A sharp concave card scraper will reproduce the negative profile to itself easily and crisply, making the clean up and smoothing of spindles, beads, etc. much easier.
Here's how I sharpen mine
Step 1: Watch the Short Video First
Watch the video, then read through the more detailed steps. This should help you understand the process more easily.
Step 2: Make a Sharpening Profile
Use the concave card scraper to produce a short length of profile.
Make the profile slightly smaller than the curve of the scraper. You'll see why later.
Clearly, this is best done when it is sharp, so try to remember this when you buy new profiled scrapers. Angle the scraper to make the profile slightly smaller.
If the scraper is already dull, then you may find it difficult, and using a rasp and flat file may speed the process up.
Step 3: For Damaged or Badly Dulled Scrapers, File First
If your concave card scraper is nicked or very dull, then use a half-round or round file to prepare the edge. You want the 'thickness' of the scraper to be at ninety degrees to the faces, so keep the file at ninety degrees too.
Step 4: Smooth the Edge
Wrap some fine sandpaper over the profile you previously prepared, and use this to smooth the edge of the scraper curve. The thickness of the sandpaper is why we make the profile slightly smaller.
Remember to keep the profile and scraper face at ninety degrees to one another.
Step 5: Create the Sharp Corner That Does the Work
Now place the scraper face down on a fine india stone (or fine water stone, etc.) and rub off any burrs and unevenness at the cutting edge.
Step 6: For the Best Finish
Repeat on a flat piece of MDF, charged with honing compound, for a superior finish.
Step 7: Polish the Concave Edge Profile
Finish by polishing the edge, using the prepared profile, now charged with honing compound.
You can repeat these final two steps frequently as you use the scraper, to keep a keen edge and save having to go back to step 1.
Step 8: Now You're Ready to Scrape!
I hope you've found this instructable useful.