Hopefully have permissions open on this one.
Working to get rid of zits on some tall round prints in Petg. Tries a lot of slic3r settings in 1.3.0-dev to no avail. Tried Cura 2.6.1 still there.
They appear to show up at end of layer.
Only print I have gotren with no zits was in Slic3r 0.9.9 and it took 4 hours. Tries to duplicate those speeds etc to Slic3r 1.3.0 still had zits. Played with retraction, seeing no improvements.
Hatchbox black petg 240 nozzle, 235 nozzle, etc.
I have similar probs. I feel it is something inherit with petg. Its not sticking well on itself in some circumstances like when changing rapidly the direction while layer change. I also had failed prints usding cubic infill were the nozzle crosses old infill the New line does not stick casusing layer shift. So i print honey comb with petg…
PETG will give you the best results when you print nice and slow.
If you’re using Marlin Firmware, i suggest you enable lin_advance which is a pressure control algorithm. It will certainly help.
You may also want to increase your jerk and acceleration settings a little…
The biggest issue i had with zits on my prints was due to jerk and acceleration being too low…
That would explain why the old slic3r 0.9.9 that takes 3.5 to 4 hours prints it near perfectly vs the cura or slic3r 1.3.0-dev which is 2x as fast zits out.
I thought I got all the settings from 0.9.9 into 1.3.0-dev but must be missing something!
it’s been my experience that a perfect first layer is the main factor in preventing petg zits. basically, any at all imperfection in the first layer causes the tiniest amount of material to stick to the nozzle and that’s how it starts. if your bed is perfectly level - try a few different first layer heights, finding a perfect one does wanders.
also, petg likes to be underextruded a bit. e.g: my extrusion multiplier for the current petg i use should be x1.09 (measured by printing a single walled object 0.55mm thick and by extruding 100mm of material) but i use a x1.05 extrusion multiplier and there’s no gaps or underextrusions. it keeps stringing down and i have not had a zit in any of my petg prints over the last year or so.
Tom, I thought a multiplier of over 1 INCREASES flow, and to under extrude you would be .9 or so.
I have been working on dialing in the esteps, but found, due to a sticky on petg on reprap forum when searcing on zits, that extruding 100mm at one whack does not work too well (experienced that with massively inconsistent results). It was recommended that 10 10mm extrusions was more reliable and the best way. My adhoc verified that with give a consistent result that I alightly ever extrude by a couple to 3 mm over 100 with the titan direct extruder.
Planning on looking at the gcode files between the two versions of slic3r to see at the layer changes how much more 1.3.0-dev has put out in total vs 0.9.9.
Finished a print in 0.9.9 that was about 3.5 hours last night and although I can see some zits in the glossy finish, I cannot feel them.
@alan_womack those are really good notes/questions. i’ll do my best to try and explain a bit more.
over/under-extrusion are relative terms. they are relative to a “perfectly calibrated extrusion”. an extrusion multiplier in your slicer of x1 is exactly your e-steps, so if your e-steps are calibrated to over-extrude, even a multiplier of 0.9 may be overextruding, and the same goes the other way around.
i set my e-steps (also using an e3d titan in a direct drive configuration) to exactly the calculated value, and then calibrate my extrusion multiplier for the specific material i’m printing.
e.g - for most petg materials i have to set the extrusion multiplier to somewhere between 1-1.05 for them to underextrude a bit. but, for most pla’s the value for a perfect extrusion would be ~0.97.
the reason for these different behaviors is mainly the geometry of the extruder, without going into too much detail - the filament “bends” around the hobbed gear a bit when extruding. each filament (depending on how flexible/elastic it is and how tight you have the bolt set) bends a little differently and so requires a different amount of steps to extrude the same length. so for different filaments and filament types you will have different extrusion multipliers for a “perfect extrusion”.
i always use 2 tests when calibrating. both a single walled object with the perimeter width set to 0.55mm (fine tuning), and an extrusion of 80-100mm measured (rough tuning). for a titan extruder, set up properly you should not have any significant difference between extruding 100mm or 10x10mm (if you are doing the extrusion at a reasonable speed). as a matter of fact - if anybody is not getting consistent results when extruding 100mm (i have first layers that are much more than that) i would suggest they either switch extruder or improve their configuration. extrusion should be relatively consistent and repeatable, and if that is not the case - there’s usually an underlying problem in my experience.
to put my money where my mouth is - i just extruded 100mm of the fluorescent pink (supposed to be red) chinese petg i now use x5 times using only the e-steps and got ~92mm each time.
also - i would recommend giving prusa’s version of slic3r a go https://github.com/prusa3d/Slic3r/releases
after using the original slic3r for a few years, it’s a marked improvement over the original (with 1.36.0 just released).
Thank you will do that and print one. If you are extruding 92 and then have your multiplier in the slic3r then you are extruding even less when printing?
Assuming you extrude in from pronterface.
Md Mainuddin
re-read my comment, as i mentioned - i should be using a ~x1.09 multiplier in slic3r (92x1.09=~100) but instead i use x1.05 because petg should be underextruded a bit.
just to emphasize - 2 factors are important:
I went back into the gcode and although they may be doing two different infills between that much version, there was nearly 3mm more filament in the zit fested slice vs the smooth one.
When back to the printer, will make a .1 change to extruder to extrude less (.9) in my case and see what that looks like for zits.
