Steps per unit are calculated, but, you should actually see that the movement agrees with the calculated value over some working distance , and if not, then tweak the step value.
You can use Mach to accomplish this quickly, open the SETTINGS SCREEN>SET STEPS PER UNIT...AXIS CALIBRATION located by the reset button. ( use is covered in the manual)
1/12700= .00008" per step ( if life was perfect )........ .00008 x 76.66= say .006" change .......so run the calibration and forget the
" should work" thinking
I would then also just check the accel and velocity and reduce max velocity to say 50 to 70% of max velocity
You should not need to scale up the Step Pulse as usually the driver manufacturer provides info for it.
RICH
BTW, I don't know who Mr Stephenson is but I am sure he had reasons for saying whatever based on his discussions with you.