This is known as a ‘curved’ or ‘round’ scraper and is mainly used for refining a bowl shape carved into wood.
Draw the centre line down a piece of cardstock, draw a rounded, quadrant shape on one half and cut to shape.
Fold down the centre line and follow the rounded edge using a knife or scissors.
Open it up to show the perfectly symmetrical curve, this can be transferred to the card scraper using a marker pen. You may need to make further adjustment to develop the rounded profile you want.
Clamp the scraper to a piece of scrap wood as a backing to stop movement and flexing, softer wood will work best, and use a hacksaw to cut the corners off. Once you have cut the majority of the way through, you should be able to remove the rest with a pair of pliers by bending the corner back and forth until it snaps off.
Use a file to shape this down to several flat faces before using a continuous stroke in an arcing motion to form the rounded edge.
Use the three different grit size on sharpening plates or abrasive paper to refine the edge. This process will create a burr that must then be removed. Remove the burr by placing each large face flat onto the finest sharpening plate and move back and forth.
The burnisher should be used as a final step to consolidate the steel on both faces by laying the scraper flat on the bench and using the burnisher over the edge back and forth. Next, put the scraper in the vise and follow the rounded edge with the burnisher. Start out square to the edge and the start to angle the burnisher incrementally with each stroke. This both consolidates the steel into itself and forms the cutting edge you need for scraper cuts.