Laser changing position on it's own

When doing the same image on multiple pieces the image moves location on its own. The only thing I do is start the burn, change the piece, start the next burn, and so on. Why is my image moving on its own? I did 3 runs with no problem but the fourth run moved down about 26mm. Any help would be appreciated.

One or both of the motors are skipping steps. If it moved down only, then it’s likely the Y axis. Either the current is not set high enough, or the acceleration value is too high. Both of these settings are in the config.txt file on the C3D’s SD card.

Oz, thanks for the quick response! I don’t think I explained my issue clearly. I am marking steel pins with ID numbers but I only do 1 pin at a time. So I set up one pin, hit start, the laser etches the numbers, and returns to home position and shuts down when done. Then I remove that pin, place the next one and do it again. So the machine cycles 1 complete-time every pin. For some unknown reason, the placement of my numbers changes on its own, I did 3 pins and they came out fine when I did the fourth one the numbers moved about 25mm’s on their own as you can see in the pictures,C,D,E, are perfect, on F the numbers drop about 25mm’s. I didn’t change anything other than the pin.

, Sorry for the confusion.