New Prusa MK3S, extruder jammed  

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Tim
 Tim
(@tim-2)
Illustrious Member

PTFE Trimming Guide:

https://manual.prusa3d.com/Guide/How+to+trim+PTFE+tube+-+Original+Prusa+i3+printers/500

MK3S is 44 mm vs 50 mm for the MK3

This post was modified 2 years ago by Tim
It is always wise to get more than one opinion...
Posted : 08/06/2019 12:58 pm
Vojtěch
(@vojtech-3)
Honorable Member
Posted by: Nick-i3mk3s

I wasn't aware of the existence of PTFE tubes with different lengths for the MK3 and MK3S, so it's possible that the one I received in my kit was the wrong length.

I'll check how far the PTFE tube is inserted in the heat break before screwing the heat sink back on.

For the exact shape and dimensions, refer to Prusa's How to trim PTFE tube guide.

Posted : 08/06/2019 12:58 pm
Nick-i3mk3s
(@nick-i3mk3s)
Eminent Member

So far I've only used the (now deformed) original PTFE tube that came in the kit, and I've verified that the hot side is properly chamfered to fit into the heat break.

Posted : 08/06/2019 1:05 pm
Tim
 Tim
(@tim-2)
Illustrious Member

Voj - I'm thinking the same ... and that shifts the heat to the gear side, which is more plausible than a hot heat sink. 

Nick - can you measure the diameter of the filament "above" the blob? The part that looks almost normal, or stick a piece of new filament next to it to see if it's 1.75 mm; or is it 2.00 mm diameter?

It is always wise to get more than one opinion...
Posted : 08/06/2019 1:09 pm
Vojtěch
(@vojtech-3)
Honorable Member
Posted by: Tim

Voj - I'm thinking the same ... and that shifts the heat to the gear side, which is more plausible than a hot heat sink. 

But this is what Nick said:

Posted by: Nick

Tim, here is a picture of the lower piece of filament that I recovered when disassembling the hot end to remove the jam:

So it was necessary to disassemble the hot-end. If I also accept that the picture is not upside-down, then  it's the space between the heatbreak and the nozzle.

 

Posted : 08/06/2019 1:12 pm
Vojtěch
(@vojtech-3)
Honorable Member

@nick-i3mk3s Where does the thick part of the removed filament come from? Which way did you pull it out of the hot-end? I think these are the crucial questions. 

This post was modified 2 years ago by Vojtěch
Posted : 08/06/2019 1:18 pm
Tim
 Tim
(@tim-2)
Illustrious Member

Voj - the fat spot isn't sized properly to be from the threaded region of the heater block.  It would be much larger: 6mm, not 4 mm. And we'd see threads. The cone is too perfect to be anything but the chamfer for the PTFE tube, too. No such angles at the nozzle interface. And unscrewing the heat break from the jammed PTFE can explain the twisted end. But it's all hypothetical ... I wasn't there. lol.

It is always wise to get more than one opinion...
Posted : 08/06/2019 1:22 pm
Vojtěch
(@vojtech-3)
Honorable Member
Posted by: Tim

Voj - the fat spot isn't sized properly to be from the threaded region of the heater block.  It would be much larger: 6mm, not 4 mm. And we'd see threads. The cone is too perfect to be anything but the chamfer for the PTFE tube, too. No such angles at the nozzle interface. And unscrewing the heat break from the jammed PTFE can explain the twisted end. But it's all hypothetical ... I wasn't there. lol.

Yes, the PTFE chamfer also explains the shapes better to me. Although I can't imagine the motor being hot enough to properly melt PLA. Soften: yes. Melt? But let's wait for Nick's answer: Only he knows for sure. 🙂

Posted : 08/06/2019 1:25 pm
Tim
 Tim
(@tim-2)
Illustrious Member

Nick - fill us in when the new Teflon arrives and you have it all back together.

When to reassemble, be sure to follow the E3D-V6 nozzle torque procedure. Crucial the nozzle and heat break are firmly butted together. Nozzle should look like this: with hex NOT tight against the heater block.

https://e3d-online.dozuki.com/Guide/Changing+Nozzles/45

It is always wise to get more than one opinion...
Posted : 08/06/2019 1:26 pm
Nick-i3mk3s
(@nick-i3mk3s)
Eminent Member

The area above the blob is still 1.75 mm in diameter as measured with calipers, although slightly twisted (probably when unscrewing the heat sink). When the heat sink and PTFE tube were removed, I was able to pull the jammed piece of PLA out of the heat break. I never unscrewed nozzle or heat break from the heater block, so these are still factory defaults.

Posted : 08/06/2019 2:32 pm
Tim
 Tim
(@tim-2)
Illustrious Member

Nick - what I can't reconcile in my brain is it seems to me the twist must on the PTFE / Gear side of the hot end - the top end of the stack.  The nicely shaped cone on the untwisted side matches with the heat break machining.  And it's the cone side filament diameter that might be helpful to know. It looks larger than 1.75mm; and if it is 2.2mm we have an answer.

But this concept is directly the opposite of what you've said.  lol 

It is always wise to get more than one opinion...
Posted : 08/06/2019 2:40 pm
bobstro
(@bobstro)
Illustrious Member
Posted by: Tim

No arguments Bob - more airflow - cooler air - can help reduce temperatures of things it is blowing across.  But I was referring to increasing flow in the heat sink helping the temps in the shaft area. The spaces are isolated by about an inch of PTFE tubing, a lousy conductor of heat.

