# Extusion rate limiting and firmware retract

One frustration I have with Cura is that it has no way to set print speed in terms of a volumetric extrusion rate, when extrusion rate is the main physical limiting factor for how fast you can print. It's a pain having to have different speed profiles for different layer heights (and doesn't work with adaptive layers!), different line widths, different materials, etc. I'd like to just set a feedrate limit on the extruder axis, which would achieve this and make it easy to switch already-sliced models between different materials. However, having a low extruder feedrate limit would make retraction and recovery from retraction incredibly slow, to the point of being unusable - since I've found quality so much better without combing, I now have a lot of retractions.

I'm thinking about building Marlin with support for firmware retraction in hopes that the firmware-retract command can ignore the configured extruder feedrate limit to still do rapid retract/restore, but I don't want to waste a lot of time on it if that doesn't work. Can anyone with experience with this feature confirm whether it ignores the normal extruder feedrate limit? Or, if you have experience with a similar configuration, can you share results on how well it worked?

Sadly this does not work at present. Setting an M203 E3 resulted in 6 mm retractions via G10 taking 2 seconds each vs the fraction of a second they're supposed to take.
In principle, G10 firmware retractions still make it easier to script a soluton (replacing each G10 or G11 by a sequence of M203, G10/G11, M203 to set E-axis speed then reset it around the operation) but this is less friendly to direct usage of same sliced files with different extrusion speed limits.