**4. Conclusions**

Chatter vibration and surface roughness resulting from the pocket milling of aluminum alloy thin plates without back support are studied. This situation of low rigidity is common between vacuum cups in flexible fixtures that support thin floors. Aiming to determine the conditions under which a milling in a situation of such a low stiffness could be stable and feasible, vibrations during machining and final surface roughness are measured and analyzed. SLDs are calculated, as well as the FFT of the vibration and the FFT of the surface roughness.

Main results and practical recommendations can be summarized as follows:


**Author Contributions:** Conceptualization, M.C., A.R.-M. and F.V.; Data curation, M.C. and A.R.-M.; Formal analysis, M.C., A.R.-M. and A.L.; Investigation, M.C., A.R.-M. and A.L.; Methodology, M.C. and A.L.; Project administration, A.R.-M. and A.L.; Supervision, A.L.; Validation, F.V. and A.R.-M.; Writing—original draft, M.C. and F.V.; Writing—review and editing, M.C., F.V., A.R.-M. and A.L. All authors have read and agreed to the published version of the manuscript.

**Funding:** This research has received funding from the ELKARTEK program of the Basque Government within the project OPTICED, grant number KK-2021/00003.

**Institutional Review Board Statement:** Not applicable.

**Informed Consent Statement:** Not applicable.

**Data Availability Statement:** Data available on request from the corresponding author.

**Conflicts of Interest:** The authors declare no conflict of interest.
