Surface finishes

Fine Tubes manufactures high quality metal tubing for a range of applications where surface finish is critical to the correct functioning of the product. Whilst a surface can feel smooth to touch, when examined under a microscope the true story may be quite different. The qualities of the actual surface are the result of various manufacturing technologies, lubricants and cleaning processes.

Controlling and measuring the surface texture or roughness of precision tubing is an intrinsic part of our production process. We use values for roughness (R), waviness (W) and form (F) to categorise engineered surfaces.

Typical Standards

The following industry standards provide guidelines for roughness that our products meet, and exceed:

BS 1134:2010 Assessment of surface texture - guidance and general information
ISO 4287-1 Surface Roughness Terminology Part 1
ANSI B46.1 Surface texture, surface roughness, waviness and lay

Useful definitions

Ra Roughness average is the universally recognised and most used international parameter of roughness. It is the arithmetic mean of the absolute departures of the roughness profile from the mean line. Ra is reported in microns.
Rq or RMS Rq is the Root Mean Square parameter corresponding to Ra.
Rp The roughness peak is the maximum height of the profile above the mean line within the sampling length.
Rt Roughness total is the maximum peak to valley height of the profile in the total  assessment length (L).
Rz Rz = (Rp +Rp) within the sampling length.
Rv The maximum depth of the profile below the mean line in the sampling length.
AA Arithmetic average
CLA Centre Line Average, this is Ra expressed in micro inches.

Roughness Indicator

Roughness Number Comparison
'Rugotest. 3'    
Ra Ra CLA
μm μinch
No. 1 0.0006 0.25
N0 0.012 0.5
N1  0.025 1
N2  0.05 2
N3  0.1 3
N4  0.2 4
N5  0.4 16
N6  0.8 32
N7  1.6 63
N8  3.2 125
N9  6.3 250
N10  12.5 500
N11  25 1000
N12  50 2000
N13  100 4000
N14  200 8000

This example outlines a typical reading on a 25.4mm OD x 1.30mm wall Ti325 seamless tube:

Ra = 0.326 μm
Rq = 0.421 μm
Rz = 2.820 μm
Rt = 3.795 μm
CLA =   13 μ”

Roughness Parameters

The root Mean Square (RMS) roughness (Rq) is the root mean square average of the roughness profile ordinates.
Note: Rq is also called RMS.

Roughness Depth

The Single Roughness Depth (Rzi) is the vertical distance between the highest peak and the deepest valley within a sampling length.
The Mean Roughness Depth (Rz) is the arithmetic mean value of the single roughness depths of consecutive sampling lengths.
The Maximum Roughness Depth (Rmax) is the largest single roughness depth within the evaluation length. The units of RZ are micrometres or microinches.

Please click on chart below to enlarge.

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