Print defects on curves (s-curves)

[angryfatcat 1]

I'm relatively new to Cura and I'm running into a problem that looks like its related to slicing and not printing.  I've tried about a dozen times to print this object with out the defects that appear around the curves areas on the front and back (where it curves in, out and in again).  After making no improvements, I re-sliced this with PrusaSlicer using the same basic settings and the defects were gone.  There is an exposed z-seam on the side, which is not in view.

 

 

I'm a big fan of Cura, so I'd really love to know how ot print this successfully without having to use a different slicer.

 

Printed on an Ender 5 Pro with AMZ3D Dark Violet PLA

Nozzle: .4mm

Layer Height: .2mm

Wall line count/thickness: 4/1.2mm (have gone down to 2 - no improvement)

Infill:40% (have gone down to 0% with no improvement)

Printing Temp: 205C (Also printed at 185C, no improvement)

Build Plate Temp: 65C

Print Speed: 80 mm/s (60 mm/s  and 50 mm/s look about the same)

Wall Speed: 40 mm/s (also tried 30, 25)

Retraction: 5mm at 25mm/s

Fan Speed 100% after layer 4

Coasting enabled

Sliced with Cura 4.6.1, printed via SD card, Bed leveled with BLTouch.

Firmware is Marlin 1.1X .

 

I've tried:

• Slower speed

• turning off coasting

• fewer walls/no infill

• Equalizing nozzle pressure

• Reducing flow rate for the outer wall down to .95

• Turning off/adjusting retraction speeds

 

I'd really love to figure out how to print this without those defects from Cura.  Any help or suggestions would be greatly appreciated.

[gr5 2,071]

Try checking "outer before inner" and set ALL printing speeds to 35mm/sec (no speed changes allowed).  Travel speed should be fast - 150 to 300mm/sec

[angryfatcat 1]

19 hours ago, gr5 said:

Try checking "outer before inner" and set ALL printing speeds to 35mm/sec (no speed changes allowed).  Travel speed should be fast - 150 to 300mm/sec

 

Setting it to 35 mm/s didn't do it, but bringing everything down to 15mm/s did.   Other than the z-seam, its just about perfect.

 

I still wonder if this could be handled at a more normal print speed with jerk and acceleration control - which were not enabled.

 

[gr5 2,071]

Usually high jerk and high acceleration reduce blemishes.  Everytime the extruder slows down or speeds up you get over or under extrusion.

 

However 15mm/sec is crazy slow.  Well below jerk setting such that the extruder should not be speeding up or slowing down at all.

 

So I'm not sure what is causing your blemishes.

 

Did you try the "outer before inner" setting?

[angryfatcat 1]

Both the 35 mm/s and the 15mm/s used outer before inner.

 

Maybe my thinking is wrong here but if at 15 mm/s works but normal speeds do not - then it must be some form of overshoot.  Essentially, I've taken Jerk/acceleration out of the equation at these speeds.

 

If Prusa can print this at speed - then I would think Cura could as well.  I'm looking at some of the differences in the gcode:

 

Prusa:

M201 X9000 Y9000 Z500 E10000 ; sets maximum accelerations, mm/sec^2
M203 X500 Y500 Z12 E120 ; sets maximum feedrates, mm/sec
M204 P1500 R1500 T1500 ; sets acceleration (P, T) and retract acceleration (R), mm/sec^2
M205 X10.00 Y10.00 Z0.20 E2.50 ; sets the jerk limits, mm/sec
M205 S0 T0 ; sets the minimum extruding and travel feed rate, mm/sec

 

Cura:

M201 X500.00 Y500.00 Z100.00 E5000.00 ;Setup machine max acceleration
M203 X500.00 Y500.00 Z10.00 E50.00 ;Setup machine max feedrate
M204 P500.00 R1000.00 T500.00 ;Setup Print/Retract/Travel acceleration
M205 X8.00 Y8.00 Z0.40 E5.00 ;Setup Jerk

 

So it looks like the X/Y jerk is higher in Prusa, but the Z/E jerks are higher in Cura.

The accelerations are also much higher in Prusa than in Cura.

 

I guess my question is - am I on the wrong trail here in thinking that the jerk/acceleration could be the cause?

 

[gr5 2,071]

Absolutely, but more likely low jerk/accel could be the cause.

 

If you have overshoot or ringing (I see neither in your print) then you need to tighten the belts.  What I see doesn't look like those - what I see in the photo looks like overextrusion briefly.  This can be caused due to speed changes or other strange movements like coasting and others.

 

Overextrusion is usually worse with low jerk/accel because the printer slows down for longer and that high pressure in the nozzle causes it to squirt out and make a bump.  With high jerk/accel the printer either doesn't slow down at all or it slows down so briefly it's not enough to cause pressure buildup in the nozzle.

 

I'd look very carefully at the gcodes happening right when these bumps happen.  Maybe use the free "repetier" software that lets you see gcode and 3d view of the gcodes at the same time.  You can highlight a gcode or a group of them on the right window and see where in your model they happen in the left window.

[angryfatcat 1]

On 6/12/2020 at 9:54 AM, gr5 said:

Absolutely, but more likely low jerk/accel could be the cause.

 

If you have overshoot or ringing (I see neither in your print) then you need to tighten the belts.  What I see doesn't look like those - what I see in the photo looks like overextrusion briefly.  This can be caused due to speed changes or other strange movements like coasting and others.

 

I tweaked both the Jerk and outer wall acceleration upwards (7 to 10 for the jerk, 500 to 650 for the acceleration) and this seems have fixed the problem without introducing any ringing.  So, I think your suggestion was spot on.