I use 0.8mm drills all the time to drill through titanium.
I find the best method to sharpen small drill bits is not using
ie. sanding or other disks. There is always a possibility of
overheating the tip. Also it is easier to control and see what you are
doing. I use a medium ‘easylap’ diamond file.
1st, it is important to remove any nasty ends from broken drill bits
or any blued, or overheated areas before starting the sharpening
process. 2nd, position a strong light at such an angle so that the
light reflected from the faceted tip will shine into your eye when you
place the blunt tip against your bench pin. Wear magnification lenses.
Indeed take a new sharp drill and hold it against your bench pin and
observe the shape of the facets of the sharp drill. Try to copy the
angles, or establish the angles you require for the metal you are
using, with the reflected light shining of the facets.
Test the sharpened drill before doing something important. Use lots
A pin vice is helpful.