Wavy skin at the base of the piece

Support & Troubleshooting Form 2
#1

On some prints, i got a wavy skin at the base of the piece.

( https://flic.kr/ps/3Xc26o )

Somebody knows why it happen and how to avoid this ?

Thanks,

#2

You need to clean your optics(mirror, glass window, galvo mirrors)

#3

OK, thank you very much !