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What is an RA finish?

by Rhyley Bryan

What is an RA finish?

Ra is the arithmetic average of surface heights measured across a surface, Ra surface finish. Simply average the height across the microscopic peaks and valleys. Surface roughness can be measured by a profilometer, a surface profile measurement tool.

How do you calculate Ra surface finish?

Ra is calculated as the Roughness Average of a surfaces measured microscopic peaks and valleys….That means you:

  1. Measure height across the microscopic peaks and valleys.
  2. Calculate the SQUARE of each measurement value.
  3. Calculate the MEAN (or average) of those numbers (squared).
  4. Find the square ROOT of that number.

What is a 30 Ra finish?

One of the popular finishes is the Ra 30 surface finish or the #4 finish. It is also known as satin finish. It is an electronic polishing method and produces very low roughness. Hence, it is a very fine finish used in a variety of industries. It exhibits a 180-grit grain, which renders a dull finish.

What is a 20 Ra finish?

20 RA – 12 RA) #7 Finish. Smooth buffed finish with a very bright appearance. Light haze. The part is belt polished with a 280 – 320 belt then buffed with a cut and color compound.

What does RA stand for in polishing?

Ra stands for Roughness Average. In past years Ra was also known as Center Line Average (CLA), or Arithmetic Average (AA), but today Ra is the most commonly used surface finish parameter in the steel industry.

Which is the better surface finish or RA?

One can infer from examination of the formulas, that a single large peak or flaw within the microscopic surface texture will effect (raise) the RMS value more than the Ra value. The electropolishing process may improve a surface finish by up to 50%.

What Ra is a #4 finish?

A standard #4 finish could be about 0.8 (32) Ra, while a #4 Dairy or Sanitary finish have an roughness average between 0.3 (12) Ra and 0.4 (16) Ra.

What does RA stand for?

Rheumatoid arthritis
Rheumatoid arthritis (RA) is a disease that leads to inflammation of the joints and surrounding tissues. It is a long-term disease.