Update: Sadly, David passed away on 22nd May 2022 after a long illness at his home in Hartland, with his wife Pat by his side. RIP David.
I have long been a staunch advocate of David Charlesworth's ruler trick, and indeed of techniques generally that employ carefully managed convexity or concavity to eliminate unnecessary work.
As an ironmonger who sells the materials that people wear out while doing unnecessary flattening and polishing that may seem odd; but in my experience there is more to be gained from helping people to get better value from their sharpening kit than there is from encouraging them to waste it (and their time).
As you can see, I use a strip of masking tape on my scary sharpening setup, David uses a thin metal ruler on his waterstones, but the technique itself is absolutely identical.
Over the years I have read through reams of critical analysis and debate of this technique, I have yet to encounter anything that even remotely dissuades me from my conviction that it is just a bloody good idea.
One word of warning though - especially if you are a student using tools at a woodworking school or college...
***** NEVER RULER TRICK A CHISEL *****
Unlike plane irons, the flat side of a chisel needs to be on the concave side of flat, so we use a different technique for them, we will cover that in a later blog post. If you do this to a chisel you will soon encounter the wrong side of your tutors and technicians.
Anyway, here it is, 'the ruler trick' in David's own words:
David is one of the world's leading authorities on fine woodworking, he offers one on one and small group training courses at his workshop in Hartland, Devon, plus a superb range of information packed educational DVD's for those unable to visit. For more details of these, please visit David's recently updated website www.davidcharlesworth.co.uk.
That's it, twelve short strokes, just the barest whiff of polish exactly where it's needed.