The ruler trick

[Rob Luter]

I've been learning to sharpen for several years, and thought I was pretty good at it. I recently spent a few hours in my shop escaping the summer heat, and decided to get everything all sharpened up in anticipation of the next project. While I've always flattened and lapped the backs of my plane irons, this time I decided to employ David Charlesworth's "ruler trick" to assure the back of the iron near the cutting edge was as flat and smooth as possible. The results were nothing short of amazing. I thought I was getting sharp before, but I'm getting a whole different class of results now. My planes have never cut smoother. It was a simple change that made a big difference. Maybe I'm late to the party, but better late than never.

[Robin Frierson]

What is the ruler trick?

[Phil Mueller]

Robin, it's a technique David shares on his sharpening video. Downloads and DVDs are available through Lie Nielson. You essentially wet a fine stone, and "stick" a metal ruler along one long end of the stone. Place the plane iron back side down on the ruler perpendicular to the stone and run the back of the cutting edge (a few mm of it) back and forth over the opposite edge of the stone. Creating essentially a very slight up bevel to the back of the iron close to the cutting edge.

[Rob Luter]

What is the ruler trick?

What Phil said. It takes much or the work out of flattening the iron at the cutting edge as you only are dressing the 1/4 inch or so at the edge. The amount of back bevel is all but impossible to measure. Google "The Ruler Trick" and you'll get all sorts of results, how to videos, etc.

[Robert Engel]

Its an innovation, but keep a couple things in mind.

1. I view it as a permanent alteration to the blade.
2. Difficult to do on a cambered iron.

[Mike Holbrook]

Most of my plane blades are hollow ground and cambered. I am wondering if any one who uses these methods also uses the ruler trick? It seems like the method would involve moving the blade in an arch across the stone, much like is necessary to make the camber in the first place.

[Megan Fitzpatrick]

Here's a link to David Charlesworth's article on the subject, for those interested: http://www.popularwoodworking.com/te...he_ruler_trick

[Robert Engel]

Most of my plane blades are hollow ground and cambered. I am wondering if any one who uses these methods also uses the ruler trick? It seems like the method would involve moving the blade in an arch across the stone, much like is necessary to make the camber in the first place.

I've wondered about this, too. Never tried it probably never will.

I think there's a certain amount of hype associated with this. Seems to me just a way achieve an edge quicker. I can't really see that much difference in performance and there is no perceptible difference in sharpness or blade life to me.

Can anyone tell me if there IS any advantage to a back bevel performance-wise?

[lowell holmes]

I've wondered about this, too. Never tried it probably never will.



Can anyone tell me if there IS any advantage to a back bevel performance-wise?

YES, there is! My apron plane was a disappointment until I read and did the ruler trick.

[Patrick Chase]

What Phil said. It takes much or the work out of flattening the iron at the cutting edge as you only are dressing the 1/4 inch or so at the edge. The amount of back bevel is all but impossible to measure. Google "The Ruler Trick" and you'll get all sorts of results, how to videos, etc.

You shouldn't be working anything like 1/4" with the ruler trick.

David's recommended configuration corresponds to about 1/2 degree of back-bevel, so if you work 1/4" back from the edge you'll have relieved the edge by 0.25*tan(0.5) = 2 mils. That doesn't sound like much, but it's way more than you need.

In my experience working back by 1 mm (~1/3 mil or 9 microns of relief) is enough to work through routine scratches and get a clean edge, assuming the back is reasonably well prepared to begin with.

[Patrick Chase]

Its an innovation, but keep a couple things in mind.

1. I view it as a permanent alteration to the blade.
2. Difficult to do on a cambered iron.

Neither of these is remotely true.

It's only permanent if you bungle it by working too far back from the edge (for example the "1/4 inch" suggestion). If you keep it within reason it amounts to ~10 microns of relief, and that will come out very easily in any subsequent flattening, without any significant impact on overall blade thickness. I've removed more "ruler trick bevels" than I can count.

To ruler-trick a cambered blade you simply pivot the blade over the ruler as you work. At any given position the section of the camber parallel to the ruler is the part being worked (assuming a flat back, if the back is "twisted" then there will be a rotational offset). I was able to do it on my first try once I'd worked out the physical principle.

For some reason the "ruler trick" is utterly mired in disinformation and bad advice. It blows my mind that something so simple could become so confused.

[Jim Koepke]

... It blows my mind that something so simple could become so confused.

Alas, as a member of the flat bevel society, it is very clear that keeping things simple is always subject to confusion and ridicule.

jtk

[Jim Koepke]

You shouldn't be working anything like 1/4" with the ruler trick.

(edit)

The way I understand the ruler trick it would be very difficult to produce it over a 1/4" depth.

jtk

[Patrick Chase]

The way I understand the ruler trick it would be very difficult to produce it over a 1/4" depth.

jtk

As I said above that corresponds to a couple mils of relief at the tip, so not that difficult if you use a medium stone (which you are absolutely not supposed to do).

[Robin Frierson]

I have been down the road of the back bevel and prefer not to use it. Each time I did the back bevel it got wider and wider. So I would increase the bevel and before long I had a 5 deg back bevel, combined with my 5 deg front secondary bevel, I was at 35 degrees. Which is ok for some woods. I probably made my back bevel too wide..but how do you only fit 10 micron of blade on the stone and maintain that. Perhaps if I had seen the video I may have had better results. I still have blades I need to regrind to get rid of those back bevels.

Once I do the work of mirroring the back then it just takes a minute to remove the wire edge and polish the back edge each time. I no longer use stones for the back, prefering 24inches of micron graded sandpaper on a granite plate. But whatever works...we all have different techniques for getting it done.