I'm planning a round column-based QCTP similiar to this http://www.gadgetbuilder.com/ToolHolders.html#Round_QCTP ....for my Sherline CNC lathe. My main reasons for the round column format (vs. square dovetails-based versions) is the ease of tool holder creation.In designing it to keep the cutting tools within the same space the Sherline standard tools inhabit, while require the column to be approximately 3/4" diameter, with a flat 1/8" square base for mounting to the T-slots. As this is a bit narrower than the standard 1.25" diameter square column Sherline tool holder, I am a bit concerned about rigidity. My original plan was to go with aluminum, but knowing the column diameter will be thin in encouraging me to go with steel. I use this lathe for steel and stainless, so I think the aluminum would be tool weak. I'm looking for suggestions as to what steel I should select for the tool post (and tool holders). I've considered stainless (merely because of the corrosion resistance) but I'd rather lean on the side of strength. I have no surface grinding capabilities but was also considering steel that can be hardened (via propane/acetylene). I also haven't ruled out that I'm over-engineering this and that simple unhardened steel would be enough. Any thoughts on the choice of metal?