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Serious underextrusion

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The fan seems to be working fine.

I have to pull quite hard to get the filament out at 90 degrees, is that normal?

Update: cleaned the nozel, started cylinder rest again, the 3mm part is perfect but as soon as it got to the next part it started underextruding

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Have a look at the nozzle temperature during printing. It should not vary more than +/- 1 degree celsius/Kelvin.

Also check if the filament roll is rotating easily means there is little tension on the filament before going into the feeder. Thats something i am actually monitoring, after getting rid of the temp variation.

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Large temperature errors could have several causes, with different fixes for each. There's no point in going into them until you verify that you have a problem, which IMHO is unlikely. And the +/- 1C thing should be taken with a large pinch of salt, what you're looking for is that the temperature is not wildly off. Temperature fluctuations can cause poor surface finish, but I don't see how it can cause underextrusion unless it not hot enough to melt the plastic.

On the filament being quite hard to pull out when cleaning the nozzle. Without being there to judge what "hard" means, I would say that if true it could mean that the teflon spacer is deformed. Otherwise, a general difficulty removing the filament - if the Bowden is still in place - could mean that the Bowden is not pushed all the way in. That leaves a gap between Bowden and spacer in which a collar of plastic can form, making the filament hard to remove.


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Hi There.

So - here is a great example of what some careful maintenance can achieve.

Witness the photo below which shows a 'before' and 'after' maintenance on the SAME printer, about 30 minutes apart.


Here is the story:

- I have had this Ultimaker 2 since November 2013. It was not until May 2014 that I started evaluating its performance - since until then I was quite happy with 0.1mm layers at 50mm/sec speed - and most Ultimakers can do that *fairly* well - even sick ones.

Anyway - as soon as I first did the 10mm3 test - I could see I had a problem. To cut a long story short (long story is at http://umforum.ultimaker.com/index.php?/topic/4586-can-your-um2-printer-achieve-10mm3s-test-it-here/) I fixed this problem once before, with *alot* of work and research.

The good news is that that knowledge is now pretty well known, so today when I blew the dust off my UM2 after several months, I was prepared.

Over the summer I really hammered the UM2, printing a batch of 200 prints of the same thing, each took about an hour. As the batch progressed, the quality deteriorated a little, so it was clear something was 'wearing out'. At the end of the batch I shut down my little factory and got on with something else.

Today I came back to the UM2, just as I had left it (in my garage), and the first thing I did was run a 10mm3 test. That is the green one on the left of the picture. As you can see - its a total fail.

Fortunately, I knew what to do - and here it is:

1) My printer has been stored in a (cold) garage (in the UK). Its not really damp as such, but its what you might expect. I had left the filament loaded and on the spool on the back. So, we can probably expect the filament to be a little damp.

2) I brought everything inside for a bit of TLC.

3) First task, take the old filament out. As it happens, I ended up with the filament getting jammed in the bowden tube on the way out - due to an oversized blob at the nozzle end. I removed the 2 bowden clips and got the tube out, with the filament still stuck inside. After a bit of work with pliers I got the filament out. Now - important - I took this opportunity to lubricate the bowden a little - I got a length of filament and sprayed it with silicon lubricant spray - then worked it back and forth inside the bowden tube for a while. You will feel the (noticeable) difference this make.

4) Next, I did the hot-in-cool-out process, (some people call it 'atomic' I believe). Basically, with the bowden removed and filament manually fed into the top of the heater block assembly, heat up the head to 190 degrees (or a little hotter) and push the filament through until you get plenty coming out. Now let the nozzle cool to 90 degrees, and as soon as it does, pull the filament up and out on one quick jolt. You will get a nice little rocket shaped tip to the filament. If you study this tip you can learn alot about the state of your head. For example, if its covered in old filament, you may want to repeat the process a time or 2 more, to clean out all that old stuff. Also, look at the *shape* of the rocket - this is a cast of the inside of your head block. A perfect cast would have the 3mm filament join seamlessly to a 3mm diameter rocket with perfect smooth sides and a smooth taper to the 0.4mm tip. What you might see instead is buldges, particularly at the junction of the filament and where the rocket starts (there are photos of this in the 'long' thread linked above). The buldges may indicate problems with the assembly, or the teflon coupler. You might have a stretch between the 2 pieces if you pulled hard, so ignore that.

5) In my case I was pretty certain the teflon coupler was worn out, from previous experience, so I disassembled the head block and took out the white teflon coupler. As I expected, looking inside the hot end of the coupler there was buckling inside with a small cavity in the walls before the filament exits the coupler. I believe that the filament gets jammed on this, both when loading filament (thats a good sign of this problem) and also whenever snags in the filament go through (particularly when the feed motor has chewed the filament a little). I had a spare Teflon piece in stock so I quickly replaced it.

6) Having meticulously reseated the bowden tube (make sure there is no gap between Bowden, teflon and nozzle sections of the filament path), I put on some nice, new, dry Faberdashery PLA, from loose wrap of material.

7) See the after picture. This was literally the next print. You can see that the results go from zero to 10mm3.

If i had time, I would have also dismantled the feeder mechanism and cleaned out all the little PLA chips which build up in there.


- Get a spare Teflon Coupler or 2. I believe this is the #1 fix for under extrusion.

- Lubricate the Bowden tube

- Clean out the nozzle with the hot in- warm out method

- Use dry Filament, on a loose spool.

I will also run a little sewing machine oil into the rails, since this UM2 had such a hard run, and probably grease the Z axis. However these things wont really help extrusion, but may keep it running quiet and accurate.

Finally - I believe Ultimaker have now created a glass-impregnated Teflon coupler, (Mine are all the original type) and I suspect the glass might help keep them going longer, since overheating and general heat-fatigue seems to be what makes them deform.

I hope this helps.



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A very good review, thanks for that :-)

The new glass filled PTFE ColdEnd's have a much rougher surface, and in interaction with normal PLA these may be even faster than the previous ones wear out. Anyway, I have two of them, each used less than 2 weeks, and there are first visible signs of wear.

With relatively small optimizations and without additional lubricant in the Bowden, I can achieve interesting improvements:




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i know it's been a while, but i finally got around to ordering spare parts dissasembling my printer.

i just got a question, the trouble with the teflon part is deformation which causes friction on the filament, but now i took out that part, i can slide it over filament without any friction. is that normal for deformed parts or does this mean the teflon part wasn't responsible for my prblems?


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That's puzzling. You seemed to be saying above that the filament wa quite hard to pull out when you were cleaning the nozzle - presumably with the bowden tube removed. With the tube removed there's essentially nothing between you and the nozzle except the PTFE spacer, so it should feel about the same whether inside or outside the printer.

Is there deformation of the mating face of the spacer? If there was a gap then melted plastic could get into that gap and make the filament hard to withdraw. That wouldn't be obvious with the spacer held in your hand.


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