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Good catch. I set mine to zero because I have never had my filament grind to dust (on the UM2).

If you ask nicely, UM will give you a free second nozzle. Offer to pay for it and they will likely refuse your money. Step 2 is to modify the nozzle for .25mm opening - maybe talk to a machinist or go to a local fablabb or makerspace and see if you can maybe solder the hole closed and then drill it out again. I have 2 nozzles for my UM2: .4mm and .7mm Unfortunately it is not easy to swap - it takes 20 minutes or so although I get faster each time.

Nice excel graph. It would be interesting to also include layer time - Cura simply assumes 100% acceleration and determines it based on print speed and total length of all lines on a layer. Again: Did you hover over the settings in Cura? It explains how this works. Again: For PLA you should be using 100% fan for min and max. For ABS, lower fan speeds make more sense. To answer your question - if you hover over the "max" fan speed it says it increases fan speed to MAX value as layer time adjust speed by 200%. I think Daid means 50%. So the point is that as print speed approaches half of nominal speed, fan speed should approach MAX speed. You could test this by starting the print with a higher print speed and then graphing it in excel again.

On my brand new UM2, 4.5mm (the default) wasn't enough. It needed more like 5.5 or 6mm. 5.5mm was enough for me. After I secured the bowden better (a month or two later) I was able to reduce that to 4.5mm. Try increasing your retraction a bit. Also for some filaments I have to lower the temp to 190C to eliminate stringing but that may mean printing even slower. Although usually 210C is plenty cool enough. Also make sure your travel speed is fast - 150mm/sec minimum - try 250mm/sec. This helps break the thread/string. Moving at 250mm/sec is not a problem for pretty much any 3d printer out there - it's the acceleration where the UM is so impressive.

Definitely remove the 4 long thumbscrews first. Changing the fan is the easiest thing to do on that head. Easier than messing with the nozzle even. To see the fan connector you don't even have to do that, just slide up the black mesh and you can see all 3 fan connectors in there. When removing the 2 screws holding in the heatsink be careful as the spring in there (it's obvious) is pretty strong so squeeze it together with one hand while removing the 2 screws with the other. Click "raw" to see the um2 assembly manual: https://github.com/Ultimaker/Ultimaker2/blob/master/um2%20assembly%20manual%20V1.1%20_english.pdf

Could be lots of things. The first thing that comes to mind is that the first layer or two are printed slower. What speed are you printing at (the speed isn't important - it's the volume of PLA per second - so whats the layer height and speed)? And what temperature. It's easier to get filament out at 240C than 220C. Don't say "defaults" as these can change among firmware versions, plus the defaults in "quick print" for example also change between versions, plus I've changed settings so many times I don't know what the default used to be anymore. Have you printed many things before this started? Are you near the end of a reel of PLA? The second thing that comes to mind is tangled, difficult to deal with, sharp curvature filament from the end of the spool. The 3rd thing that comes to mind is clogs - but this doesn't sound like a clog as with clogs it usually only prints a tiny bit each time - maybe for 20 seconds. Not a whole layer. 4th: filament diameter might be 3.00mm instead of 2.85mm. That would cause this. 5: Printing at or below 180C would cause this. 6: If the 3rd fan on the head is broken - that could explain this - it should start spinning when you power on the machine (even before the lights come on) - it's quiet and most people don't notice it - it's at the rear of the print head.

Unlike normal motors, stepper motors apparently use the same amount of current regardless of how much work they are doing. So I assume a hot motor doesn't have much to do with mechanical resistance - more to do with current setting. These stepper drivers are very easy to destroy. But they are also cheap and available from many sources.

Yes. Mechanical issues look different - typically two close together lines and then a gap and then repeat. Better to print slower. Are you sure these gaps aren't on purpose by the slicer? Maybe open the gcode in repetier host (it's free) and see if it also thinks there are expected gaps?

I recommend .2mm layer height and 100% fan both of which help with bridging.

@selmo there are many causes for missing layers. If the model is manifold (that's a HUGE IF as it is difficult to prove) and if there are no walls that are inside the STL closer together than .8mm then there are still several other things that can cause this. It's hard to explain so I'd rather you sent me an STL with issues. For models that are organic - like sculpture the problem tends to be (somewhat) related to your triangles being too small. For mechanical or architectural models it tends to be that walls or corners are too close to other surfaces or corners. Part of what cura does is it intersects a plane with the STL and gets a bunch of line segments in no particular order. This is important: NO ORDER. STL doesn't specify which triangles are touching which. So then Cura takes this random ordered set and tries to link all the lines up. Sometimes it links them up wrongly because they are very close together but not quite and Cura decides "close enough". This causes problems as Cura gets chains of lines that refuse to form loops and so it just discards those and prints nothing.

@ultismoother - you frustrate me. POST PICTURES PLEASE! I asked you several times. Also you don't understand what I am saying about wall thickness. I have seen the problems you talk about. They can be from several known causes. I refuse to say anymore until you post pictures. Even better send me the STL.

