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kris

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Everything posted by kris

  1. kris

    STL Dateien mixen

    Zum bearbeiten von STL Dateien bietet sich auch Meshlab an. Dann einfach mal nach Meshlab und 'join meshes' googeln. Gibt zahlreiche gute Tutorials auch bei Youtube.
  2. You might be correct. Would be interesting to try this out.
  3. My guess is that the current heat sink is in the wrong place. It is not efficient in preventing heat moving into the PTFE part. It is also too far away.
  4. I think if the heat sink touches the aluminium block that is not a bad thing. This just increases the cooling area. Neglecting the rear fan is kind of conservative I guess, since it will improve convection. Now that I think about it, I do not really understand the slotted aluminium block at the back. To me it seems as if it is too far away from the heat source. I think the new heat sink could replace that component completely and reduce temperature in the upper part of the extruder considerably.
  5. Here are the results. I ran a few different models to test out different ideas to knock down the temperature in the PTFE bushing. I did not take into account forced convection (from the fan). I achieved the best results with a heat sink at the top, as originally proposed. In addition reducing the contact area between the PTFE bushing and the remaining components helps. I managed to reduced the temperature in the bushing from 170°C to 110°C (model ptfe_v2_p). I measured the temperature a few millimetres away from the interface to the nozzle, because here the temperature is pretty much unchanged due to the proximity to the heat source. I have tried not to alter existing components, in an attempt to create a method that can be retrofitted. Currently the heat sink that I added does not fit into the setup. There is too little space. So it has to be reduced in size somewhat. Important to note: The TG of ABS is around 104°C. Previously we were well above that in the PTFE bushing which means the ABS will loose most of its mechanical properties before it even enters the nozzle. At the moment the spring pushes the bushing firmly against the nozzle. There will be a certain heat transfer. If we would allow for a little gap between these components the temperature in the PTFE bushing will remain around 100°C. See below. Not sure if that would create other problems. But sure worth a try. The bushing would have to rest against the steel nut. Feedback is most welcome
  6. Absolutely. Will show the results here soon.
  7. Yes, you guys are correct. The idea was basically to pull away heat from the PTFE component. PTFE has two advantages; it has low friction and it can handle high temperatures. A significant drawback is the thermal expansion which might cause under extrusion. My hope is that we can overcome these trouble with minimum effort, i.e. without replacing existing parts. I have hence added a heat sink in the analysis in an attempt to draw heat away from the PTFE. And it seems to work very well. I will post the calculations here in short while. Have a short business trip tomorrow. That heat sink is just an add on that will not require any changes to the existing components...I hope :???: I think that ultimaker's initial intention was to use the aluminium structure of the extruder as heat sink. That is the reason for the 3rd fan I guess, in order to improve convection. But apparently it is not efficient enough in doing so. What do you think, I might be wrong here.
  8. Maybe if there was a heat sink before the nozzle meets the PTFE fitting. This way the heat could be led away from the fitting. Friction would most likely increase.
  9. me neither :???: My hope is that existing parts can me modified and optimized to overcome the problem. Apart from under extrusion I am very happy with the UM2.
  10. That E3D hotend looks great. There are a few things that stand out: 1.There is very little material connecting the actual hotend with the upper part that meets the bowden tube. Thus heat flow to the upper part will be limited. 2. The upper section has additional large cooling fins 3. All metal means that there is limited and uniform thermal expansion throughout the design
  11. @3poro: adding additional heat sinks would probably help to reduce the temperature. The effect could easily be measured. Using the space for the second extruder for the heat sink is a good idea. Does anybody know if UM is trying something like this already? @EldRick: I noticed your post. Do you know if there is a measurable effect?
  12. I think convection is not doing much to cool the PTFE fitting. A heat sink that leads away heat from the part is far more effective I guess. Maybe using heat transfer paste between the aluminium parts of the extruder helps a bit? Or adding another small heat sink at the front. Another stupid idea; Could the flow of the middle fan be reversed? At the moment it blows warm air from the heat sink onto the PTFE fitting. I think the PTFE fitting is getting bigger and bigger because it gets filled with PLA/ABS which will prevent it from contracting back to its original diameter. And it will work its way up through its metal casing. The spring will not be able to push it back. A gap will form between the fitting and the nozzle. Yes, black anodization might help as well. As so often, a combination of improvements might give us the results we are looking for. The simple things can be tried first. Any chance the guys from UM could try this? Maybe they already have :-P
  13. Here are a few results for a tightly fitted PTFE bushing. Not sure if it would work. Thermal expansion would most likely create a larger force upon the remaining structure compared to the used spring. If the structure can handle it, there is no problem. If not, the wall thickness of the bushing could be reduced. To account for thermal expansion the inner diameter has been increase to 3.4mm . The results; the bushing does not overlap the brass fitting anymore. The hope is that resistance for the filament, especially under retraction, is reduced.
  14. I had exactly the same problem. Nothing would help, except taking the extruder apart and cleaning it with acetone. http://umforum.ultimaker.com/index.php?/topic/5929-possible-countermeasure-underextrusion/ This will only work for ABS, as I have been told. And it will take a while, but I think it is worth the effort. A possible cause: http://umforum.ultimaker.com/index.php?/topic/5953-idea-on-underextrusion/ At least my theory :-P If the temp sensor is broken, shouldn't there be an error message?
