Assume a small bore hole with a few mm diameter in a hard plastic plate (e.g. POM), and further assume that after drilling the hole the surface of the plate is grinded with a disk with fine sand paper (e.g. 20 µm mean grit diameter). This would remove a possible larger radius from the edge of the bore hole and sharpen it to a certain extent. How will the final shape of the edge of the bore be affected by the grit diameter?


  1. Is it under this conditions reasonable to assume an approximate fillet radius of the bore hole's edge in the same range as the particle radius of sand paper?
  2. If not, is the expected fillet radius more likely to be larger or smaller than the particle radius?
  • $\begingroup$ It is not expected that the fillet would have a constant radius! $\endgroup$ Commented Nov 6, 2019 at 13:53
  • $\begingroup$ Yes. But the shape could be approximated by something like a radius. That is why I asked for an "approximate fillet radius". $\endgroup$
    – Georg W.
    Commented Nov 6, 2019 at 14:33
  • 1
    $\begingroup$ You can finely polish a large radius or a small radius with a very fine grit... $\endgroup$
    – Solar Mike
    Commented Nov 6, 2019 at 14:58
  • $\begingroup$ In my imagination the edge of the bore hole ideally has a zero radius before grinding. I should clarify that grinding of the surface happens with a flat grinding disk. That means there edge of the bore hole is even sharpened by grinding if there would be a noticeable radius before grinding. $\endgroup$
    – Georg W.
    Commented Nov 6, 2019 at 15:14


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