	Abrasives
	Finest abrasives.
	Microbevels front and back.
	Use a jig.

	Copyright (c) 2002-15, Brent Beach

The Ruler Trick

Introduction - what is the trick?
The geometry of wear bevels - bevel down and bevel up.
What the ruler trick must accomplish.
Conclusions

Introduction - what is the trick?

This picture comes from Hand Tool essentials from Popular Woodworking, page 48, in an article by David Charlesworth titled The Ruler Trick. The text does not say, but I have assumed that the stone is 2" by 8" and the ruler width is around 0.32" (8 mm). The line on the right is actually 0.4" (10 mm) from the edge, not the 5/8" mentioned in the text. Since Charlesworth works in metric, I assume this is a conversion error.

This is a sketchup model of the plane iron, ruler and stone.

The model allows us to get a closeup of the geometry of the honed bevel we get when we use this trick. Using the ruler thickness of 0.5mm (0.02") we find that the honed bevel varies between 1.08 degrees when the blade is 5/8" in from the edge and 0.68 degrees when the blade edge is at the stone edge.

The geometry of wear bevels - bevel down and bevel up.

This is a sketchup image of a worn plane iron. The drawing shows the iron in about the position is has in use.

The wear on the lower face is short and curves steeply to the worn edge. The wear bevel on the upper surface is longer and curves more slowly to the worn edge.

The drawing applies whether the plane iron is bevel up or bevel down. Same drawing but a crucial difference! With a bevel up iron, the short steep wear bevel is on the back face not the bevel face. With a bevel down iron, the short steep wear bevel is on the bevel face (the front face in my usage).

What the ruler trick must accomplish.

The ruler trick, given the geometry in the description in Hand Tool essentials, creates certain angled honed bevels on the back face of the blade. In this drawing I have used the largest angle for the whole honed bevel. In fact, the honed bevel would be an arc with a continuous curve between this largest angle and the smallest angle.

What effect does this variation in honing angle have on honing time? When the blade edge just comes onto the stone, the honed angle is 0.68 degrees. As the blade moves in, the angle increases with honing at the edge at a final angle of 1.08 degrees. As the blade edge moves back toward the stone edge, the blade edge actually lifts off the stone and the blade is sliding on the honed bevel back of the blade edge. Most of the time, honing is occurring back of the blade edge.

Plane iron, two possible ruler trick honed bevels This sketchup model shows two possible results of using the ruler trick. The orange bevel is at 1.08 degrees to the back face and is

Conclusions

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