Acta Polytechnica Hungarica Vol. 11, No. 5, 2014 – 5 – The Mysteries of the Surface First Part: The Characteristic Features of the Microgeometry of the Machined Surface Béla Palásti-Kovács, Sándor Sipos, Szabolcs Bíró Bánki Donát Faculty of Mechanical Engineering and Security Technology, Óbuda University, Népszínház u. 8, H-1081 Budapest, Hungary; e-mail: palasti@uni-obuda.hu; sipos.sandor@bgk.uni-obuda.hu; biro.szabolcs@bgk.uni-obuda.hu Abstract: In these days, the key elements for the reliability and the safe operation of technical devices are the following: surface of the tools, the surface quality and the roughness of the connecting elements. The present work is going to introduce the idea that different machining methods that create microgeometries that are very much different from each other and of diverse roughness parameter proportions. It will be shown that the wear and the change of the tool edge(s) ‒ resulting from the deterioration process of the tools, used during production ‒ cause significant arithmetical, average and form deviations. The uncertainties of the roughness measuring technique, arising during the evaluation of the real and filtered surface profiles, will be shown via samples. Keywords: machined surface; microgeometry; roughness; wear process 1 Introduction Production, quality and operations — terms, being inseparable, depending on each other and mutually determinant of each other. Each specification and problem, arising during the production process of connecting components, may have a significant influence on the operation. This research work has been oriented to examine surface microgeometry by a skidless stylus method, to the modernization and extension of the evaluation possibilities of the surface profiles and topographies, gained from measurements at Bánki Donát Faculty of Óbuda University, for more than three decades [1-4]. The research and development works started in 1975, with a surface roughness measuring device, type “Kalibr 201”; the first evaluation programs in FOKAL programming language run on TPA computers. The set of devices of the research work has now been significantly updated. We have workshop machines, works