Much has been written about the uses of a crowned, or cambered or radiused, edge on plane irons. I’m no expert on woodworking technique so I’ll leave those details to others more qualified to discuss how to put a crowned blade to best use. And much, too, has been written about how to create a crowned edge. When hand sharpening a plane blade it is almost easier to add a bit of crown than not to, especially when the honing action is diagonal or side-to-side, as it usually is when free-handing the blade on the stones. The tendency is to apply extra pressure on the corner of the blade that’s leading the way. Back and forth like that and you’ll have worn a bit more blade off of the corners – a crown is born!
Honing guides are useful helpers at the sharpening bench. They can allow you to repeat a specific angle reliably, bear down hard to re-shape an edge (often eliminating the need for a powered grinder), work the tiniest micro-bevel to save time and effort and, yes, they can be employed to add a bit of crown to a blade. Most honing guides will allow some small amount of slop if you add pressure to one corner, then the other as you stroke the blade along the stones. By doing so, you’ll create a curved, crowned edge. Lee Valley even offers an aftermarket camber-roller that replaces the cylindrical roller in their MkII honing guide which makes it easy to tilt the guide as you hone. Rock and roll!
Enter Dave Powell of Powell Manufacturing, the man who started DMT, the diamond abrasives experts. Dave has teamed up with Toshio Odate to make a diamond honing plate that creates a crowned blade automatically (well, not really automatically – you still have to push the blade back and forth on the plate). The plate has a longitudinal semi-cylindrical hollow shape that is 2.5 thousandths of an inch (0.0025”) deep. Honing a blade in the concave channel will put a 2.5 thou crown on the blade.
The Powell Odate Crowning Plates come in four grits: 60 micron (220-grit), 45µ (325-grit), 25µ (600-grit) and 9µ (1200-grit).
After refining your new crowned edge with the 9µ plate, you use Powell’s Odate Dressing Plate, which is convex by 0.0025” to dress a hollow in one side of your 4000- and 8000-grit waterstones (Norton white and gold stones are recommended by Powell.) Now you can continue to refine and polish your crowned edge on the fine stones.