Need Help! Dimensions Problem Please

Hello,

I have finished my DIY CNC router for wood working and I am using Mach3 software with it. But I have faced a problem which is that there is a difference in dimensions between designed dimensions in CAM software and executed dimensions on the machine. The difference are 8 mm increment in Y axis and 6 mm increment in X axis.

I mean that I draw a square ( width = 10.00 cm ) on CAM software ( like Artcam & Vectric Aspire ). After finishing the job on the machine and when I measure the dimensions of engraving square, I find them are 10.8 cm ( in Y axis) and 10.6 cm ( in X axis ).
Or if I make a circle diameter 25 cm, the measured diameters after engraved are 25.9 cm ( in Y ) and 25.68 cm ( in X ).

I have used:
KL-5056D Digital stepper drivers .... from Automation Technology Inc
SFU1605-C7-1055 Ballscrews ..... from Automation Technology Inc


In Mach3 settings, I have set the value of ( steps per unit ) in motor tuning as the following :
( 200 * microstep of uses drivers )* (1 / ballscrew pitch in mm)
( 200 * 2 )* 1/5 = 80

And then I have set the axis calibration from ( alt + 6 )as usual.
But the problem still exists.

Can any one help me ? How can I cancel this increments ?

Thanks a lot for any help..