Bulging / round corners
Hello,
I have been enjoying my MK2S and have put several KG of filament through it without any serious issues, except one thing that I cannot seem to figure out. That is, on any print with a sharp-ish corner (say <135 degrees or so), I get a bulge at the corner as pictured below. The only solution seems to be to significantly reduce the outline speed. I have seem many people printing at higher speeds without this issue, so I must have some mechanical or software issue.
My prints are dimensionally accurate with an extrusion multiplier of 0.98 and I seem to have this issue when printing from S3D or Cura (only slicers I've used). My belts are quite tight (Audible twang when plucked) and I do not experience any other print issues.
A speed of 24 mm/s perimeter yields acceptable results and it gets worse as I go faster. Looking at the print under a low power USB microscope, it appears that I over-extrude at the corners, but not elsewhere. Lowering the extrusion multiplier seems to reduce print quality all over and only slightly helps with this issue.
Any ideas?
Re: Bulging / round corners
That's simply because at higher speeds, you are building up more pressure in the nozzle and when the extruder stops at the corner, the pressure is released.
At lower speeds, the pressure in the nozzle is a lot less.
Peter
Please note: I do not have any affiliation with Prusa Research. Any advices given are offered in good faith. It is your responsibility to ensure that by following my advice you do not suffer or cause injury, damage…
Re: Bulging / round corners
The speed will also have an impact on corners in it self. Think about the belts - they will probably act as a springs and jerk the x-axis as well as the y-axis as a pendulum when moved fast.
/Henrik
Re: Bulging / round corners
That's simply because at higher speeds, you are building up more pressure in the nozzle and when the extruder stops at the corner, the pressure is released.
At lower speeds, the pressure in the nozzle is a lot less.
Peter
This is exactly what I suspect is happening and increasing acceleration does slightly improve the issue. Is there any setting or adjustment that can be made to have the extruder slow down during corners?
The speed will also have an impact on corners in it self. Think about the belts - they will probably act as a springs and jerk the x-axis as well as the y-axis as a pendulum when moved fast.
/Henrik
This is definitely true as well and is pretty hard to avoid without going to a ballscrew machine. I don't think the speeds I'm working at should have that much of an impact in this way, though I haven't weighed the carriage and done the math.
Re: Bulging / round corners
I think that reducing the acceleration value (quite significantly) should work, but the best thing to do is to print at a speed where you don't have the problem.
If you want accuracy with this printer, you have to print perimeters first and keep the print speed slow. Actually, try printing perimeters first, set perimeter speed to 20 (or 30) mm/s; leave the loop and infill speeds the same.
Peter
Please note: I do not have any affiliation with Prusa Research. Any advices given are offered in good faith. It is your responsibility to ensure that by following my advice you do not suffer or cause injury, damage…
Re: Bulging / round corners
Linear advance was merged into the firmware. that will help. it's not in the latest release but the main branch so you would have to re-flash.
See:
https://github.com/prusa3d/Prusa-Firmware/issues/75
http://marlinfw.org/docs/features/lin_advance.html
Re: Bulging / round corners
Now if they would just add pressure/linear advance to the firmware, it would be good (i think marlin has it already)). i've been experimenting on my larger cartesian and one thing other than corners is holes. they look much better, like holes without that extra bulge on their side. However it's a different setting for different filaments and even temperature so it's yet another value to dial in.
But If you go too slow on perimeters you can also start seeing stepper motor artifacts since microstepping and drivers aren't great at smooth motion at lower speeds. you can get those tiny vertical lines (not ringing....) across flat surfaces, going faster reduces or eliminates them. Slightly better with geared extruder since it has to go faster for the same extrusion rate but mk2 is direct.
Edit: looks like the PR was actually merged in the firmware. Yay.
Re: Bulging / round corners
Linear advance was merged into the firmware. that will help. it's not in the latest release but the main branch so you would have to re-flash.
See:
https://github.com/prusa3d/Prusa-Firmware/issues/75
http://marlinfw.org/docs/features/lin_advance.html
Not sure it is in the current PR firmware, but in this branch: https://github.com/Sebastianv650/Prusa-Firmware/tree/MK2-LIN_ADV-PR
Peter
Please note: I do not have any affiliation with Prusa Research. Any advices given are offered in good faith. It is your responsibility to ensure that by following my advice you do not suffer or cause injury, damage…