I wrecked the rounded edge of a 4k water slip stone, probably from running it over an edge at too steep an angle. The result is that the stone began to crumble, coming apart like toast crumbs. Lumpy, bumpy and I needed it now. Lee Valley is 1,200 km away (or 10 days with help from Canada Post & Storage).

I clamped a 30cm mill file to the bench and made 40+ lengthwise passes, gently pressure and rolling the rounded edge to try to restore it. Lots of creamy-looking swarf.
I expect this would dress a 1K stone if needs be. While the grits are very fine, as you all know, they're soft-structured. Scrubbed out the file and warmed it to dry it quickly.
Done.
The 5/35 Pfeil hit a sand grain. 1K grit, 4k grit, slip on the inside and honed. Repaired.