Here's an idea I had for a tool to aid in nail-making. It incorporates ideas I've 'borrowed' from a number of sources.
Basically it's a piece of 50x50x6mm (2x2x1/4 inch) mild angle with angled slots filed into it. The bottom of each slot acts as a cutting edge and the top of the edge is recessed 1mm from the top of the tool. This prevents the nail being cut completely though, saving the nail, the tool's edge and the hammer's face. It also allows the tool to be left in the hardy-hole constantly, much safer than doing so with the hardy-cutter. At the opposite end a piece of 3mm (1.8 inch) mild is welded on, with a tapped hole in line with each cutting recess. In use a machine screw is inserted into each hole with a hex-nut jam-locking it into place, making for a simple but adjustable stop for faster, more accurate cutting. I have shown the tool with a piece of angle-iron welded on as a hard-shank but any suitable way of securing it would work.
I invite and welcome your comments and suggestions!