Machine grinding is a far more aggressive process than abrasive paper. You don't get sparks flying off your bushes when you are sanding, at least I don't
Case Hardening is far harder than titanium or stainless, so you would still have the problem, it's a case (pardon the pun) of damage limitation. The only way around that is diamond or boron. Diamond bushes, that will get more women interested in turning!
The harder the material the harder it is to produce bushes from, this makes it more expensive (coupled with the greater expense of the raw material). Case hardening uses mild steel (which is easy to machine) and then it is case hardened which forms an incredibly hard skin on the item. That's is why lock shackles etc, are case hardened, have you tried cutting through one of those? Doable, but not easy.
You need to investigate hardness figures (Rockwell, Brunell, Vickers etc.) for the various materials and make an informed decision based on that harder the finished bush, the longer it will last.
Dan, the best process (IMHO)for making bushes would be: -
Using Bright Mild Steel
Face off bar
Drill hole
Ream hole
Turn outside diameters.
Part off
Grind outside diameters
Case harden
Result, precision, longer lasting bush.
More expensive, but they will last a long time.
That is how we would have done it in the aircraft industry toolmaking department where I worked for a number of years.