Ah, gotcha. Yes, agreed that heat is unlikely to make it from the hotend up to the extruder. I'm just pointing out that "too damned hot" can cause a variety of problems in different parts of the printer.

I've never experienced plastic softening above the heat break transition zone.  Not to say it's impossible, but unless in an enclosure that's being heated or allowed to warm to print ABS or other plastics where ambient hits 50c+ ... I am dubious it happens.  I am also skeptical of melted PLA due to heat creeping out from the motor to the gears unless also compromised by user applied conditions like an enclosure.

That's what's so insidious about the heat issues. They can manifest in a variety of ways. As to the softening above the heat break, there were a lot of posts last year regarding the use -- or lack of use -- of thermal paste between the heat break and heatsink. Many users found adding some thermal paste made a significant difference. Again, often described in conjunction with rising ambient temps. The eye opener for me was when some users noted that ambient temps in their homes are often around 40C in the hot months, something I hadn't though about. 

Now that you mention it, I don't know that actual heat transmission along the extruder stepper motor shaft has been positively identified as the issue. "Extruder motor heat" is a common complaint, and that might just be contributing to overall heat. Reducing aggressive retractions, and simply awareness of MVS helped many users.

Other factors also seem to add to the mix. There were a spate of problems caused by the lack of a collet on the hotend causing PEI tube shifts for some users. Again, heat might have increased friction, contributing to the problems. I going to watch for the spike in temperature-related problems around July-August.

[...] I read an article or blog, I think it was on the E3D or MicroSwiss, could have been elsewhere, where they talked about the heat break transition zone, and how plastic can't really melt above the neck because of the design: 40w simply can't push that many calories up the thin stainless neck material, especially with a heat sink attached, as long as there is minimal air flowing over the heat sink.

I think that "air flowing over the heat sink" is a big part of it, combined with ambient temps. Add in people putting fancy fan covers on, enclosures, lack of thermal paste between the heat break and heat sink, and things like dust filters that increased friction along the filament feed path, and it's a cascade of possible consequences.

I've been fortunate in that moderating MVS and keeping an eye on retractions has resolved any extruder skip issues I've had on my OG Mk3. Then again, ambient temps in New England aren't outrageous. I might have a different experience if I still lived in Phoenix.

My notes and disclaimers on 3D printing and miscellaneous other tech projects
He is intelligent, but not experienced. His pattern indicates two dimensional thinking. -- Spock in Star Trek: The Wrath of Khan...
Posted : 08/06/2019 6:44 pm
Nick-i3mk3s
(@nick-i3mk3s)
Eminent Member

Tim, I just received the piece of PTFE tube from Ebay, and shaped it according to the link you provided (44 mm, inside conical cut with a drill bit, outside conical cut with a pencil sharpener). It fits perfectly, but it does not lock in place even though I have the black clip inserted into the heat sink. Perhaps the diameter of the PTFE tube is slightly smaller than the original? When measured with calipers it's exactly 4.0 mm outer diameter though.

Anyway, I replaced it and followed your recommendation to lower the room temperature, and placing the printer next to an open window. Room temperature is now 18°, and extruder motor temperature is 42° as measured with an IR thermometer. It appears to be printing fine for the time being (black PLA, 215° extruder temp). When/if it fails again, I'll post back with the symptoms and more pictures.

Posted : 15/06/2019 3:43 pm
Tim
 Tim
(@tim-2)
Illustrious Member

If that PTFE is free to move up and down, it will more than likely haunt you. I also measured the PTFE spares for my MK3 (from Prusa), they measure from 3.90 to 4.01 "diameter".  If your 4.00 mm PTFE isn't locking, perhaps the collet itself is bad? 

It is always wise to get more than one opinion...
Posted : 15/06/2019 8:26 pm
Nick-i3mk3s
(@nick-i3mk3s)
Eminent Member

That's possible, because I had to apply a lot of force to the collet to get the deformed PTFE tube out of the heat sink.

I know I'm asking for a lot here, but would you happen to have a part number for the collet, or a manufacturer link?

Posted : 15/06/2019 8:39 pm
Tim
 Tim
(@tim-2)
Illustrious Member
Posted by: Nick-i3mk3s

That's possible, because I had to apply a lot of force to the collet to get the deformed PTFE tube out of the heat sink.

I know I'm asking for a lot here, but would you happen to have a part number for the collet, or a manufacturer link?

I'm not 100% on this, but you can ask E3D tech support for what you need.

https://e3d-online.com/embedded-bowden-collets-for-metal-1-75mm-filament

It is always wise to get more than one opinion...
Posted : 15/06/2019 9:04 pm
Nick-i3mk3s
(@nick-i3mk3s)
Eminent Member

Update: it appears the collet that holds the PTFE tube in place does not matter at all, I've been printing for a few days now, and so far the MK3S prints perfectly even though the PTFE tube is free to move up and down in the heat sink (although in reality it's constrained between heat break extruder motor wheel).

For reference, I got replacement PTFE tube from Ebay: https://www.benl.ebay.be/itm/PTFE-Tube-ID-2mm-OD-4mm-for-1-75-Filament-Makerbot-Prusa-Mendel-3D-Printer/161868367103

Posted : 18/06/2019 7:35 pm
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