Accurency for 2 step motors

Hi, i have a home made router. The y axis has two step motors nema 34, every works ok, bit i have 4mm diference in 2440mm travel from one side to the other. Each motor has its oun Power supply and DRIVER and the signal from the controler (pulse and dir) ( controler DDCSV1.1)are conected in paralel to the DRIVERS
I allready switch the motors and drivers and is the same 4mm diference.
Change the transmision is not posible because is so small the
Diference.
Does any body can tell me what to do or some tips to do.
Thank you all.

Flute:
The y axis has two step motors nema 34, every works ok, bit i have 4mm diference in 2440mm travel from one side to the other.

How are the motors driving the part that moves? Perhaps through lead screws?

When you say there us a 4mm difference, is that for an identical number of steps for each motor?

Are you taking backlash into account? In other words does the 4mm difference exist when you have taken backlash out of the system?

Is the error always exactly 4mm +/- 0.01mm (or whatever is the resolution of your machine)? If it is not always exactly the same I suspect one drive has more friction and the motor is missing steps.

And if the error is always the exact same I would experiment with changing the number of steps per millimetre

...R
Stepper Motor Basics
Simple Stepper Code

Its better to wire the motor windings in series and drive with a single driver - that way you get the same current in each, and effectively they are coupled whatever the electronics does.

You might be getting interference in your step pulses (its best not to route logic clocks and pulse signals very far, although opto-coupling will definitely improve reliability for this).

Never route logic signals alongside high current wiring if at all possible. What drivers are you using? Are they
optocoupled?
(please always post links for each piece of hardware you mention, details always matter).