Specifications will set an acceptable degree of roughness, but there's more than one way to measure the surface, and more than one way to quantify the measurement results.
Ra stands for roughness average.
Ra is a average of only peaks; therefore, to get an Ra, multiple your 3. This thread has continuing errors so it was very hard to follow.
We went back and added this anachronistic running commentary based on clarifications by subsequent readers: RMS and Ra measure two different things, so there is no actual conversion factor.
But for sine wave roughness the factor would be 1. Later readers also noted that RMS is usually expressed in microinches whereas Ra is usually expressed in microns; but this is not universally true either, which adds to the confusion: The ratio is not 2: I am afraid you will find that I am correct.
Please let me know if I misunderstood your comments. Still a nice website for information on finishing. Keep up the good work. Michael Herron ceramics - Golden, Colorado I agree. Also note that outside of the US values are generally expressed in microns: Regards, electropolishing - London, England Ra value means roughness average in microns whereas RMS means root mean square value in micro inches so if you know the conversion from mm to inches you have the answer with you.
Charuhas - India Anachronistic running commentary: This is apparently incorrect because Charuhas has omitted the 1. Write the result in standard engineering form: This is incorrect in step 1 because 0.
The conversion factor 1. The ratio for saw tooth profiles is closer to 1.• resolution between peaks, • selectivity relative to preceding peak, • skew, and • excess The mean value, the standard deviation, the relative standard deviation and the confidence interval are calculated. You can set limits for either standard deviation, the relative standard deviation or the confidence interval for each of these parameters.
Graphically, Ra is the area between the roughness profile and its centerline divided by the evaluation length. The evaluation length is normally five sample lengths where each sample length is equal to one cutoff length.
Ra is by far the most commonly used Surface Finish parameter.5/5(5). Evaluating System Suitability • peak tailing, • capacity factor (k´), • plate numbers, • resolution between peaks, • selectivity relative to preceding peak, • skew, and • excess The mean value, the standard deviation, the relative standard deviation and the confidence interval are calculated.
Arithmetical mean height (Ra, Pa, Wa) Arithmetical mean height indicates the average of the absolute value along the sampling length. When dealing with the roughness profile, Ra is referred to as the arithmetic mean roughness, while Wa is referred to as the . A roughness value can either be calculated on a profile (line) or on a surface (area).
The profile roughness parameter (Ra, Rq,) are more common. The area roughness parameters (Sa, Sq,) give more significant values. Profile roughness parameters. Each of the roughness parameters are calculated using a formula for describing the surface.
A COMPARISON BETWEEN 2D AND 3D SURFACE PARAMETERS FOR EVALUATING THE QUALITY OF SURFACES the arithmetic average of absolute values, Ra for 2D evaluation and Sa for 3D evaluation, - the inferior deviation related to the average value as calculated for n measurements.