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Underextrusion Problems

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I have had this UM1 for a year and things have gone well. Lately however I have been having problems with sporadic under extrusion. I was compensating by printing hotter and hotter, but once it got to 255 I finally ordered some replacement parts and started trying to get under control. Between my fully functional UM1 at home's parts and replacement parts I have replaced the Nozzle, the brass insert, the brown peak tube, the thermocouple, the wooden feeder gear and knurled bolt thing inside.

I am using brand new silver filament from Ultimaker. I have measured it with calipers to be 2.85mm. I print at the Cura default speed of 50 mm/s and a layer height of .2. I have examined the roller wheel on the feeder and I don't see any dents or damage to it. The filament in the bowden tube does show signs of stripping when the under extrusion happens

I have been printing at a temp of 220c for as long as I can remember, on this printer and the one at home. The one at home still works just fine at 220.

Right now it seems like 230 is the magic number on this one. Anything less and I get sporadic spots in the print where their will be dotted lines where filament didnt properly extrude. 230 isnt terribly hot but it doesnt cause subtle drooping in some prints and I worry that if I let it go I will be back up to 255-260 before I know it.

Any ideas as to what is going on? How can I get this thing working smoothly at 220 again?



Mid print snapshots while printing at 220c:



The cube on the left was printed at 230 while the one on the right at 220.




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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:



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1.) You appear to be on to something here, though, I am not sure if its the whole thing. When I did a test print with the fan turned off the under extrusion seems to be reduced. Still present, but reduced. It occurs to me that a difference between the working UM1 at home and this one is that I printed new fan shroud for that one. Is there one you would recommend specifically?

2.) I just replaced the thermocouple so it seems unlikely. If it is the thermocouple it is at the very least consistent. I have watched the temp reading during the print and it never varies more than a degree (Except when the fan kicks on but that is quickly recovered).

How can I tell if it is boiling? Just heat it up and listen and watch for bubbles in the filament as it oozes out of the nozzle?

3.) I have never printed ABS, and as I mentioned the nozzle, brass insert and peak tube are all brand new from UM, so clogging in there from gunk seems unlikely.

4.) I will have to gather some equipment to perform the test you suggested, but I will say that in the past when cleaning the nozzle I haven't ever found any wood debris.


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If there is wood debris you can usually see it by removing filament and looking into the feeder with a flashlight - you don't have to take anything apart.

Test boiling by touching a drop of water to the aluminum block. Use finger or qtip ear swab.

Also room temp should read about 20C when the machine has been off for 30 minutes.


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