I used to sharpen my card scraper with a screwdriver. But I was not satisfied with results. A good manufactured burnisher costs in my place about $40. Thats too much for me. But what is a burnisher? It is a rod of polished hard steel and some handle. No more. It reminded me a HSS drill bit shaft. So I made my DIY burnisher from 8 mm HSS drill bit, gluing it to self made handle from beech with epoxy glue.
Sharpening my card scraper on a water stone:
Here I use wooden block to keep card scraper vertical while sharpening:
Trimming the flat side of the card scraper with the burnisher:
Trimming the edge of the card scraper:
Test on a pine board:
I am pretty sutisfied with the result. That was my best try on card scraper sharpening.