Want to Achieve a Specific Metal Finish? Your Abrasive Product Is Key  

By Elliot Shepherd, Associate Product Manager, and Ron McCarthy, Abrasive Specialist, Weiler Abrasives Group

A part surface may require a specific metal finish for many reasons — including cosmetic, functional or customer preference. Certain metal finishes can also help the material resist damage or rusting.  

Some fabrication and manufacturing applications require a precisely measured finish on metal parts, while others need only a subjective or visual finish. On many jobs, consistency of surface appearance is the most important factor in judging a metal finish. 

The abrasive product used for the job, the grit type and size of the abrasive grain, and the operator technique are all variables that affect surface finish and can produce different results.

Understanding Metal Finishes  

Metal finishes can be measured (commonly called Ra for roughness average or RSM for root mean square) or subjective (also called visual finishes). Metal surfaces may appear smooth to the naked eye but actually, contain peaks and valleys. With measured finishes, the roughness of the surface is measured with a profilometer, which determines Ra values by moving a diamond stylus across the surface for a specified distance and using a specified contact force. The Ra value is assigned as an average of the surface deviations. A low number represents a smoother or less deviant surface.

While less common than visual finishes, measured finishes may be needed in applications where two parts come into contact with one another and require a precise, smooth finish to avoid friction. Measured finishes are also used in food-grade or aerospace applications that require stringent quality testing.

In applications where the material will be powder-coated or treated, the finish may not be as critical, and a subjective finish is often acceptable. Still, if a part will be painted, it should be relatively free of deep abrasions, which lessens the chance of them being seen after painting.  

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