kris

Absolutely. Will show the results here soon.

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.

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.

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.

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

@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?

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

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.

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?

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)?

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

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.

My interpretation of what the filament might look like under retraction. It might end up doing some kind of 'pumping' motion.

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

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.

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

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...

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

Yep :-P

That is true. Maybe one reason why I should stick to ABS.

I am afraid I did not take any pictures of the process, so I will try to explain in words. First I removed the four long bolts at the top that hold the extrude together. That can be done without tools. Then you remove the side fans and the little screws that hold together the bottom aluminium part to which the nozzle is attached. Then you need to heat up the nozzle to >200°C. With the hexagon key you can now unscrew the ring that holds the nozzle in place (the one with the holes in the side). You can also do that with a hexagon key. Be careful not to touch the hot parts. I used a pair of flat nose pliers to hold the brass part. The nozzle can now gently be pulled free from the aluminium frame. Regards, Kris

Hi everyone, I would quickly like to share with you how I managed to get rid of underextrusion on my UM2. This first happened to me in the middle of a print. I then tried standard prints that used to work fine, so I could rule out Cura as a possible failure source. Then I tried every method I could find on the forum; the 'atomic' cleaning, readjusting the material flow, taking apart the extruder wheel. It seemed as if material was supplied to the nozzle just fine, but in retrospect the material that left the nozzle looked very rough. Nothing would help. I finally took the entire extruder apart and soaked relevant parts in acetone for a few minutes, cleaned everything with a q-tip, soaked, cleaning etc. After 20min or so the parts were completely clean again. Now the prints look exactly the way they did when I first received the machine. Sounds easy, but I would not have though that the performance of the extruder would deteriorate over time to the point where it needed to be cleaned. This is probably the regular maintenance the machine requires in order to function properly. Another theory is of course the contaminated filament. This happened while using white ABS from UM. A few days prior to the incident I found a huge piece of something very hard in the filament. If you miss something like that, it ends up in the nozzle. Anyway, next time I experience underextrusion, I will again give the extruder a good acetone bath :-P . Regards, Kris

Better picture:

Hi all, @ Wallan: Maybe with your approach you basically achieve the same effect: You control the temperature to get an even temp distribution by simply turning off the heated bed. I did read about the ABS 'slurry' but was hoping to find a way to set may process parameters to get the print under control. @Jonny: I hope I understand stringing correctly, but I think I had that from the start. But by reducing the material flow (tried 91%-86%) I managed to completely get rid of that. Attaching an image, hope it is visible. The image shows the printed surface.

Hi everyone, I have been struggling with warping over large and thin ABS structures for some time. I did try out many possible countermeasures that I found on the internet or that I came up with by myself. But nothing really worked. Although I managed to reduce the effect somewhat, I started to loose hope that the problem can be totally overcome. But yesterday I managed to make a first print that is totally warp- free. Here are my findings: The main problem of warping is the non uniform cooling of a part that will result in internal stresses and thus deformation. I am using the UM2 with a heated bed. I found that warping will reduce with increased bed temperature, but 100°C is a maximum for the bed. A brim will help to stick the component to the bed, but will not do anything against the cause of warping. At some point even a brim will fail and stress concentrations at corners will make them peel of. With increasing height of the component temperature will decrease and stresses will arise. So I covered the top of my UM2 will a simple cardboard box with a cut out for the filament hose. I also covered the front with cardboard. Increased the temperature of the bed to 100°C and turned of the two cooling fans in Cura. I also used Cura 14.03 TEST2. That didn't help initially, I just found that the gcode size reduced by 50% in size compared to 14.03. I was a bit worried that the temperature could be too much for the internals of UM2, but the bottom section keeps pretty cool. After the print I am letting it cool down for a while. For the adhesion to the glass plate I am using the glue stick supplied with UM2. I think key is the uniform temperature (low gradient) inside the build volume. The structure I printed is a 0.8mm thick shell and minimum 40mm high and about 200x30mm at the base. I used the black ABS from Ultimaker. Anyway, the result: No warping at all. I am now planning on building a plexiglas door and roof to better control the internal temperature. I think I will also install a few temperature sensors for monitoring. I addition I reduced material flow to 86%, there was a little overextrusion. Now with 0.1mm layer height I can hardly make out the layers. Regards, Kris