Problem with x axis caliberation

Hello everyone,
I built a cnc/3d printer out of 2040 t-slot aluminum
It's intended for light cnc work, engraving mdf ,foam or acrylic.
The design is similar to most of 3d printers with dual nema 23 steppers z axis
Nema 17 for both the x and y
For the cnc electronics i'm using a bob with parallel port and single axis tb6560 for both x and y
and tb6600 for the dual z steppers
I'm using bearing blocks and smooth shafts for all axes with gt2 belts and 20 teeth pulleys on the steppers
After completing the build and wiring I started caliberating the motors in mach3
The problem is with the x axis
the micro stepping is at 1/8 and it should be 40 steps /mm
After using auto caliberation function in mach3 and measuring the travel with a ruler ,every time I get a different travel
I tried tensioning the belt, loosening, vibration dampners for stepper, switching nema 17 motors,using nema 23 stepper ,switching drivers, changing idler nontoothed pulley with a toothed one and even using a new parallel cable. Still I get different reading every time I caliberate
I did few test pieces on plywood and the all came out with deviations in the x axis which are not consistent
Is the problem with the design or what
I have been trying to fix it for over a month to no avail.
Thanks.

Do you have to use the autocalibration? What were the results of calibration? Less or more steps/mm?
Did you try to hardcode the 40steps/mm?

How smooth does the X-axis run? Do you feel any binding?

Quote
o_lampe
Do you have to use the autocalibration? What were the results of calibration? Less or more steps/mm?
Did you try to hardcode the 40steps/mm?

How smooth does the X-axis run? Do you feel any binding?

I used auto caliberation on the y (also with belt and pulley) and on the z axis (lead screw) and got accurate results
The caliberation of x gave 42.1 steps /mm
As I auto caliberate it never gives me the same result
If I send it to 150 mm it may give 150 mm
If I do it agin the results are never the same 149 ,152.5 or whatever
I recaliberate again and again and nothing changes ,the same inconsistent travel continue.
What is hardcore the 40steps/mm?
Thanks for your reply.

Do you have backlash in the X-axis? That would explain the errors. Maybe a loose screw or an axial coupler that allows a little compression?

Hardcode X-steps means, you set the X-steps manually in firmware instead of autocalibration.