Build your own CNC machine.DIY

Salam and hi friends.

I am going to write this article about my homemade cnc for those who want to build there own  CNC machine. So first of all let me tell you that what is a cnc machine? CNC mean Computer Numerical Control. A cad software generate tool paths of any design and then it export it into Gcode. Then this Gcode read by a software called cam software like mastercam, cambam, match4 etc so these software read the Gcode and it send the data to CNC driver board and drive board runs the CNC machine.
My CNC is not much advanced but it is great for my works. I have built this CNC for cutting wood,stone/marble, copper, aluminum and iron but unfortunately i got backlashes in bearings. So it can't cut very hard materials such as stone copper and iron but it is good for wood and aluminum and also it is very good for plasma cutter because in plasma cutter there is no friction between material and plasma torch so it will run smoothly. 
Now let me explain that which materials i have used for my CNC machine? the base of my CNC is made from  0.5x1.5 inch rectangular iron pipe and i have joint them using welding plant. 

For sliding i have used window sliding bearings and these bearings slide on iron rods these rods welded on 1.5x 3 inches rectangular iron pipes. i am using total 16 bearings for sliding. 8 for X axis 4 for Y axis and other 4 for Z axis. But please keep in your mind that if you are going to use same bearings so first you have to check the quality of bearings because when first time i bought these bearings so there were no backlashes in them. After i put some presser on them so i found backlashes in these bearings. So before you plane to build your own CNC so you should buy good quality bearings. 
So how X,Y and Z axis move foreword and backward? I am using two 36 inches threaded rods for X and Y axis and one 14 inches for Z axis. And each threaded rod have two nuts one move the arm foreword and second pull it backward. Each threaded rod is connected with a stepper motor which spin the threaded rod clockwise and anticlockwise.