Y-Axis partly Waves/Ripples

As you can see on the photo I have a problem with waves from a certain point on the y-axis.
I have used my Mendel after a long time, before I did not have this problem.
I have already tensioned the belts and tightened all screws.
Any idea what could cause this problem?
I had these ripples in the front part of the Y-axis in all models I tested.

Thanks
Lars

So this object was printed with the long sides parallel to the Y axis and the end at the front of the bed has waves?

I would suspect one of the linear bearings has failed. Perhaps if you move it by hand with the power off you can feel it.

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[www.hydraraptor.blogspot.com]

Thanks for the feedback.
Yes it was the Y axis and then from the middle to the front, i got this waves.
I will check each linear bearing on all axis, might be anyway a good idea after years of using.
And replace them if necessary.
Lars

I clean my bearing before use using a You-Tube video I found

Great Bearing Cleaning video

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Computer Programmer / Electronics Technician

If new linear bearings don't resolve the issue, I would thoroughly inspect the printer to rule out worn out or loose parts, particularly the printed plastic parts.

I'm actually in the process of rebuilding and updating my Mendel90 with a full set of new plastic parts printed in Polymax PETG. I found that many of the original ABS plastic parts showed signs of fatigue and when I came to disassemble my printer many of the plastic parts crumbled, meaning my printer was probably a lot less sturdy than it once was! It's worth mentioning that I originally self-printed the plastic parts and the filament I used may not have been the best quality.

I purchased a full set (plus spares) of linear bearings from e3d-online.com and can confirm they are of good enough quality, at least as far as these low-cost bearings go.