Print quality problems on curved surfaces and belt tensioning slips on X axis  

Print quality problems on curved surfaces and belt tensioning slips on X axis

Having purchased an i3 MK2 kit a week or two ago, I'm having problems getting consistent prints. Curved surfaces show print artefacts.

I followed the instructions carefully to make sure axes are all in line etc. I've also followed the calibration procedures in the getting started video and in the manual.

Please refer to the album of images i've created at the following link while reading the rest of the post: http://imgur.com/a/otaj9

I have done 4 test prints.

Prints 1-3 were using Slic3r using the "MK2_Slic3r_prusa3d_1_7_3.ini" along with "175mm_Slic3r_prusa3d_1_7_3.ini" from the drivers page on the prusa3d website. Slic3r is from the drivers download also. Firmware is 3.0.7

Print 1 - Initial test print

Print 2 - Printed this after replacing the standard spool holder with one I made myself that has bearings in it. Print improved somewhat.

Print 3 - Tightened the X belt more (Added custom belt clips in ABS to hold belt in place because it slips when tightened). The rest of the print was very good on surfaces parallel to X or Y. Curved surfaces aren't good.

Print 4 - No changes since print 3 but using Cura 15.04.6 with the profile "Original_Prusa_i3_MK2_0_15_PLA_NORMAL.ini" from the prusa3d drivers page. I tried cura thinking maybe the slicer was causing artefacts. This was also after upgrading the firmware to 3.0.8

I have no idea how tight the belts should be. Both the X and Y belts i've tightened by unscrewing 2 of 3 screws of the stepper motor to slacken off the belt, then tighten it by pulling on the belt with the pliers. Then rotate the stepper motor back in to place to tighten it fully. The Y belt is fine but the X belt slips when I tighten it. See the video below:

Prusa i3 MK2 X belt slip when tensioning (note I skip actually pulling the belt with pliers here because it requires two hands but it illustrates how i'm doing it.)

Here are some videos showing how tight the belts are. I don't know if these are too tight, not enough or ok. Maybe someone can tell me?

X tension with head to the right

X tension with head to the left

Y tension, rear

Y tension, front

The filament is genuine Prusa PLA supplied with the printer.

The only other non standard thing is I have the printer on some printed vibration dampeners - see http://www.thingiverse.com/thing:1707045 .

I'm creating GCODE using Slic3r (and Cura for the last print) and printing that via octoprint on a raspberry pi.

So, my questions are:

- How do I get rid of the artefacts on the curved surfaces?
- How come using a spool holder with bearings made such a difference? I see the print farm uses the standard spool holders, from what I can see in the youtube video so surely it shouldn't be affecting things that much otherwise the printed parts wouldn't look such good quality.
- What is the best way to tension the belts and how tight should they be? I've seen people say they should 'ping' but you can get them to ping at relatively low tensions.

TL;DR: Can't get good quality prints. Curved surfaces are particularly bad. Also belt tensioning problems. What is the right amount?