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UM2: Hard to get good prints


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Posted · UM2: Hard to get good prints



I have big troubles with getting nice looking prints on my UM2.


The unit is quite old, but I have replaced these parts this summer:

* New heat element for hot end

* New 0.4/0.6mm nozzles (Olsson Block)

* New PTFE coupler

* New knurled wheel on extruder


What is broken and needs to be fixed:

* Temp sensor on bed (currently printing without heated bed)


Look at this print (Cura 5). Regular white PLA (a couple of years old). Both printed at 0.2 layer height and 60mm/s. Left one 210C and right one 220C.


By now, I don't really know what to try more to get better results. It feels like I have replaced every part that can cause issues, but still here I am 😄 


Any ideas? 🙂


/ Oskar



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    • 2 weeks later...
    Posted · UM2: Hard to get good prints

    I have the feeling that you printed this a bit too hot and too fast. Also, white often does not print too well, I am not sure why but I guess because it has fillers to make it opaque white. Further, older filament might be moist, or it might have become too brittle or too hard to feed well. If the spool is nearly empty, a hard and tightly wound filament will cause a lot of "unwinding resistance" (=it acts like a spring and wants to wind-up again) and cause a lot of friction in the bowden-tube and nozzle, causing under-extrusion. This is a known issue with the UM2. If so, you could unwind a bit manually, bend it in the opposite direction around a skater wheel, release again: this will straighten it somewhat, causing far less friction and resistance.


    For best quality, print slow, in thin layers, and cool (=at the bottom of the temp-range of the material), with new filament, at the beginning of the spool (or if at the tight-wound end, after straightening the filament). For example, printing 0.06mm layers, 25mm/s, 190°C for PLA, will give good quality, but will cost an endless amount of time, 12x longer than printing at 0.3mm and 50mm/s...


    Most of the time I print PLA  at 210°C, 35-50mm/s, and 0.1-0.3mm layers, with decent quality, good enough for the purposes.


    If you are relatively new to 3D-printing, or on an unknown printer, make a small test model, and print that with different settings. Or change the settings on the fly while printing (temp and speed), to see the effect.




    Testprints at various speeds and layer-heights: from left to right: 0.4, 0.3, 0.2, 0.1, and 0.06mm layers; top row at 50mm/s, bottom-row at 10mm/s. Material is PET, transparent to see what happens inside. The watermark is halfway inside the model. Test-block dimensions are in mm: 20 x 10 x 10, hollow watermark text is 3.5mm caps height and 0.5mm leg width.





    High-quality print with 0.06mm layers and ca 0.35mm/s (if I remember well). Ruler is in mm and cm.



    Standard quality print at 50mm/s.



    Unwinding and straightening a bit of old, stiff and too tightly wound filament, by bending it around a skater wheel in the opposite direction, then releasing it again. After that, its bending radius is about 30cm, the same as that of the bowden tube, thus causing almost no more friction and no more unwinding resistance in the feeding system.



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