What Grit Size Is Needed for Certain Finish?

This is a very common question.  We all know that the bigger the grit size the bigger chunk or pit (imperfection) applied to the material.  That imperfection is rated and given an RMS or RA number.  Below we have a quick chart to show you what the expected finish of the material should be when using a particular grit size.  These finishes can vary according to the type of material,wet or dry grinding, RPMs, depth of cut among other application details.  Once past the 600 grit, the finish goes into more of polishing grin instead of a material removal grind which would require a much finer polishing grit (1000-2000).

Eagle Grit Size Eagle Grit Size Expected RMS
Finish Resin
Expected RMS
Finish Plated
60 251 35-50 -
80 181 20-30 90-125
100 151 16-24 64-90
120 126 14-20 48-64
150 107 12-17 32-48
180 91 10-15 24-32
220 76 8-12 20-24
240 64 7-11 16-20
320 54 6-10 14-16
400 46 5-9 13-14
600 30 3-8 12-13