Slic3r Volumetric Speed

  • After using Simplify3D for a while I decided to try the Prusa version of Slic3r. Overall I am happy with the results and being able to use firmware retraction without any editing and volumetric extrusion. I am trying to fine tune my setup. It is a Wanhoa duplicator 6 converted to duet wifi and an E3D chimera dual nozzles 0.4mm and 500mm capricorn bowden tube. Using pressure advance never seems to change anything so I have been running with it disabled. My retractions are 3.5mm at 75mm/s for ESUN PETG. I would like to try the Max Volumetric speed in slic3r to adjust the speeds for constant pressure but I do not know what the values are derived from and havent found much on google. I saw somewhere that If i am printing at .5mm width, .15mm layer height at 40mm/s print speed (.5x.15x40) that my volumetric speed should be 3mm3/s but it prints very slow. That formula doesnt seem right since that is not the volume coming out of a .5mm layer width. Anyone have any advice on what a proper value would be or the way to determine this value? I know that I can extrude 5mm/s at 240C without my titan extruder skipping.

    Thanks for any tips! Nick.

  • Moderator

    3mm3/s isn't your max volumetric speed though. That's just what you'd be pushing at those settings. The max for your hotend is probably closer to 10-12mm3/s.

    I tried volumetric speed control with Slic3r for a while but could never get good quality print results. It would either print insanely slowly or insanely fast. It took a bit longer, but I eventually just tuned the individual speeds for different movements until quality was good and then just lived with the speed.

    The goal of volumetric extrusion is to make gcode more portable between printers, along with firmware retraction, etc. A laudable goal, but not one I really see becoming successful. Though I know DC42 has set his sights on making it more practical in general, so show me wrong David. 😉

  • I think there are two different things here, 'volumetric E(xtrusion)' under Printer Settings -> General -> 'Use volumetric E' and 'Max volumetric/print speed' under Print Settings -> Speed -> 'Autospeed (advanced)'. I don't use volumetric E, but I do use Autospeed.

    The max volumetric speed setting is a function of (at least :-))) your nozzle, hot end, filament and extruder. You determine the limit by doing a series of extrusions at different speeds and temperatures and testing by either/both listening for the extruder skipping steps or grinding, and measuring to see if you actually pushed the exact amount of filament through the system as intended (mark e.g. 50mm on the filament passing a fixed point on your printer before the extruder). See step #9 of (not very clearly written if you try to follow the steps through, but the math is useful).

    First thing I do when I get a new roll of filament is 'calibrate' it in this way and add the info to a spreadsheet - preferred temperature and max volumetric speed. Some side comments: (1) this makes filament samples a bit more useful as you can actually see how the sample compares to your other filaments, and (2) this causes me some frustration that David doesn't enable more filament monitor information when simply extruding into air, but that's all a work in progress and I can see there's some back pressure to consider as well in the calibration results.

    The benefit of doing this (for me) is that I skip optimising the 10 speed parameters and just set 'Max print speed' and 'Max volumetric speed' as overrides so they show in the Plater tab. Presumably the max print speed is a function of printer structure, belts, etc.? I know that the calibrated filament result is a 'hard' limit - go past this and the system -will- under-extrude, and otherwise I have one or two knobs to adjust speed vs. quality and leave it at that.

    I've not used the Prusa Edition of Slic3r btw, I am very happy with the '1.3.0-dev (automated fresh builds)'.

  • When using the auto max speed, are custom still speeds taken into account? For example, bridges speed…

  • Just to follow up, i did get my slic3r dialed in using a volumetric max speed of 8 mm^3/s and 60mm/s max auto speed. I tried letting slic3r do all speeds automatically except the first layer and small perimeters. Print speed wasnt too bad, every now and then a single layer would print very slow while the rest appeared to be closer to the max of 60mm/s. I was not trying to really print faster, just make sure that the filament flow was consistent. I ended up going back to Simplify3D. While i wish they did more updates and had some newer features like setting up more speeds for different features and native firmware features, the prints came out better even with similar settings. I also ran out of PETG and picked up another roll. I was using eSUN white but the local fry's electronics store didnt have anymore so i got some MG chemicals PETG natural… they have a pretty poor filament selection. The MG chemicals PETG prints much different than the eSUN and actually is drastically better in terms of quality and strength. FYI for those interested.

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