What does the Ra value tell us about the quality of a surface?

In our daily business we often notice that there is a mixture between roughness value and surface quality. Usually a material should be selected for a specific application. The Ra value is used as a specification. But is this sufficient? We would like to explain it!
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[@realityamoh1001]

Thank you Sir! I learnt something new, especially on the cleanability.

[@rkhh01]

On your interesting video you show 4 example surfaces, all with the same Ra of 0,5 micron. The first is easy to clean, the last not.
1. What about the other two?
2. What roughness measurement system should be used instead of Ra to know which of these 4 types of surface (or other types) a tube internal diameter has?
3. Intuitively the third type in the graphic (flat plateaus and deep "V" valleys) looks least easy to clean - at least for very small residues - and maybe the second most attractive for biofilm.. do you have cleanability comparisons you can share? The available literature is very inconclusive - I think because most tests have been based purely on Ra and have not considered surface quality.

[@sampathdhadake8959]

Thank you sir

[@ViktorTools]

At the end of the day it is good video

[@techquirks707]

😂