I worked an internship at a machine shop and ever since then, I have been suffering withdrawal from the availability of precision measuring equipment especially the large granite surface plates we used for doing Quality Assurance checks on parts.
I find myself sharpening with a variety of different methods including scary sharp (sandpaper on a flat surface). While I have both plate glass and 12”x12” granite tiles that work perfectly well for this purpose, without a dedicated table for sharpening I often find that my sandpaper and surface plate are buried beneath a pile of dull chisels and wood chips.
I decided to make a cast concrete table dedicated to tool sharpening. If the cast concrete surface finish was good enough, it could be used directly as a surface plate for sharping with sandpaper. If the concrete did not work out, then it would make a heavy and durable table-top on which to place my granite and glass.
The legs and stretchers are fabricated from 1” square steel tube and welded together with a flux core, wire-feed arc welder. The stand was supported inside of a particle board mold that was caulked and painted to give the smoothest possible finish then the mold was filled with fiber reinforced concrete and vibrated to remove air bubbles.
After 24 hours or so, the mold was disassembled. Surprise! I took the mold apart too soon and was left with two ugly blemishes on the surface where the damp concrete stuck to the mold during removal. I attempted to sand the surface down to level the blemishes but the blemishes proved to be too deep to be completely removed. I sealed the surface of the concrete table top with glossy chemical sealer and fashioned wooden trestle legs to level and stiffen the stand.
Despite the blemishes induced by my own startling lack of patience, the surface is plenty flat enough for plane sole flattening and if you avoid the two pitted areas, it is also flat enough for sharpening chisels and plane irons to a mirror finish.
This project was a total success both in surface finish of the cast concrete and in the overall sturdiness and heavy weight of the table top. I still need to clean up the steel legs, give them a coat of paint to prevent rust and build a sandpaper storage caddy to fit underneath the table top.