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Lines not touching - UMO

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For already a long time I have some troubles with printing "perfect" surfaces. I have uploaded a few images to illustrate the problem. I tried several things to solve this, but no result. I am a bit lost at this point.




I tried:

- Tightening the short belts (also installed new ones)

- Tightening the long belts

- Lubricating the rods with sewing machine oil

- Trying different settings (wall thicknesses, temperature, infill, speed, top thickness etc.)

However, no improvements. I hope there are some other things I can try to fix this.

Thank you..




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You are underextruding. Assuming there is nothing wrong with your machine there are 2 basic causes:

1) Feeder not tight enough. Try tightening the feeder tension screw quite a bit.

2) Printing too cold or too fast. Try printing at half your current speed to see if that helps. Here are suggested printing speeds/temps.

Here are my recommended top speeds for .2mm layers (twice as fast for .1mm layers) and .4mm nozzle (UM Original, UM2, UM3):

20mm/sec at 200C

30mm/sec at 210C

40mm/sec at 225C

50mm/sec at 240C

The printer can do double these speeds but with huge difficulty and usually with a loss in part quality due to underextrusion. Different colors print best at quite different temperatures and due to imperfect temp sensors, some printers print 10C cool so use these values as an initial starting guideline and if you are still underextruding try raising the temp. But don't go over 240C with PLA.

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thank you for your reply. I tried different speeds and tightened the feeder tension screw. However, the infill of the print still doesn't always touches the perimeter (see image) The print in the image is printed with a temperature of 220 degrees, a speed of 30 mm/s and layer height of 150 microns.


Another thing I noticed is that the fillet on the bottom left is rounder than on the right, whereas the model is supposed to be symmetrical...

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The bottom left corner is a different issue. That's play also known as backlash. On UMO the most common is loose belts. If you push the head to a corner and pluck the long belts they should vibrate at 100 to 200Hz. You can use an oscillator app on your phone to compare pitch. The short belts are easier to tighten - loosen 4 screws to X or Y stepper, push down hard on the stepper (1kg force is good) and re-tighten.

However the underextrusion is the more serious problem. Did you mess with "flow" in cura? There are just so many things that can cause underextrusion. I would start by measuring the pushing strength of your feeder. Put a short piece of filament (maybe 1/2 meter?) into the feeder and only part way into the bowden. Turn the feeder by hand or electrically and see how much weight you can lift. The UMO can lift about 5kg but if your issue is with the feeder than yours is only lifting about 1kg.

If it's the feeder then inspect the knurled wheel carefully. Check the spring, make sure it is tight.

If your feeder can pull > 3kg then concentrate on the hot end. You probably need a new white teflon part or maybe a new nozzle or maybe you can clean out your existing nozzle. Read how to do a "cold pull" but more likely if it's the nozzle it would be just gunk that has burned to a black coating on the inside of the tip of the nozzle.

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The problem has been solved! Apparently the short belts I replaced where not good, so after using the original ones and tightening the feeder tension screw it has been solved.

Now the model is symmetrical and there is no underextrusion left.

Thank you for your help!

Edited by Guest

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