Thank you for sharing Frank.

I think what is more impressive is the fact someone has been able to make a drill that size. It must be fluted to allow the swarf to escape so the outside diameter is 0.004" but the core will be even smaller let alone grinding the cutting clearance angle on the tip. This to me is a fantastic achievement in making the drill let alone using it. I calculated the spindle speed would be 76500rpm for mild steel. I use 0.2 mm cutters at work on a CNC engraver but only on plastic and depth of cut 0.02 mm per pass. So appreciate the difficulty in using this sized diameter drill

Formula used to calculate spindle speed:
Cutting speed of mild steel 24 m/min x 1000 / Pi (3.14) x diameter of drill (0.1 mm). Therefore 24000/0.314=76433 rpm

The spindle speed also leads to another engineering problem.

The Home Engineer