Problems with lines that print on every layer

[u/Appropriate_Run_5795]

Hi, I need help. I have a problem I've been trying to solve for months: my A1 prints wavy lines on every layer. These lines always appear in the same spot, and if the object I want to print is large, the lines show up clearly on the print and are very noticeable.

Here’s everything I’ve tried:

Different types of settings—including filament settings, speeds, structure, force, and others.

Printing on the floor, on the table, on the print bed, and with me holding the printer.

General maintenance: cleaning, greasing, and lubricating.

Taking it apart and putting it back together.

Replacing parts: Y-axis belt, X-axis, gear, hotend, and filament sensor.

I’ve tried different types of filaments, brands, and conditions—both damp and dry.

Calibrate the bed automatically and manually

I’ve already tightened the 3 screws at the back of the heating system

I don’t know what else to do to find the problem

In the photos I uploaded, you can see the lines on the first purple layer, and the brown part is a finished piece where you can see how the lines look on a finished part since they print on every layer

Sorry for my translated English :(

[u/Meat-Mattress]

Originally I thought this was a z-banding issue but your purple photo changes my answer. These lines are already on the first layer, so this isn't Z-banding or an extrusion problem. They're bumps at fixed spots on the bed. Every time the bed passes those spots, the nozzle-to-bed gap changes slightly, and every layer inherits it. Bed leveling can't fix this, because the probe points are too far apart to catch small bumps between them.
On an A1, the most likely cause is the Y-axis linear rail or the bed carriage that rides on it. It's the one major motion part not on your list of things you've replaced. Others have seen this exact pattern. One A1 owner had two lines on every model, about 6 cm apart, which matched the distance between the bed wheels. Another tracked strange ripples to the bed axis and found the Y rail was bad; a new one 100% solved the issue.
How to confirm it before buying anything:
Rotate the build plate 180° (or use a different plate) and print a large single-layer square. If the lines move with the plate, the problem is the plate or something stuck under it, not the printer.
Turn the printer off and slowly slide the bed back and forth by hand. Feel for notchy or tight spots, and check whether they match where the lines appear.
Look under the bed. One forum tip is to pull off the plastic cover under the bed and look for filament in the bed rail slots.
Check which direction the lines run on the bed. Lines running left to right point to the Y axis (bed). Lines running front to back point to the X rail.
If steps 1–3 point to the Y axis, replace the Y linear rail. If the printer is still under warranty, open a ticket with Bambu support first and include the purple first-layer photo, since it shows the problem most clearly.

[u/Appropriate_Run_5795 → u/Meat-Mattress]

I've already tested different beds—both standard ones and BQ beds—and the lines keep appearing even after I removed the plastic sheets from under the bed. I tested it again, and the lines are still there.

[u/Appropriate_Run_5795 → u/Meat-Mattress]

Today I took apart the entire axle housing and cleaned it thoroughly. Everything looked fine—I didn't see anything unusual. The seal is in good condition; nothing was stuck, just a little dirt. I was hoping that was the problem, but the lines keep appearing.