PSA - Check your PTFE tube length!
I'm hearing more and more reports of people getting their mini with the installed PTFE tube being too short by a millimeter or more (myself included). This can eventually lead to the dreaded underextrusion issue. The spare PTFE tube is often the right size. The tube should be 43.4mm +- 0.1mm.
RE: PSA - Check your PTFE tube length!
I had exactly the same thing. It's weird that the installed tube is short, yet the spare is usually the right length... I would hope Prusa use a cutting jig or an automated machine to cut the tubes. It seems more likely that the PTFE is creeping over time.
RE: PSA - Check your PTFE tube length!
I don't think the installed tube is shorter from the factory. I noticed the same thing and replaced it with the spare, after several days of prints I began to experience extrusion problems again. When I disassembled and checked the second PTFE tube length, it was also shorter. I believe that it deforms due to compression and heat. It's a flawed design.
Prusa Mini Silicone Bed Leveling Mod: https://bbbenji.github.io/PMSBLM/
RE: PSA - Check your PTFE tube length!
I could be that the PTFE tube has been stretched under manufacturing, cut to right length by Prusa, but returned to "original shape" under heat. PTFE is not a form stable material. It will deform under pressure.
Haven't tried it, but loosening the three grub screws in the cooler should allow the stainless tube to move a little and compensate for the shorter length.
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RE: PSA - Check your PTFE tube length!
I've put in the new tube and will report back later to see if there's any shrinkage
RE: PSA - Check your PTFE tube length!
I was in the pool!
RE: PSA - Check your PTFE tube length!
@strigusconsilium
I've had my Mini for about two months now can also confirm that the hotend PTFE tube slightly shrinks over time. I don't have a picture of the stock PTFE tube that came pre-installed, but I know I measured it and it was initially to spec (43.3mm-ish). I've recently had some minor under extrusion problems after a retraction and decided to remove the PTFE tube to examine and noticed that it measured 42.6mm.
Besides the under-extrusion after a retraction, I haven't had any other noticeable problems. I've also followed the recommended instructions to loosen the three grub screws and push the hotend up a smidge before tightening the screws back up. I also made sure to readjust my MINDA probe height so it's about 0.8mm away from the the bed.
For now, I replaced the stock PTFE tube with the extra included with the Mini.
RE: PSA - Check your PTFE tube length!
I think we must just have to live with this and make part of our maintenance routine.
I posted about this yesterday:
In my case, I had problems early on.. Replaced the PTFE beacuse it was 1mm short.. Its been fine for months and now my print problems have happened again.. Last night I checked the PTFE and again, its 1mm shorter.. So i have changed it again and all is good once more.
I just think the pressure of how its assembled combined with heat just compresses it down to a point where it no longer makes a seal.
I don't mind changing it as its an easy, 5 min job.. What I don't like is the Z axis re-calibration on TWO different thickness sheets after..
I wonder if there is a different material which could be used which does not strink.. My replacement last night was cut from my stock of PTFE and its slightly less translucent and a tiny bit thicker.. So I am wondering if its will be any more or less resiliant? I guess time will tell.
RE: PSA - Check your PTFE tube length!
There is a material called Torlon that is heat resistant and form-stable. It is more expensive compared to PTFE.
Some time ago I saw it mentioned as a replacement in the MK3s + MMU2 combination for the 1.85 mm PTFE tube in the extruder. I tried to find a reseller for 4 mm rods, but gave up...
The idea was to replace the bottom part (hottest) with Torlon and keep the top part in the usual PTFE.
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RE: PSA - Check your PTFE tube length!
I think we must just have to live with this and make part of our maintenance routine.
...
I wonder if there is a different material which could be used which does not shrink..
Well, all metal hotends are well established technology, there's no need to re-invent the wheel. People stopped using plastic in the hot end for very good reasons. I don't why Prusa went in the direction they did.
RE: PSA - Check your PTFE tube length!
PTFE, or 'Teflon', does in fact cold flow under pressure... that's why it makes a great seal material in joints which are closed, like Boss o-ring fittings or washer faces with a groove. I image the tube 'shortening' is exactly this... put it under pressure, give it a little heat, it's gonna deform for sure.
