Using Max Volumetric Speed with PrusaSlicer¶
These notes are based on my experiences with the Prusa i3 Mk3 printer. If you are using a different printer, please verify the hardware details are same. These pages may be a bit rough as I revise them and add new material. Please check back regularly for updates.
PrusaSlicer is one of the few slicers to support a maximum flow rate for the hotend, and this setting is your best friend when printing with multiple nozzle sizes. The amount of filament that a hotend can process is specified in cubic millimeters per-second (mm3/s). PrusaSlicer allows you to specify this value with the
Maximum volumetric speed (MVS) setting in filament and print settings profiles.
Calculating maximum volumetric rates is straightforward:
Max. Volumetric Rate = Layer Height X Extrusion Width X Speed
The reason that this setting is so powerful is that it allows you to specify a single setting per filament and PrusaSlicer will ensure that print speeds are throttled to stay below your specified volumetric rate. PrusaSlicer also supports setting MVS in print settings profiles as a master limit. I can set my preferred speeds for each feature and the volumetric limits will throttle when – and only if – necessary to keep the flow of filament within the hotend limits. This allows me to use a single print settings profile across all nozzles and filament types. I just need to set an appropriate MVS value for each filament.
Life is a lot more difficult if you’re using another slicer that doesn’t support volumetric limits. You have to set your max speeds to ensure you never exceed the hotend capacity, which means you have to determine the worst case for flow rates and reduce speeds accordingly.
The max volumetric speed you should use depends on your hotend. The E3D V6 hotend that ships with the Prusa i3 Mk3 is advertised with a rate of 15 mm3/s, though in practice 11.5 mm3/s is realistic. If you need to push more filament, the Volcano hotend upgrade increases this to roughly 25 mm3/s but does require some printer and software modifications. Other hotend designs allow even higher flow rates.
Individual filaments also have different characteristics. Viscocity, content and other factors may greatly reduce effective throughput. Most PETG, for example prints well at a recommend rate of 8 mm3/s as compared to PLA at 8-15 mm3/s.
Much of the time, neither linear speeds nor volumetric throughput matter when doing small prints. The nozzle never comes up to full speed and spends most of the time speeding up and slowing back down at lower speeds. It’s when you start doing larger parts or moving fast for things like infill that it matters. “Obeying the speed limit” with the volumetric setting avoids extruder clicks and jams that can spell disaster mid-way through a large print.
Adjusting filament profile max volumetric speed¶
MVS can be set on a per-filament basis under
Filament Settings. This allows each filament selection to control overall print speeds.
Adjusting print profile max volumetric speed¶
MVS can also be set under
Print Settings I like to set a maximum “master” value of 11.5 mm3/s here as a safeguard.
Viewing the effects of settings changes¶
Slice, save, then look around in preview to see the impacts on speed and volumetric flow:
Contact and feedback
Thanks to @hwlin on the Prusa forums for the suggestions on clarifying this page.
Last updated 20191125