Heavy Layers on the surface. Belttension?  

Heavy Layers on the surface. Belttension?

Hello, I have a lot of deep lines on the printed parts. At first, only half of the surface was affected by these lines. After checking the belt tension, I saw that they were too tight (about 135 Hz). I reduced them to the optimal 85 Hz on both belts.
After that, I did a new test – and look: now the entire printed part has these horrible surface lines.

In the picture, you can see the printed parts on the left side at 135 Hz. One half looks good, the other half looks bad.
On the right side, you see the parts printed at 85 Hz – the surface is completely bad. The flow is correct (maybe just a little bit too low...), you can see it in the picture below.

I also contacted support, and we checked the alignment of the Z-spindles to make sure nothing is rubbing against printed or metal parts during movement. We loosened the screws of the trapezoidal spindle – but the surface is still bad during prints...