Strange lines in the bottom

Does anyone know why I get these lines the bottom
The material is walnut

yes, your router is not perpendicular to your wasteboard + it seems like your Z is slipping somewhere which leads to inconsistent depth.

that’s my guess anyways

I have tested it and it seems ok
I did a same type of clock last week
and that one was ok
I used the same bit both time
a downcut bit

make sure that your spoilboard is flat and surfaced

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No., but that was a good idea
I´ll buy that later

What kind of vertical play do your Z have? If you weight down the router 2kg how much do it deflect downwards?