Parallels, Surface Finish & Hardness

Surface Finish

Any machined component has a surface geometry which consists of three basic elements:

Form or Curvature - Whether the surface has irregular bumps or dimensional changes
Waviness - Whether the surface has regular repetitive ripples or patterns (e.g. milling patterns)
Roughness - The shapes or irregularities that are smaller than, and form part of the waviness pattern (e.g. material micro-structure)

Waviness and roughness are traditionally the most difficult elements to measure when comparing surface finish, however, they have a radical effect on the performance of the finished component. Variations will cause aesthetic appearance changes, component wear variations, oil retention variation etc. Many manufacturers therefore specify a range of roughness values which their components should be manufactured to, often expressed as: Ra, Rq (RMS), RzDIN, Ry, Sm,mm