Definitive Guide to Spindle Speeders, Speed Increasers ...
For my mill, I wouldn't be using the quill, so the shaft would just clamp to the mill head directly for support. This is the first time I've seen it done on a manual mill: He's using a small 1.5mm endmill to cut a hex shaped hole in the workpiece rather than broaching. Install the high speed spindle inside the main spindle with a flexshaft