well beyond anything Prusa designed for; or any sane manufacturer for that matter. 

I'm sure Chris W. & the other people working on the issue will give your declaration all the consideration it merits. 🙂 Some simple searching has identified enough reports of the problem for me not to dismiss their work.

As for filament snapped off before the PTFE: my pet theory is these isolated cases are simple "Oops, I forgot to check my spool before the print and I ran out of filament with the filament sensor turned off."

To be clear: The symptom for this problem is not cleanly snapped filament. It's a molten blob that forms between the Bondtech gear and PTFE tubing -- often so large as to require manual removal -- with the filament still attached to the spool above. This is not something reported by only a handful of people. Unfortunately, the forum transition lost many of the images showing the problem. A lot of users reported very high extruder motor temps, those contribute to heat, heat contributes to problems.  Many people were able to mitigate the problem in a variety of ways:

• Cooling off the extruder motor with passive or active cooling.
• Outright replacement of the extruder motor.
• Adjusting or replacing the collet clip holding the PTFE tubing in the hotend assembly to reduce movement.
• Adjusting extruder tension screws.
• Adjusting idler axle.
• Adding thermal paste between the heatbreak and heat sink.
• Printing new extruder parts with better filament feed alignment.

The fact that one fix works doesn't mean others won't. We see problems that are the result of myriad variables, all of which must be within tolerance for a successful print. Problems anywhere in the feed path can contribute to problems. Not all problems have one origin. This is why I'd love to see some testing done with a FLIR setup. I try to keep track of all the problem reports and resolutions to correlate results. 

Edit: My parts are due today, so hopefully I can get back in the printing game.

RE: Print Plate Temperature is Never Truly Uniform

The molten blob isn't the same as the filament simply snapped off below the gears.   Clearly two different cases; and I do not dismiss them in any way shape or form. 

First is the melted blob - where filament is melted and piled below the Bondtech.  That case requires gear temperatures above 75c, and I do not argue this case is real and repeatable.  The extruder motor runs 35c above ambient. Raise ambient to 40c and you'll melt PLA with the Bondtech.  No rocket science required.

The second case, lone filament broken below the Bondtech, there are many reports of this, can be explained by simple filament runout.  I am generally inclined to go with the simplest explanation until proven otherwise.

RE: Print Plate Temperature is Never Truly Uniform

Posted by: @tim-m30

[...] First is the melted blob - where filament is melted and piled below the Bondtech.  That case requires gear temperatures above 75c, and I do not argue this case is real and repeatable.  The extruder motor runs 35c above ambient. Raise ambient to 40c and you'll melt PLA with the Bondtech.  No rocket science required.

Erm... I was responding to your question: "[...]  Begs the question of how PLA or other material is melting above the heat sink at the extruder gears when heat from the heater block is so well isolated" Chris W.'s comment covers many of the "extruder motor heat creep" problems. It's heat from the extruder motor, not the heater cartridge, that is causing upper-extruder problems. That is, I think, the answer to your begged question, is it not?

The second case, lone filament broken below the Bondtech, there are many reports of this, can be explained by simple filament runout.  I am generally inclined to go with the simplest explanation until proven otherwise.

Filament runout results in a stub of filament sticking up out of the PTFE tubing, not anything like the same thing! I wasn't referring to that at all, only pointing to an answer to your begged question.

RE: Print Plate Temperature is Never Truly Uniform

Posted by: @chocki

I'm still wondering how the Mosquito is supposed to be better in an enclosed chamber with higher ambient temperatures, maybe it maintains the slightly increased temperature in the cooling section at a more consistent level than the  E3d (Basically E3d more susceptible to environmental influences).

I think part of their magick is a more sophisticated heatbreak. From their product web page:

• The heat break conducts 85% less heat into the heat sink than a typical threaded heat break

• Composite construction of the heat break allows for the use of materials optimized for heat transfer in each section of the heat break

• Reduced heat transmission removes the need for a large heat sink

It sounds like they've incorporated the equivalent of E3D's titanium heatbreak into the base design. No idea what the "composite" is, but presumably it keeps the heat contained better than stainless steel. I'd like to see a FLIR comparison of titanium, stainless steel and this composite heatbreak. I have seen the E3D versions compared but can't find the page now.

RE: Print Plate Temperature is Never Truly Uniform

For the 85%, my guess is the tube that has the copper heat sink swaged on is simply managing material thickness (all it is used for is holding PTFE tubing, no strength needed). .  Simple, easy to make, and effective.  Heck, reading on they even admit it:

The heat break has been separated from the structural components of the hotend, allowing for a heat break that is not load bearing, and can be very thin walled. This allows for a reliable, rigid exterior structure