Strange. Well that nut with the holes in it rotates - you may want to heat to 180C before rotating - you might even have to disassemble enough to get the spring out to lessen the pressure. Rotating that nut (which is not as strong as steel so take it easy!) raises and lowers the nozzle tip so that if we ever go dual extruder you can set them to the exact same height.

I assume this manual will tell you how to assemble it. I really didn't pay attention to the wires other than to make sure the fan wires didn't get pinched. The manual might not be helpful - I haven't looked at much of it yet: ultimaker2 assembly manual - click "raw" to download the pdf: https://github.com/Ultimaker/Ultimaker2/blob/master/um2%20assembly%20manual%20V1.1%20_english.pdf

This sucks. The worst thing about it is it may take a while to get a replacement - if it was me I would PM sander and send him to this thread and give him your ticket number - this is urgent because your printer is useless until you get a new nozzle - the sensor you might be able to order or build but the nozzle is cusom. http://umforum.ultimaker.com/index.php?/user/423-sandervg/

Some day you will damage your bowden with the 4 blades in the "bowden holder" and it won't stay up any more. Only when that happens should you cut off a few mm of the bowden. But the bowden holder will still "stick up".

First layer looks good, second layer has unexpected gaps. Is your infill set to 70% or something? Did you change flow to less than 100%? Some people have overextrusion on first layer and fix it by lowering flow to 90% instead of lowering the bed by 10% of the first layer thickness. This looks like typical underextrusion on a UM Original, but underextrusion on the UM2 tends to have sudden slip backs of the feeder such that you have obvious spots where there is zero extrusion. This more looks like something on purpose such as the first two things I mentioned.

Double check that the filament doesn't have a notch in it where the feeder ground it up. Other than that it could indeed be the nozzle. Here is the easiest method to unclog the UM2 known as the "atomic" method: http://umforum.ultimaker.com/index.php?/topic/4118-blocked-nozzle/?p=33691

The people who complained the most about the slice button actually had an issue that made the UI lock up (I think mostly on MACs). Leaving out the button was good because it highlighted bugs that would have been missed if Daid added the button and Daid fixed them relatively quickly.

Don't know. Some ideas: 1) Is the fan blowing on the nozzle tip? That can cause underextrusion if it blows directly. I mean could this have changed since a year ago? You didn't show that in your photographs. 2) Maybe the sensor probe is bad - calibrate temperature by heating to 95C and 105C and it should boil at 105C and not at 95C. 3) Do you print ABS sometimes? Switching back and forth can cause clogs. 4) Maybe there is some wood from the feeder getting onto the filament and getting carried through the bowden and causing clogs although likely this would be more serious. I recommend this test to help decide if the feeder is the problem: http://umforum.ultimaker.com/index.php?/topic/4222-pulling-force-of-um-extruder/?p=34887

I still have the original "origami" shroud. It was damaged so I repaired it with kapton tape and it works great. Kapton tape can touch the head and not melt.

It's normal that it's always on. It's not normal that it is noisy. Mine is too quiet to hear more than about a meter away. Maybe buy another one? Or take off the label and add a drop of oil? Or maybe a blade is damaged and rubbing?

Did you try twisting a bit instead of pulling? Grip at the point just before it dissappears with needle nose pliers. Be gentle. Mine both slipped out very easily - the weight of the nozzle was almost enough to pull out.

Yes. Too close. No room for all the plastic to come out so it squirts out suddenly when it can.

Hopefully Daid will answer the question. But FYI... Recently Daid took out most of the features from the print window and now people can create their own "plug in" print windows. There are already a few you can download and try out. I have an ulticontroller so I haven't played with this yet. I'm not sure where you get these plugin guis.

UM2 FEEDER DESIGNS Ian's design is secret for now. Geek's design for UM2 feeder: https://www.youmagine.com/designs/extruder-um2-version-2 Robert's design is here: http://umforum.ultimaker.com/index.php?/topic/4393-ultimaker2-feeder-system-improvements-and-ideas/?p=45758 Post #402. Read Robert's post #409 below that one for more details on assembly and such. Ultimaker's design is in these three posts post #500: http://umforum.ultimaker.com/index.php?/topic/4393-ultimaker2-feeder-system-improvements-and-ideas/?p=50304 Post #279: http://umforum.ultimaker.com/index.php?/topic/4393-ultimaker2-feeder-system-improvements-and-ideas/?p=42330 post #268 http://umforum.ultimaker.com/index.php?/topic/4393-ultimaker2-feeder-system-improvements-and-ideas/?p=42162 I think this second post is more useful. Anyway, contact Bas for a free metal grommet. Takei Naodar's design won't fit on the back of the UM2 so you need to also print his very clever spool holder: https://www.youmagine.com/users/takei-naodar