Combing Option causes issues

[davidmo 0]

Combing on different settings causes different issues. I researched and found suggestions to the issues but in the end it turned out to be combing, I wanted to preface that by saying I've done various calibrations, confirmed my prints are accurate when measured and my flow rate is correct. I've tried several different retraction settings as well because I saw others with a similar issues and the common suggestion was retraction.

 

I have a Prusa i3 MK2 build with nearly all the same parts except a RAMPS 1.4 board. 

Since I mentioned retraction its at 2mm 40mm speed. Print speed is 45mm.

 

When I toggle combing all I get lots of surface artifacts and very poor print quality

When I toggle infill only I get some areas that fail to extrude near the start of the extrusion on a layer

If I toggle avoid printed parts there doesn't seem to be much of a difference

If I toggle the setting off the prints look great however I have some larger prints which require a high percentage of infill and as you know this process would raise exponentially in time

 

I tried to take the best pictures i could, the prints dont look the greatest due to camera flash however the quality is quite good, less the issues. The anomalies appear during the same layers on each print.

 

Note on infill only When the X starts then about half up the X and again near the top, all on the left side of cube, this also happens on other sides but in different locations, within the slicer it appears these are layer starts. I have also played with my Acceleration and JD settings to see if that makes a difference and it does not. I have reasonable settings (900 Acc x .0444 JD) Have tried 400-700 Acceleration as well with other JD variables calculated based on a Jerk value of 8-10.

 

[davidmo 0]

I decided to run another test with Combing Infill only and turn on Retract before outer wall hoping this little retract would be enough to get the filament back where it should be. The only thing I could imagine thats happening when the issue occurs is that the combing pulls a little too much filament out of the nozzle (this is PETG so it might be a little more stringy and stretchy compared to PLA) and then that little bit is missing at the start. If I was over extruding I may not even notice it.

 

Anyway TL:DR is that with Infill only and Retract before Outer Wall turned on the issue seems to have gone away.

However I wouldn't exactly consider this a closed case as it shouldn't happen with some internal slicer tweaking. Maybe an option can be added similar to the option "Retraction Extra Prime Amount". But instead it would be "Combing Extra Prime Amount" and what this setting would do is allow an extra little prime after combing on exterior walls.

[gr5 2,268]

I think you want the feature "max comb distance with no retract".  I've had to use that when printing > 200mm/sec.  Otherwise it leaks too much during the combing step.

[davidmo 0]

I thought about that however when using 70-90% infill this is a moot setting as many of the infill runs are well below any reasonable setting and I cant predict which infill move will be the last before moving to the wall.

Since Combing is only set to infill (for my example) I have to assume the setting is in relation to infill and not the distance of the next move (i.e. the wall) and is the distance of the previous move (i.e. the infill).

 

[burtoogle 516]

I have found that because PETG is so runny, combing is not appropriate for a lot of models. If you do use combing with PETG, use a very small max comb distance with no retract. Certainly no more than 10.

 

The combing mode (all, not in skin, within infill) does not influence which travel moves will use combing, only the routing, i.e. not in skin will route along walls and over infill but (when possible) not over skin areas. You would be forgiven for thinking that within infill mode would route only within infill but, in fact, it will also route across areas of skin which is why I created the not in skin mode to stop combing trashing skin.

[davidmo 0]

I wasn't referring to the routing but which distance is used to calculate the max comb. I assumed it was the current / previous line and not the next line so with a setting of Infill Only this would mean the current then previous infill line and not the wall line. 

 

I did also have much of the same experience with PLA+ from eSun, especially the horrible surface quality when using the All setting. It looks like I turned on the fuzzy print setting or something, like a weird textured / grain pattern. 

[burtoogle 516]

The distance used in the max comb distance with no retract feature is the combed distance from the point where the travel starts to the point where the travel ends, what happens before and after those points (infill, walls, skin, etc.) is not a consideration.