Z axis - back to 8mm studding - need help

hello all, this is my first post and my first 3d printer :-)

but i have a problem...

I have bought a perusal i3 with Z axis trapazoid screws but the screws won't screw in to the brass nuts to operate the Z axis - so as a quick fix i fitted M8 MS studding and built the printer up until replacement lead screws arrive.

my problem is that the Z axis calibration is wrong , 10mm travel is actually 6mm because i have studding and not the course threaded lead screws.

does anyone have firmware that is setup for 8mm studding ? or how do i change the travel parameters.

thanks all

mike.

Setup

Perusa i3
OSX
sd & usb connectivity.

okay it seems the config.h needs to have the steps changed from

#define DEFAULT_AXIS_STEPS_PER_UNIT {80,80,4000,500} // default steps per unit for Ultimaker
Where these are the steps/mm for X,Y Z and E axis

to

#define DEFAULT_AXIS_STEPS_PER_UNIT {80,80,2650,500} // default steps per unit for Ultimaker
Where these are the steps/mm for X,Y Z and E axis