It's a funny world. When I invented carbide mandrels in the 1908's I bought a large number of custom pieces of carbide - what you're calling "bushings", thinking there would be a big learning curve. Got a good price on them for quantity, and the fact that everything was less expensive, so it wasn't even that painful. It also turns out that they are incredibly durable, and the first set I made worked perfectly. Good chance if I hadn't asked Paul Costain to make me a set for his Uni-Loc pin that cat would still be in the bag. Don't ever let it be said Paul would let a promise of secrecy keep him from marketing a good idea.
Anyway, I've got a drawer full of those damn blanks, and it's my feeling that carbide back then was better than it is today.. In almost 35 years I've only worn out one set - the pin I use most often - and I still use that set for undersizing prior to finish. So I've got this big pile of blanks that I'll probably still have when I die.
TW
