Bulges in PTFE tube
I have replaced the hotend assembly on my MK3S+ after I have had PTFE tube jams. However the problem has recurred with a completely jammed filament in the PTFE tube. I'm not sure why this is happening though I have read and noted some of the posts on this subject and taken possible advice.
In general, my prints are of model trains at the finest detail and thus I use a 0.2mm nozzle and very thin layers. I have used the standard finest settings supplied by Prusa and have adjusted retraction.
Taking apart the hotend and removing the PTFE tube, I notice that there are bulging rings on the outside of the tube which makes me think that the tube is being compressed when the hotend is reassembled. I have noted the positions of the nozzle, the heatbreak and the entry point of the tube below the Bondtech gears and as far as I can tell, they are normal. Is there a reason for the bulging and is this the cause of my filament jams?
BTW, I am a Forum virgin so I hope I have got this right!
RE: PTFE
If the PTFE tube has bulges, replace it. It certainly could cause jams.
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Chuck H
3D Printer Review Blog
Bulges in PTFE tube
If the PTFE tube has bulges, replace it. It certainly could cause jams.
Yes replacing a tube is what I have done - several times - and now I have run out of stock! (More on order.) However, I am trying to determine the cause so I can stop or at least reduce the number of failures. I have the feeling that the tube gets crushed at reassembly, possibly because the heatbreak or heatsink are not adjusted correctly. I have never tampered with them on from the factory supplied units. The other possibility I can think of is that using a 0.2mm nozzle is causing too much back pressure though I am using the ultrafine Prusa defined settings for a 0.25mm nozzle.
45 degree angle cut every time you insert filament
The little blob on the end of the filament when you do a color change, run-out, etc needs to be cut off each time. Inserting the blobby end of a prior roll will ruin your PTFE tube over time.
Bulges in PTFE tube
The little blob on the end of the filament when you do a color change, run-out, etc needs to be cut off each time. Inserting the blobby end of a prior roll will ruin your PTFE tube over time.
Yes, I do cut off the end of the filament before inserting. This is not the reason for the bulges. I have run filament through brand new tubes just to check there isn't a problem here.
Incidentally the bulges in the two tubes I have looked at carefully before discarding show an external bulge ring at approx. 1cm from the bottom of the PTFE tube (at the heatbreak?) or just under 1cm from the top.
Tony
Bulges in PTFE tube
I have been investigating my problem and I think I have cured it. Time will tell.
I think the heatbreak was (hopefully now isn't!) too high in the heating block as my nozzle was tight against the block rather than a gap. I suspect excess pressure on the PTFE tube caused the bulging rings around the tube.
I have found that molten filament was all round the heating block which means there was a leak. This is described in the manual.
To cure my problem, I disassembled (again) the hotend, heated it and removed the heatsink, heatbreak and nozzle. I carefully cleaned (masses of) molten PLA off the heating block and everywhere it had spread (e.g. the wiring). I then screwed in the nozzle using a feeler gauge to get 0.5mm clearance between the heating block and the lip of the nozzle. I then screwed in the heatbreak tight against the nozzle - well as tight as possible without damaging the heatbreak threads. hopefully any residual molten PLA will have been squeezed out to make a leakproof seal. I then replaced the heatsink, PTFE tube (this time undamaged). Then I allowed hotend to cool down and re-assembled the hotend into the E-Axis assembly. After full calibration, I went ahead with an 8 hour print which the printer performed flawlessly.
This morning, however, I started a 2+ hour print and that failed after approx 30 minutes with no filament flow. The extruder was clicking on retraction which made me think this was a recurrence of the problem. However unloading the filament was without problems so I think the PTFE tube was OK. I examined the hotend for leaks (none found) and other clues. I think this problem is due to the tension applied to the filament as it passes through the Bondtech extruder mechanism. I have tightened the screw to give more pressure on the filament and I am thinking that my original setting allowed slippage of the filament. The printer has now been running for about an hour with no problems.
I looked at the MK3S+ E-axis assembly manual chapter 34 for the tensioning adjustment and did not find a definitive setting. Although I suspect the tension may differ for different filaments I am wondering how to determine the optimum tension on a filament?
Tony