How often do you need to replace the PTFE tube?  

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charles.h13
(@charles-h13)
Famed Member

@luca-vicini

I use Thermal paste and recommend you do so also.  

Posted : 16/10/2020 7:46 pm
luca
(@luca-vicini)
Trusted Member

To summarise, I have problems only when I print with a layer height of 0.1mm or less.

I disassembled the hot end and inspected everything. I didn't disconnect the thermistor and heater cartridge. The only small challenge that I faced was to unscrew the heat break from the heat sink. I used the double nut trick to extract the heat break without damaging the threads.

Overall there was nothing wrong except that the thermal paste that was originally on the heat break was completely degraded (cheap thermal paste degrade after several thermal cycles). I replaced with quality silver based paste and reassembled everything placing a new brass nozzle.

Printed again the tree frog and got exactly the same under extrusion artefacts in the exactly same places.

To exclude possible filament problems I reprinted the frog with a brand new filament spool (Prosament PLA) freshly opened, checked filament diameters as well and got EXACTLY the same problems. As a side note, I place the filament spools in a PrintDry dryer while printing to avoid possible moisture problems.

I am running out of ideas here. Next thing that I am going to check:

  1. Extrusion multiplier calibration
  2. Print temperature towers, to check if there is a problem with the thermistor
  3. Start playing with the slicer parameters in order to feed more filament at lower layer heights

The frustrating thing is that on my second printer (Prusa Mini), the prints are perfect with the same filament.

This post was modified 2 days ago by luca
Posted : 18/10/2020 9:39 am
Tim
(@tim-m30)
Illustrious Member

@luca-vicini

Test wall cubes made at 0.15, 0.10, and 0.05 would be a good idea to check flow rates.  Print this in Spiral Vase mode at each DEFAULT setting:

cube-40-40-40

It might help to see one of the .gcode files coming out of your slicer. ZIP up one of the cubes and post it here.

How old is the printer?  What is the actual model? When you had the hot end apart, did you clean the heat sink, or at least remove all the plastic dust from it? Also the heat sink fan needs cleaning. Did you inspect the interior of the heat break for debris? For example, blow compressed air through it to clean out any loose debris.

Stepping back a bit. When printing 0.1 or less, does the extruder make any extra noises, like occasional clicking? Does the hot end wiggle in the extruder? The nozzle must not be able to move when you try to wiggle it - zero play. 

Have you tried printing the SAMPLE frog that came with the printer - the GCODE version at 0.05 mm [MK3_PLA_Treefrog_50um_3H_40M.gcode]?  

TreeFrog

 

This post was modified 2 days ago by Tim
It is always wise to get more than one opinion......
Posted : 18/10/2020 3:59 pm
luca
(@luca-vicini)
Trusted Member

Hi Tim,

Thanks for the great help. The consecutive clean up interventions on the hotend have improved the situation.
The printer is a Prusa i3 MK3S with the MMU2S upgrade. I bought the kit in June 2019 (the MMU2S unit in September 2019).

When I opened the extruder the heat sink was pretty clean inside I cleaned anyway with compressed air. The heat break was stuck. I had to reconnect it to the hot end, wait for the PLA plastic to melt and push it away with an Allen key. I didn't think about cleaning the fan ball bearings (will do this after printing the cubes). The extruder doesn't make clicking noises and the hot end is pretty stable in the extruder assembly.

For the test prints. I never succeeded in printing correctly the 0.05 mm TreeFrog that came in the SD card. After the clean-up I got probably the best print with that GCODE.

You can see the artefacts on the legs

For the cube, I printed successfully the .05mm. The walls are pretty good. Nevertheless the base has several defects, but I wonder if it's just a matter of improving the first layer calibration.

I am attaching the sliced GCODE for the cube at 0.05mm

Just bought a V6 Titanium HeatBreak. According to the manufacturer it is less heat conductive and should improve things

This post was modified 15 hours ago by luca
Posted : 19/10/2020 9:46 pm
Tim
(@tim-m30)
Illustrious Member

The frog looks like slight over-extrusion and assorted retraction issues. The bottom of the cube is almost certainly layer 1 or Live-Z cal. 

If I were a betting man, I'd also guess your heat break is bent. When you install the new titanium heat break, take extra care to not put any pressure on the neck. It does NOT need to be torqued into the heat sink. Snug fitting finger tight is enough - with heat sink compound - twist until it hits bottom (no wrenches/pliers needed). And, the new heat break will also remove one of the variables I fought for quite a while - the Prusa heat break MMU step.  Prusa swears the step is needed for the MMU - but others have installed the non-step version and been very happy they did the swap.

As for the heat sink: the outside fins are where time will allow dust to collect and reduce cooling capacity. Same for the fan blades. Everything in that air path needs to be kept reasonably clean to maintain adequate airflow.

All said - seems you are making progress.  

It is always wise to get more than one opinion......
Posted : 19/10/2020 10:21 pm
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