Lossing accuracy when printing

I am currently printing files such as moulds and other parts that are required to line up together and i am having issues with them lining up. The models line up perfectly fine in the modeling software but when I print the file, the real thing is a different story. The y-axis seems to start off by 1 to 2 mm, it may not seem like much but it really affects the result. The printer only has approximately 96 hours of printing time.

does anyone have any suggestions on how I can troubleshoot this? Could it be an issue with the belts losing tension, if so are there any tutorials I can follow to fix it?

Print a calibration cube and check dimensional accuracy and squareness

have printed a 20mm one and everything seems to be in the 0.20mm range

Why not design your own cube with a shallow square hole in the bottom, and a matching square protrusion on the top? Then print two, and mark the axis orientations on the build plate. Then:

  1. Measure everything with a caliper. Is everything correct and the same on both cubes?
  2. Do the cubes fit together?
  3. If so, do all four sides line up, or are the cubes offset?
  4. If not, is the hole or the protrusion wrong? On which axis?
  5. Are the errors/offsets consistent on both cubes? If not, look into why that might be.

Once you get some hard data, you can look into what on your printer might need adjustment/tightening.

Good luck.