(Thanks, Dennis, for helping me get this posted.)
I wanted to post this sketch as a followup to a post on the "straight touch hole" string. This is a sketch of the touch hole coning tool described in the Journal of Historical Arms Making Technology. The article is a translation of an old german booklet describing gunsmithing tools using in the 18th c. In a somewhat ambiguous manner, the article describes the tool as being used by clamping the tang of the tool in the vise. I discussed this tool with Richard Sullivan (during a visit to Colonial Williamsburg in 2009). If I remember correctly, his comments agreed with the article--that the tang of the tool was clamped in the vise, then the breach of the barrel was slipped up over the tool, such that the conical cutter fitted into the bore-side of a straight-drilled touch hole. The smith then pressed the barrel against the cutter as the knob was cranked. This yielded a touch hole drilled straight on the outside, but coned on the inside. I hope my sketch makes it clear how the cutter works. By having four gears, a clock-wise turn of the handle serves to turn the cone-shaped cutter clock-wise.