I started free hand grinding my own drill bits a few months ago. Not
out of choice, but out of necessity. Since I started doing it I have
reground a fair number of them. Sometimes the same one two or three
times in the same set of jobs. Now I have old eyes, but my glasses are
pretty good, and I have a magnifier lamp I swing over my bench grinder.
It allows me to free hand better than I ever thought I would be able to.

I've also resharpened some of my stub length Silver and Deming bits.
That's where it really pays off. I bought a set of those some years
back, but I've never seen them available singly. The 5/8 took quite a
beating over the years since its the standard injection port size for
hand injecting plastisol. I actually make injectors .620 and sprues
..63, but sometimes you just have to brute force a solution. It was nice
to finally be able to just sharpen it right up.

No more piles of drill bits to be sharpened someday. I just sharpen it
right up and drop it back in its spot. Which brings me to the other
size limit.

The smallest I've reground so far was a #21. I picked that one to push
the smaller size limit because I have several of them on hand. I
ordered a half dozen of them once from McMaster in stub screw machine
length to drill molds for 10-32 clamping screws. It came out ok. I'm
not sure how much smaller I could grind free hand. Probably not much.
I was squinting a bit at it and gritting my teeth. LOL. So how small
of drill bits do you free hand regrind. I don't have a drill doctor or
a Darex or a knockoff. Just a bench grinder. Well a couple of them and
a small belt grinder now.

I think one of the limits is grit size, but another would be heat. It
would be really easy to overheat a tiny little drill bit.