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OH MY FUCKING GOD
PSA for anyone who interacts with US Woodworking Online Content while Living Outside The USA: “600 grit” is not “P600”, but, like, “P1200”.
THERE’S A SEPARATE IMPERIAL (sorry, US Standard) UNIT FOR SANDPAPER GRIT
i’m so fuckin steamed right now
Grit (both CAMI amd FEPA) is based on the size of the grains that pass through a series of increasingly fine mesh sieves, with the numbers representing how many holes per a given area there are in the sieve. However, the size of those holes depends on both the density of the wires and the thickness of the wires (thicker wires = smaller holes if you have the same density of holes), so I would imagine that the two standards diverge because of that. I don’t know for sure though, and those standards are expensive to buy
I don’t think you could use SI prefixes with the grit systems, but ultra-fine sandpaper often abandons the grit systems and just gives you an average size of grain in micrometres
its the same at the low end 60 = p60, 120 = p120 but then it diverges. Odd. Can I still use SI prefixes with it? milli-P giga-P?
Grit (both CAMI amd FEPA) is based on the size of the grains that pass through a series of increasingly fine mesh sieves, with the numbers representing how many holes per a given area there are in the sieve. However, the size of those holes depends on both the density of the wires and the thickness of the wires (thicker wires = smaller holes if you have the same density of holes), so I would imagine that the two standards diverge because of that. I don’t know for sure though, and those standards are expensive to buy
I don’t think you could use SI prefixes with the grit systems, but ultra-fine sandpaper often abandons the grit systems and just gives you an average size of grain in micrometres