This is not my original idea, however I feel it's appropriate to the content of the blog and an old, simple tech that should be known by the mentality retarded humans that exist today. Strong hide glue, wood stick, or flat block. Find sharp gravel stone, sand, or any other grit of the abrasive material you need.  Heat the glue, add to stick liberally. Sprinkle on abrasive, and pour on more glue. For a coarse grit, make a pool by carving out wood then pouring glue. Add a consistent  sized abrasive and pour on more glue. Let dry. You can also use a rounded sand stone for a wood file or sand papper. Round on concrete or another rock.