  15. Got some results from the calculations. Actually very interesting ones. I now added the appropriate heat transfer properties so the model should behave pretty accurate. My analysis does not take into account the rear cooling fan, so the temperature on the top of the PTFE fitting is too high. But still, here is what I got. First temperature plots (in Kelvin): The PTFE bushing will expand inwards and upwards, leaving a little gap between the brass nozzle and the bushing itself (as Anders described above). I do not know what the gap does over time. But I tried doing a time lapse video of the PTFE bushing while heating up. That didn't work, but when examining the photos I noticed some marks that look as if the bushing has moved several times in vertical direction. It also looked as if the bushing moved up slightly, but very hard to tell. And this would be my current theory on what happens after multiple retractions: The inner diameter of the bushing decreases from 3.2mm to 3.0mm due to thermal expansion. Material will accumulated between the nozzle and the bushing. Retraction behaviour will become very unpredictable. Maybe the filament is even torn off above the interface. If air is pulled into that gap, that air will get pushed out the nozzle at some point. I noticed that when I had underextrusion, the material would come out very uneven. The same amount of material will leave the nozzle, but it will be mixed with air (or at least voids). So my best guess so far is that underextrusion is mainly caused by the nozzle itself in combination with retraction. Performance will deteriorate over time due to the material accumulation. This also explains why the problem can occur anytime and only a complete clean will help. A possible countermeasure could be to increase the hole in the bushing to account for the thermal expansion, i.e. 3.4mm. I would even try this if I had a spare one. Maybe we could loose the spring as well (see v3 below)?
  16. Hi Anders, Your post made me think: The teflon piece will expand due to the increase in temperature. It is constrained by the metallic bushing, the only direction in which it can move is upwards. By doing so it has to push against the spring. But due to the thermal expansion it will probably generate a force which exceeds the force generated by the spring. A gap will form, as you have described with your first picture. I will see if appropriate boundary conditions in my FE model will let me show this. I think if we would take a video of a freshly installed teflon piece and raise the temperature, we would also be able to detect the movement under a time lapse. Regards, Kris
  17. I am not really sure what you mean. If I heat up the nozzle I can also push through the filament manually. I have so far only applied a constant temperature to the entire setup, because it is easier to simulate. The heat is however only generated by the nozzle. I will try to redo the calculation to see what the temperature gradient is. Regarding your last comment; the teflon part does have a tight fit and the casing prevents it from expanding outwards. But as the simulation has shown, the inner diameter will decrease instead. The piece will expand inwards. To me that seems even worse.
  18. My interpretation of what the filament might look like under retraction. It might end up doing some kind of 'pumping' motion.
  19. Hi Aaron, All in all my boundary conditions are very simple for the first analysis. I didn't measure the force from the spring. I simply assumed that it holds down the coupler perfectly. I also used a uniform temperature distribution on the coupler. I just redid the analysis with the major components of the extruder included (and a contact algorithm betwwen those components). In addition to expanding on the top, the PTFE coupler will expand inwards further down. Here it has nowhere to go because it is held together by the metallic nut. The channel diameter for the filament will decrease from 3.2mm to 3.0mm. I cannot say if this has any influence on the performance of the extruder. But if the filament assumes the form of the expanded coupler, it might experience a form fit with the coupler. This could potentially be a problem during retraction because the feeder will not be able to pull out the front part of the filament. Pressure on the nozzle with be reduced, but the behaviour of the filament might be very unpredictable after that. Regards, Kris
  20. Maybe the teflon could be restrained by an outer coat of aluminium to prevent it from deforming. Need to do anthother analysis, when I get the time.
  21. Hi everyone, I have got an idea that I would like to share here, again on the topic of underextrusion. I did not think it all the way through but figured it makes sense to share it anyway. I remember that my underextrusion started in the middle of a print and from what I have understood and read on the forum this is what happens mostly. Part of the extruder (Part Nr. 1309-Z2P-B) is PTFE. I also recall that PTFE, or Teflon, has a very large coefficient of thermal expansion. So I downloaded the files and did a quick FE-analysis of the piece under temperature. I am attaching the results for everyone to examine. I guess teflon is used to reduce friction. But to me it looks as if the deformation might cause a wedge shaped filament. The feeder might have serious trouble pushing that material down the nozzle, especially if it cools partially. Regards, Kris
  22. I thought about that too. But I figured that the cotton fibres are far too small and thin to get caught in the nozzle. And whatever I tried, nothing else would help. After a while you just do not care any more. Anyway, although the methods works to clean the nozzle, it does not eradicate the cause of the irregular extrusion. But I believe these guys were on to something: http://umforum.ultimaker.com/index.php?/topic/3976-almost-always-missing-layers-underextruding/page-2 As far as I have understood the extruder design suffers form a design flaw. Seems as if turning of retraction helps...
  23. plus the round piece with the holes in the side. I put a small cup of acetone on the build platform and raised it, so I could soak the nozzle without having to detach it from its cables. Didn't want to damage those. I removed as much cotton from a cotton bud as I could to it would snuggly fit into the nozzle while turning it. I did this several times until nothing would come out anymore. The nozzle needs to be soaked a few times since the acetone will vaporize quickly. Regards, Kris
  24. That is true. Maybe one reason why I should stick to ABS.
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