Glad I saw this, this must be why after about 300 hours of printing, I'm getting some stringyness and weird behavior.
RE: PSA - Check your PTFE tube length!
Seems I've also run afoul of this issue.
I thought it was any number of things before I came across this post. I even started a thread about the issues I was having: https://forum.prusa3d.com/forum/how-do-i-print-this-printing-help/horrible-nozzle-clog/
By the time I found this, I had already discovered the installed tube was about 1mm short, and swapped it for the replacement. Just this morning, it clogged up again. I've checked the replacement tube, and it is also about 1mm short now (it was fine when it went in). This was only a day ago. (I should also point out that my Mini is only about two weeks old).
Obviously there is a limit to how much one can move the heat-break tube up to compensate for shrinkage of the PTFE. Does anyone know if it will stop shrinking eventually?
RE: PSA - Check your PTFE tube length!
Seems I've also run afoul of this issue.
I thought it was any number of things before I came across this post. I even started a thread about the issues I was having: https://forum.prusa3d.com/forum/how-do-i-print-this-printing-help/horrible-nozzle-clog/
By the time I found this, I had already discovered the installed tube was about 1mm short, and swapped it for the replacement. Just this morning, it clogged up again. I've checked the replacement tube, and it is also about 1mm short now (it was fine when it went in). This was only a day ago. (I should also point out that my Mini is only about two weeks old).
Obviously there is a limit to how much one can move the heat-break tube up to compensate for shrinkage of the PTFE. Does anyone know if it will stop shrinking eventually?
Even if it were to stop shrinking, the hot end will eventually become deformed.
RE: PSA - Check your PTFE tube length!
What about the Bondtech heatbreak? PTFE does not go all the way to the nozzle but down to the heatbreak (duh), what are the chances of it deforming? The temperature should already be a bit lower there.
RE: PSA - Check your PTFE tube length!
What about the Bondtech heatbreak? PTFE does not go all the way to the nozzle but down to the heatbreak (duh), what are the chances of it deforming? The temperature should already be a bit lower there.
I'm only guessing here but I suspect the PTFE tube in the Bondtech heatbreak doesn't suffer from this issue for that reason.
RE: PSA - Check your PTFE tube length!
I have a theory (completely untested at this point), but I'm wondering if this may be caused by insufficient (or poorly distributed) thermal paste between the heat-break tube and the heat sink.
My reason for thinking this: As I posted earlier, I swapped my PTFE tube for the spare, and it lasted less then a day (~4 prints). When I swapped it, I had the heat-break tube completely removed to clean out plastic from the inside of it. Through doing this, even though I was being as careful as I could, some paste was lost to my hands and tools. Since I don't have any more (I've ordered some now), I hoped what was left would be enough. And then it clogged again only a few prints later.
I suspect that if the heat-break is not cooling to heat sink correctly, the PTFE tube gets too hot, and shrinks more or faster than intended.
Like I said, just a theory. I'm cleaning it all again, and then will have to wait for my thermal paste before I can put it back together and try it out.
RE: PSA - Check your PTFE tube length!
my experience with the Bondtech heatbreak is that it too suffered the same shrink problem. I got the same extrusion error after installing it and ended up using a slightly longer ptfe tube than the one they supplied. I also did apply the thermal paste thinking it was a heat creep issue.
RE: PSA - Check your PTFE tube length!
I had the same issue, and I was not the only one (posted here: https://forum.prusa3d.com/forum/general-discussion-announcements-and-releases/retracting-and-clicking/paged/2/#post-219513 ).
I have a little more than 1 week, and it's working finr after changing to the spare PTFE tube (and readjusting accordingly to prusa help page). I hope it will not be needed to readjust the heatblock too often ... 🙂
RE: PSA - Check your PTFE tube length!
we had the same thing happen except our spare was to short as well!! finally replaced PTFE tube with correct size, but our prints are still hit and miss. sometimes they are good, sometimes they are bad. we are very frustrated with the mini
RE: PSA - Check your PTFE tube length!
Would stronger fan help? Providing there are bette fans at this size.