Why such a large discrepency on the print time calculated in the G-Code view and the actual print time in Repetier?
Usually it’s accelleration. The gcode defines the “max” speed, but the firmware in the printer slows down in corners because the extruder can’t actually change directions at full speed - it would skip teeth on the belt and/or bounce around. So the actual speed depends on how close to the max speed the printer can come, based on the geometry of the part being printed. If you print a large box with flat sides, printing speeds will be close because it’s mainly long straight lines. If you print something with lots of tiny detail, the printer will never get to max speed.
The guys who wrote the Sailfish firmware wrote a program that runs on the desktop that uses the firmware’s accelleration code, so it gives precise numbers, which they wrote to test the software, so it’s possible to get precise print time estimates on a desktop, but you’d need such a tool for your firmware, with the same configuration parameters.
It’s not just repetier, it’s all hosts. This is just one of those things that is difficult to calculate correctly.
Exactly. All hosts know the theoretical print time as if the printer had infinite accelleration. In reality, printers are only able to accellerate at a finite rate (F=MA) so the actual print speed is always (on average) slower than the print speed in the gcode, so the print time is always longer than computed by the slicer.
Slicers could incorporate knowledge of accelleration into their print time estimates, but they don’t.
So the result is that real world print times are very roughly 2x the estimated print time. Varying widely depending on the specifics of the printer and the piece being printed.
Thanks guys, answers my questions.
I know in repitier, in printer options, there is a setting to adjust the estimated time.
the closer you get to a zero ramp up time the closer your time estimates will be.
Do feel bad though. Even in professional 20K cam packages the time estimate is worthless most of the time without heavy tweaking.
The irony is that the firmware knows exactly what the printing time will be, to within a fraction of a second.