Confusion About Print Speed and Max Volumetric Speed (MVS) in Default Profiles

[atestani]

I’ve been happily using my Q1 Pro, but I’ve run into a confusing aspect that I hope can be clarified. The issue revolves around the relationship between print speed and Max Volumetric Speed (MVS) in the default profiles.
For example:

• The Generic PLA profile has an MVS of 14 mm³/s at a print speed of 150 mm/s.
• The Rapido PLA (HS) profile has an MVS of 24.5 mm³/s at the same print speed of 150 mm/s.

Assuming the formula for MVS is: MVS = Layer Height * Extrusion Width * Print Speed, the actual print speed will be limited by the MVS in some cases, but the user isn’t informed of this limitation.

For instance, with a 0.6 mm nozzle, 0.24 mm layer height, and 0.62 mm extrusion width:
With MVS = 14 mm³/s, the actual speed is limited to ~94 mm/s (which is below the 150mm/s set speed so the print is limited to 94mm/s).
With MVS = 24.5 mm³/s, the actual speed could reach ~164 mm/s (which is above the set speed of 150 mm/s so the print runs at 150mm/s).

This inconsistency raises multiple questions:

• Is the MVS calculation in QidiStudio and QidiSlicer profiles based on the formula MVS = Layer Height * Extrusion Width * Print Speed?
• Why are there both print speed and MVS settings? If MVS limits the print speed, why not have just one setting?
• Why do some default profiles have the same print speed but different MVS values? For example, why does Generic PLA have an MVS of 14 mm³/s while Rapido PLA (HS) has 24.5 mm³/s, both at 150 mm/s?
• Why isn’t there a warning when the print speed is limited by the MVS? It would be helpful to know if the preset speed cannot be achieved due to MVS constraints.

I’d greatly appreciate any insights or explanations anyone provide.

Thanks
Al

[Bikeracer2020]

This might help..... https://3dprintbeginner.com/bambu-st...ps-and-tricks/

[atestani]

This might help..... https://3dprintbeginner.com/bambu-st...ps-and-tricks/

Thanks for that. It does help but it shows there is a lot more complexity and more questions here. There is also a link in the article to another article on Flow rate which comes into this as well. In QidiStudio, there are calibration procedures for MVS (Max Volumetric Speed), Flow Rate, and Pressure Advance. I am still trying to understand all of this but get the sinking feeling is that to optimize performance with print quality you need to do calibration for each filament and speeds and feed you are trying to use. Then from there you inspect the test model and adjust your parameters.

This all started because I bought some eSun PETG+HS which is supposed to print 3X faster than their standard PETG. When I got to looking at how to actually take advantage of the increase in speed in a preset I was creating for this filament, I found that MVS that was basically limiting whatever value I put in for speed(s). MVS was even limiting the Generic PETG speed.