Had a classic OOOOPs moment.
I was making split-brasses for my steam-wagon's two big-ends, the first time I've attempted making bearings in that way, and after some experimenting with the first pair had produced three bushes, still soldered together, and was chamfering the rims of their bores. I'd set out to make spares, and the first pair are serviceable enough for that.
By now of course, everything – lathe, tools, me – was clarted in gun-metal granules but I carried on and when I found the bronze a bit unexpectedly resistant I assumed the usual – worn boring-tool insert, wrong insert for the metal anyway, slightly off-height, perhaps wrong angle of attack.
Anyway this operation was not critical and using the edge of an HSS lathe tool as a scraper on the bush removed from the lathe removed the raised burr. I'd also turned a mild-steel plug-gauge and found this quite an effective finishing burnisher, rotated by hand.
Happy with the finished bushes, I started to brush the lathe down, and what should appear from under the swarf on the bed?
Only the tiny boring-bar insert!
Goodness knows when it had fallen out, but the heap of swarf on the boring bar hid the fact that I'd been chamfering the bushes with the edge of the holder itself….
…. Ooops.