Marlin Adjusting feedrate I'm using the Marlin firmware (1.1.0-RC7 - 31 July 2016) for a 3d printer. Currently the printing is not perfect due to slight inaccuracies in movements along the x and y axis. I'm trying to change the feedrate for speed along the xy axis whilst the printer is in operation to make sure the printer stops on time and prints accurately.

I have some code for controlling the feedrate but the problem is that I'm not sure where I am supposed make these adjustments. In the configuration.h file I see this code: (lines 742 and 753 )

/*line 742*/ #define HOMING_FEEDRATE_XY (50*60) 
/*line 753*/ #define DEFAULT_MAX_FEEDRATE {300, 300, 5, 25}  // (mm/sec)


I'm probably misunderstanding something but it seems like this sets the feedrate to a default value which is the same as the maximum. 

If the feedrate changes during printing I'm guessing it would be done in Marlin_main.cpp but I'm not sure which part it actually changes. Can someone point me in the right direction here?
You can change the maximum allowable feedrate in Configuration.h, but the actual feedrate that is used isn't determined by your firmware. The feedrate is specified in the G-Code file. A command like

G0 X10.0 Y15.0 Z3.0 F9000


indicates a move to (10,15,3) at a feedrate of 9000 mm/min. If F is not specified, the last used feedrate is used.

You just have to provide the appropriate G-code commands with the feedrate you want in them. There's no reason to modify the firmware to get a different feedrate.