Untitled Gardening Project #11

The exit side of the holes drilled into the discs will tend to have fairly heavy burs. The exit side won't be visible upon completion, so there's no need to worry about preserving the finish; a few swirls on 180-220 grit carbide sandpaper will take the burs right off.

Don't sand the light burring on the upper surface; finish is important here and later finishing steps will take care of it.

An aluminum surface will have its own aluminum oxide layer of the same hardness as the abrasive on 'standard' aluminum oxide sandpaper. This isn't a big deal for coarse grits like 100-300 where the abrasive will gouge much deeper than the hard oxide layer into the soft aluminum underneath, but for later finishing steps where we'll be removing mill lines and polishing to a mirrored finish with 500-2000 grit, it will be essential to use silicon carbide otherwise the effort will be wasted.